Rare earth doped zinc oxide nanophosphor powder: a future material

Rare earth doped zinc oxide nanophosphor powder: a future material for solid state lighting and solar cells. Vinod Kumar, OM Ntwaeaborwa, T Soga, Vire...
1 downloads 0 Views 5MB Size
Download PDF
Review Cite This: ACS Photonics 2017, 4, 2613-2637

pubs.acs.org/journal/apchd5

Rare Earth Doped Zinc Oxide Nanophosphor Powder: A Future Material for Solid State Lighting and Solar Cells Vinod Kumar,*,† O. M. Ntwaeaborwa,‡ T. Soga,§ Viresh Dutta,† and H. C. Swart∥ †

Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi 110016, India School of Physics, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa § Department of Frontier Materials, Nagoya Institute of Technology, Nagoya 466-8555, Japan ∥ Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa

ACS Photonics 2017.4:2613-2637. Downloaded from pubs.acs.org by UNIV AUTONOMA DE COAHUILA on 04/26/19. For personal use only.

‡

ABSTRACT: A comprehensive review of up-conversion (UP) and down-conversion (DC) or down shifting of rare earth (RE) doped zinc oxide (ZnO) nanophosphors is presented. Research interest in the development of RE3+ doped ZnO for UP and DC nanophosphors has been encouraged by the potential application of these materials in light emitting diodes and different types of photovoltaic cells. A range of remarkable characteristics, which are organized into different sections describing the structure, optical, and luminescence properties of these materials, are discussed in detail. Undoped ZnO has two characteristic emissions in the ultraviolet and visible regions related, respectively, to excitonic recombination and intrinsic defects. X-ray photoelectron spectroscopy (XPS) data demonstrated a correlation between the visible emission and intrinsic defects. In the case of the DC or shifting process, there was simultaneous emissions related to f → f transitions of RE ions and defects in ZnO host. These emissions were dependent on the synthesis method, annealing temperature, and RE ion concentration, among other things; only f → f transitions of RE ions were observed in the case of the UC process. These down and up conversion RE doped ZnO phosphors were evaluated for a possible application in solid state lighting and photovoltaic cells. KEYWORDS: ZnO, Rare earth, Solid state lighting, Solar cell, Up conversion, Down shifting band gap of ZnO to ∼3.63 eV (342 nm).10 Soosen et al.11 observed red-shifting of the maximum wavelength of the absorbance peak, and they attributed it to the decreasing quantum confinement effect due to increasing crystallite size. They were able to shift the absorbance edge from 362 to 381 nm by annealing 5 nm ZnO particles at different temperatures and effectively increasing the particle size up to 8 nm. Their UV absorption results also showed that quantum confinement resulted in an increase in the energy value of the optical band gap. A chemical reaction can lead to a substitutional replacement of the lattice atoms with doping ions into the crystal structure of the compound. Kamarulzaman et al.12 have shown that band gap widening occurs in all undoped and doped ZnO nanostructures, compared to the band gap of bulk materials. However, doping ZnO nanostructured materials with transition metals such as Cu and Mn caused the band gap to become narrower. The size of the crystallites (micro- or nanosized) and the type and concentration of the doping involved play the most important roles in the band gap narrowing and widening process. The widening in the band gap

In the past few decades, research interest in zinc oxide (ZnO) semiconductor materials has grown exponentially as observed from a growing number of publications in these materials. ZnO is nontoxic, and it can be produced cost effectively on a small or large scale. It has three types of unit cell structures, namely, hexagonal wurtzite, zinc blende, and rock salt as shown in Figure 1.1 The hexagonal wurtzite phase is the most popular structure due to its stability at room temperature and normal atmospheric pressure. The atomic arrangement of the wurtzite structure is comprised of four zinc ions (Zn2+) occupying the corner of a tetrahedral coordinate with one oxygen ion (O2−) located at the center and vice versa. The growth of zinc blende structure of ZnO is challenging because the zinc blende ZnO is only stable in the cubic structure. In the rock salt structure, each Zn or O atom is surrounded by its alternative six nearest neighbors. It only exists at the higher pressures (15%) silicon solar cells conclusively showed an enhancement in shortwavelength spectral response. It was mainly due to the DS effects of the phosphor NPs.207 Wu et al. explored the development of a ZnO:Eu3+ bifunctional layer for use in the inorganic solar cells.210 The bifunctional layer is used as a spectral conversion layer as well as an electron transport layer. To detect the influence of Eu3+ doping on photoactive performance, ZnO:Eu3+ was used as an electron buffer layer in layered organic solar cells with layer configuration ITO/ZnO:Eu 3+ /P3HT:PC61BM/MoO 3 /Al, shown in Figure 26a. The J−V curves of the devices are shown in Figure 26b. A slight increase is observed in the short circuit current density (JSC) from 8.94 to 9.11 mA/cm2 when using ZnO and ZnO:Eu3+ as a buffer layers. This is attributed to a spectral DC process.202 Yao et al. used RE doped ZnO UC/DC materials to enhance the PCE of DSSCs.211 The J−V curve of the DSSCs based on UC/DC phosphors are shown in Figure 27. The optimal efficiency was ∼5.13% with the incorporation of UC and DC materials, which is higher than that of DSSCs based on TiO2. This enhancement is attributed to increase of light harvesting via converting UV and NIR into visible emission using DS and UC luminescence processes, respectively.

■

APPLICATION OF RARE EARTH DOPED ZnO Solar Cells. There is an existing mismatch between the conventional single-junction solar cell spectral response (SR) and the solar emission spectrum. It is due to the limited efficiency absorption of the semiconducting material using for the active layer of the solar cell. So, this is the origin of the major amount of losses in commercially available solar cells. The efficiency of the solar cell has a limitation due to these spectral losses. The theoretical maximum efficiency of a singlejunction solar cell consisting of a semiconducting material having a bandgap of ∼1.1 eV (Si) is ∼31%. This is called the Shockley−Queisser limit of the device.201 A large part of sunlight is absorbed in the approximately first micrometer of a semiconducting material. Much research has been done to optimize the top surface of solar cells. The probable increase in the solar cell’s SR passes through making better use of the short-wavelength photon. There are three kinds of losses in a solar cell, which can be reduced by the modification in the spectrum. The first two are thermalization and transmission. Thermalization losses are prominent in smaller band gap material based solar cells, while transmission losses are common in the wider band gap material based solar cells. An electron−hole pair with higher energy is created when a semiconductor absorbs a photon of higher energy than the band gap, and the excess energy is dissipated in the form of heat. The third loss mechanism is insufficient collection of photon-generated carriers due to recombination close to or at the surface. Since photons of high energy are absorbed in this region, the result is a reduced SR at shorter wavelengths. This loss can be reduced using the process of photon conversion, whereby photons are shifted into an energy range where the cell has shown a higher SR. The photon flux as a function of wavelength is shown in Figure 25. The wavelength conversions

Figure 25. Photon flux as a function of wavelength (AM 1.5G Solar Spectrum). Reproduced from ref 202 with permission. Copyright 2012 Royal Society of Chemistry.

of photons are a promising route to decrease the spectral mismatch losses. Therefore, it is considered to be the major part of the efficiency losses in PV devices. Wavelength dependent spectral converters have been explored for enhancing the energy conversion in single junction solar cells in recent years. There are three luminescence processes (QC, DC, and UC). These three approach have potential to enhance the efficiency of solar cells. QC through 2629

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

Figure 26. (a) The schematic structure of ZnO:Eu3+ based inverted organic solar cells. (b) J−V curves of the inverted organic solar cells using ZnO and ZnO:Eu3+ as a buffer layer. Reproduced from ref 210 with permission. Copyright 2015 IOP Publishing.

persistence, and possible energy savings.206−208 Normally, three different approaches can be used for generating white light emission based LEDs. The first approach is by the mixing of three LEDs, namely, red, green, and blue (RGB), together, the second one is by using an UV LED to stimulate RGB phosphors, and the third one is by using a blue-emitting diode that excites a yellow-emitting phosphor. Today’s commercial phosphor converted light emitting diodes (pc-WLEDs) normally use a 450−470 nm blue GaN LED chip covered by a yellowish YAG:Ce phosphor coating. However, these pcWLEDs have some weaknesses, such as a poor color rendering index and low stability of the color temperature,217,218 since white light emission is generated by the combination of the blue light emitted by an LED chip and the yellow light emitted by the YAG:Ce phosphors. The RGB LEDs require different driving currents for different color LEDs, complicating their fabrication.219 White UVLEDs are fabricated by using UV-LED chips that are coated with white light-emitting single-phased phosphors or RGB tricolor phosphors.218−220 A great challenge is to produce a single phosphor that can be used to achieve white light emission. Ji et al. have developed a novel two-step method for the synthesis of isocrystalline core−shell nanocrystals of ZnO:[email protected] An efficient energy transfer was observed from ZnO to Tb3+ ions. RE doped isocrystalline core−shell (ICS) nanocrystals have excellent optical properties with possible applications to be used as light emitting devices. RE ions (Tb3+, Dy3+, and Er3+) are incorporated into ZnO nanostructures using ICS. These core−shell spherical nanocrystals lead to an increase of the ZnO band-edge absorption in PLE and to the improvement of the characteristic emissions of the RE ions compared with the core-only. So inner doping and efficient energy transfer from the ZnO host to the doped RE ions are realized. These RE doped core−shell nanocrystals are ideal candidates for light emitting device applications.222 The CIE diagram of undoped and RE doped ZnO NPrs under different conditions is shown in Figure 28. According to our previous reported work, ZnO has broad emission range from red to white light to green to blue. So we can control the emission light with the variation of defects, different dopant ions, and doping concentration. The question may arise: What is the real quantum efficiency of ZnO and RE doped ZnO to be used in SSL and solar cells? The overall efficiency of white light LEDs is clearly dependent on the development of highly efficient, environmentally friendly, and inexpensive phosphor materials. Balestrieri et

Figure 27. J−V curve of UC/DC based DSSC. Reproduced from ref 211 with permission. Copyright 2015 Elsevier.

The PV systems should maintain the initial efficiency over a lifetime of at least 20 years. It must be not only mechanically stable but also resistant to degradation caused by exposure into the environment. To succeed in the implementation of UC/ DC optimized solar cells in commercial systems more work must be directed to improving their stability and robustness in ambient conditions. A significant efficiency enhancement in UC/DS based solar cells is still a major challenge.212,213 Solid State Lighting. The high energy demand adding increasing pressure on fossil fuel reserves increases on a daily basis. The impact on the environment is tremendous.214 Conventional incandescent and fluorescent lamps rely heavily on either heat or the discharge of gases. These phenomena are associated with a huge amount of energy losses due to the high temperatures and involvement of large Stokes shifts.215 A new kind of lighting device was invented by Nichia Chemical Company using a blue InGaN LED chip coated with yttrium aluminum garnet yellow phosphor (Y3Al5O12:Ce, YAG:Ce) in 1996.216 The InGaN chip emits blue light through an electron− hole recombination in the p−n junctions. Some of the blue light from the LED excites the YAG:Ce phosphor, consequently emitting yellow light and then the rest of the blue light from the InGaN chip is mixed with the yellow light to generate white light. This light emission process by an LED is called solid-state lighting (SSL). The main advantages of SSL are small size, high luminous efficiency, ecofriendly nature, long 2630

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

used to achieve NIR EL. The aforementioned multicolor and NIR EL originating from the impact excitation of the RE ions incorporated into the ZnO host can be activated with threshold voltages as low as ∼5 V. Another possible obstacle in the use of phosphor materials that has to be overcome is the degradation of phosphor materials with time in different environments and conditions.231

■

CONCLUSION ZnO is a low-cost, ecofriendly, and versatile material to be used to generate emission colors all over the rainbow spectrum. The reason for the color tuning is the band edge emission as well as the different defect related emissions. The defect related emission in ZnO is dependent on the synthesis method, annealing temperature, and several other parameters. The O 1s XPS peak was correlated to the defect related emission in ZnO. The emitted color can easily be tuned by doping with the appropriate RE materials. RE doped ZnO nanophosphors can be synthesized by different methods. The emitted light can be tuned throughout the visible range by using different RE dopant materials or different synthesis techniques. ZnO can also be used as the host of dopant ions for up and down conversion. The up and down conversion nanophosphor materials can be used to enhance the efficiency of solar cells. This enhancement in the efficiency is due to the enhancement of light harvesting via converting UV or NIR to visible emission. To succeed in the implementation of up and down conversion ZnO optimized solar cells in commercial systems, more work must be directed to improvement of their stability and robustness in ambient conditions because the solar cells should maintain their initial efficiency over a lifetime of at least 20 years and they must be, therefore, not only mechanically stable but also resistant to degradation caused by exposure to the environment. For the SSL point of view, a stable and high color purity single host based white light emission is under development. This review concludes that RE doped ZnO nanophosphors will be promising up and down conversion materials for future applications in solid state lighting and solar cells.

Figure 28. CIE diagram of undoped and RE doped ZnO NPrs with different synthesis condition.

al.223 showed that although the DC theoretical value of splitting one photon into two photons is 200%, the experimentally obtained results for example Pr doped ZnO and codoped Pr and Yb ZnO thin films is still very low. Sun et al.224 prepared Ln doped ZnO quantum dots (QDs) by a sol−gel method. The doped QDs exhibited enhancement of the luminescent properties and quantum yield. For lightly S doped ZnO powder an efficiency of 55% was observed, while at higher doping concentrations, the efficiency was higher (75%), and further improvement may be possible by optimization of the excitation wavelength.225 Elleuch et al.226 used ZnO;Er thin films for DC photon generation and a possible application as antireflective layer, when placed in front of Si solar cells. A low reflectance and high refractive index of the film were measured at 632 nm. DC was also achieved for this film under visible excitation by 980 nm photons, which might be useful for Si solar cell. In the light of current available literature, it is clear that excellent measured values of efficiency are difficult to find, and the next step therefore will be to obtain the real efficiency and to test these materials in real industrial environments. A limited number of research reports on electroluminescent (EL) thin films for LED applications utilizing RE doped ZnO have been published.227 Most of the investigations on LEDs are based on ZnO:Er films, for achieving green and NIR (∼1.54 μm) EL.227 The visible and ∼1.54 μm EL from an n-ZnO:Er/pSi heterostructure under reverse bias with a threshold voltage of ∼10 V was reported by Harako et al.228 LEDs fabricated using these samples exhibited bright green (536 and 556 nm), red (665 nm), and 1.54 μm emissions. Francesco Pecora et al.229 demonstrated an LED device based on a Si-rich ZnO:Er/p+-Si heterostructure, which exhibited detectable ∼1.54 μm emission under forward bias with a threshold voltage of ∼15 V. By incorporating Si atoms, it was demonstrated that the Si mediated enhancement of PL intensity on the Er-doped ZnO and EL. A low-voltage driven ZnO:Er/p+-Si heterostructured device (∼1.54 μm EL) was developed by Yang et al.230 A novel device structure was developed using ZnO:RE as a lightemitting layer, capped by MgxZn1−xO layer. They have successfully obtained red, green, and blue EL from the devices using ZnO:Eu, ZnO:Er, and ZnO:Tm films as the lightemitting layers, respectively. ZnO:Nd and ZnO:Er films are

■

AUTHOR INFORMATION

Corresponding Author

*E-mail addresses: [email protected], [email protected] (Vinod Kumar). ORCID

Vinod Kumar: 0000-0002-6425-5120 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS One of the authors (V.K.) is thankful to DST, New Delhi, India, for support through DST-Inspire faculty award [DST/ INSPIRE/04/2015/001497].

■

REFERENCES

(1) Coleman, V. A.; Jagadish, C. Zinc Oxide Bulk, Thin films and Nanostructures Processing, Properties and Applications, 1st ed.; Elsevier Science, 2006. (2) Park, Y. S.; Litton, C. W.; Collins, T. C.; Reynolds, D. C. Exciton Spectrum of ZnO. Phys. Rev. 1966, 143, 512−519. (3) Rusdi, R.; Rahman, A. A.; Mohamed, N. S.; Kamarudin, N.; Kamarulzaman, N. Preparation and Band Gap Energies of ZnO

2631

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

Nanotubes, Nanorods and Spherical Nanostructures. Powder Technol. 2011, 210, 18−22. (4) Caglar, M.; Caglar, Y.; Aksoy, S.; Ilican, S. Temperature Dependence of Optical Band Gap and Electrical Conductivity of Sol-gel Derived Undoped and Li Doped ZnO Films. Appl. Surf. Sci. 2010, 256, 4966−4971. (5) Shan, F. K.; Liu, G. X.; Lee, W. J.; Shin, B. C. Stokes Shift, Blue Shift and Red Shift of ZnO Based Thin Films Deposited by Pulsed Laser Deposition. J. Cryst. Growth 2006, 291, 328−333. (6) Shan, F.K.; Yu, Y. S. Band Gap Energy of Pure and Al Doped ZnO Thin Films. J. Eur. Ceram. Soc. 2004, 24, 1869−1872. (7) Saleh, R.; Prakoso, S. P.; Fishli, A. The Influence of Fe Doping on the Structural, Magnetic and Optical Properties of Nanocrystalline ZnO Particles. J. Magn. Magn. Mater. 2012, 324, 665−670. (8) Chen, Y.; Xu, X. L.; Zhang, G. H.; Xue, H.; Ma, S. Y. Blue Shift of Optical Band Gap in Er-doped ZnO Thin Films Deposited by Direct Current Reactive Magnetron Sputtering Technique. Phys. E 2010, 42, 1713−1716. (9) Liu, H.; Yang, J.; Hua, Z.; Zhang, Y.; Yang, L.; Xiao, L.; Xie, Z. The structure and magnetic properties of Cu doped ZnO prepared by sol-gel method. Appl. Surf. Sci. 2010, 256, 4162−4165. (10) Debanath, M. K.; Karmakar, S. Study of Blueshift of Optical Band Gap in Zinc Oxide Nanoparticles Prepared by Low Temperature Wet Chemical Method. Mater. Lett. 2013, 111, 116−119. (11) Soosen, S. M.; Bose, L.; George, K. C. Optical Properties of ZnO Nanoparticles. SB Academic Review 2009, 16, 57−65. (12) Kamarulzaman, N.; Kasim, M. F.; Rusdi, R. Band Gap Narrowing and Widening of ZnO Nanostructures and Doped Materials. Nanoscale Res. Lett. 2015, 10, 346. (13) Gedamu, D.; Paulowicz, I.; Kaps, S.; Lupan, O.; Wille, S.; Haidarschin, G.; Mishra, Y. K.; Adelung, R. Rapid Fabrication Technique for Interpenetrated ZnO Nanotetrapod Networks for Fast UV Sensors. Adv. Mater. 2014, 26, 1541−1550. (14) Naik, K. K.; Khare, R.; Chakravarty, D.; More, M. A.; Thapa, R.; Late, D. J.; Rout, C. S. Field Emission Properties of ZnO Nanosheet Arrays. Appl. Phys. Lett. 2014, 105, 233101. (15) Kumar, V.; Singh, N.; Kumar, V.; Purohit, L. P.; Kapoor, A.; Ntwaeaborwa, O. M.; Swart, H. C. Doped Zinc Oxide Window Layers for Dye Sensitized Solar Cells. J. Appl. Phys. 2013, 114, 134506. (16) Huang, J.; Yin, Z.; Zheng, Q. Applications of ZnO in Organic and Hybrid Solar Cells. Energy Environ. Sci. 2011, 4, 3861. (17) Kumar, V.; Singh, R. G.; Singh, F.; Purohit, L. P. Highly Transparent and Conducting Boron Doped Zinc Oxide Films for Window of Dye Sensitized Solar Cell Applications. J. Alloys Compd. 2012, 544, 120−124. (18) Mishra, Y. K.; Modi, G.; Cretu, V.; Postica, V.; Lupan, O.; Reimer, T.; Paulowicz, I.; Hrkac, V.; Benecke, W.; Kienle, L.; Adelung, R. Direct Growth of Freestanding ZnO Tetrapod Networks for Multifunctional Applications in Photocatalysis, UV Photodetection and Gas Sensing. ACS Appl. Mater. Interfaces 2015, 7, 14303−14316. (19) Guo, D. Y.; Shan, C. X.; Qu, S. N.; Shen, D. Z. Highly Sensitive Ultraviolet Photodetectors Fabricated from ZnO Quantum Dots/ Carbon Nanodots Hybrid Films. Sci. Rep. 2015, 4, 7469. (20) Tian, S.; Yang, F.; Zeng, D.; Xie, C. Solution Processed Gas Sensors Based on ZnO Nanorods Array with an Exposed (0001) Facet for Enhanced Gas Sensing Properties. J. Phys. Chem. C 2012, 116, 10586−10591. (21) Zheng, Z. Q.; Yao, J. D.; Wang, B.; Yang, G. W. Light Controlling, Flexible and Transparent Ethanol Gas Sensor Based on ZnO Nanoparticles for Wearable Devices. Sci. Rep. 2015, 5, 11070. (22) Singh, T.; Pandya, D. K.; Singh, R. Surface Plasmon Enhanced Bandgap Emission of Electrochemically Grown ZnO Nanorods using Au Nanoparticles. Thin Solid Films 2012, 520, 4646−4649. (23) Wang, D.; Yang, J. H.; Xing, G.; Yang, L.; Lang, J.; Gao, M.; Yao, B.; Wu, T. Abnormal Blue Shift of UV Emission in Single Crystalline ZnO Nanowires. J. Lumin. 2009, 129, 996−999. (24) Djurisic, A. B.; Leung, Y. H.; Tam, K. H.; Hsu, Y. F.; Ding, L.; Ge, W. K.; Zhong, Y. C.; Wong, K. S.; Chan, W. K.; Tam, H. L.;

Cheah, K. W.; Kwok, W. M.; Phillips, D. L. Defect Emissions in ZnO Nanostructures. Nanotechnology 2007, 18, 095702. (25) Ozgur, U.; Alivov, Y. I.; Liu, C.; Teke, A.; Reshchikov, M. A.; Dogan, S.; Avrutin, V.; Cho, S. J.; Morkoc, H. A Comprehensive Review of ZnO Materials and Devices. J. Appl. Phys. 2005, 98, 041301. (26) Zhang, X. M.; Lu, M. Y.; Zhang, Y.; Chen, L. J.; Wang, Z. L. Fabrication of a High Brightness Blue Light Emitting Diode using a ZnO Nanowire Array Grown on p- GaN Thin Film. Adv. Mater. 2009, 21, 2767−2770. (27) Singh, T.; Pandya, D. K.; Singh, R. Concentration Dependent Structural and Optical Properties of Electrochemically Grown ZnO Thin Films and Nanostructures. Appl. Surf. Sci. 2013, 270, 578−583. (28) Janotti, A.; Van de Walle, C. G. Fundamentals of Zinc Oxide as a Semiconductor. Rep. Prog. Phys. 2009, 72, 126501. (29) Janotti, A.; Van de Walle, C. G. Native Point Defects in ZnO. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 165202. (30) Serra, O. A.; Lima, J. F.; de Sousa Filho, P. C. The Light and the Rare Earths. Rev. Virtual Quim. 2015, 27, 242. (31) de Sousa Filho, P. C.; Serra, O. A. Rare Lands in Brazil: Historical, Production and Perspectives. Quim. Nova 2014, 37, 753. (32) Steckl, J.; Park, J. H.; Zavada, J. M. Prospects for Rare Earth Doped GaN Lasers on Si. Mater. Today 2007, 10, 20−27. (33) Wang, Y.; Zhu, G.; Xin, S.; Wang, Q.; Li, Y.; Wu, Q.; Wang, C.; Wang, X.; Ding, X.; Geng, W. Recent Development in Rare Earth Doped Phosphors for White Light Emitting Diodes. J. Rare Earths 2015, 33 (1), 1−12. (34) Kobelev, N. P.; Kolyvanov, E. L.; Khonik, V. A. An Acoustic Study of Irreversible Structural Relaxation in Bulk Metallic Glass. Solid State Phenom. 2006, 115, 113−120. (35) Tyrrell, G. C. Phosphors and Scintillators in Radiation Imaging Detectors. Nucl. Instrum. Methods Phys. Res., Sect. A 2005, 546, 180− 187. (36) Pawade, V. B.; Swart, H. C.; Dhoble, S. J. Review of Rare Earth Activated Blue Emission Phosphors Prepared by Combustion Synthesis. Renewable Sustainable Energy Rev. 2015, 52, 596−612. (37) Bobrov, O. P.; Laptev, S. N.; Khonik, V. A. Isothermal Stress Relaxation of Bulk and Ribbon Pd40Cu30Ni10P20 Metallic Glass. Solid State Phenom. 2006, 115, 121−126. (38) Pawade, V. B.; Dhoble, N. S.; Dhoble, S. J. Promising Blue Emitting Ca3.5Mg0.5Si3O8Cl4: Eu2+ Nanophosphor for Near UV Excited White LEDs. Optoelectron. Adv. Mater: Rapid Commun. 2011, 50, 208−210. (39) Yeh, N.; Chung, J. P. High Brightness LEDs Energy Efficient Lighting Sources and Their Potential in Indoor Plant Cultivation. Renewable Sustainable Energy Rev. 2009, 13, 2175−2180. (40) Yeh, N. G.; Wu, C. H.; Cheng, T. C. Light-emitting Diodes Their Potential in Biomedical Applications. Renewable Sustainable Energy Rev. 2010, 14, 2161−2166. (41) Naczynski, D. J.; Tan, M. C.; Zevon, M.; Wall, B.; Kohl, J.; Kulesa, A.; Chen, S.; Roth, C. M.; Riman, R. E.; Moghe, P. V. Rareearth-doped Biological Composites as in vivo Shortwave Infrared Reporters. Nat. Commun. 2013, 4, 2199. (42) Pawade, V. B.; Dhoble, S. J. Optical Properties of Blue Emitting Ce3+ Activated XMg2Al16O27 (X = Ba, Sr) Phosphors. Opt. Commun. 2011, 284, 4185−4189. (43) Dutta, D. P.; Ghildiyal, R.; Tyagi, A. K. Luminescent Properties of Doped Zinc Aluminate and Zinc Gallate White Light Emitting Nanophosphors Prepared via Sonochemical Method. J. Phys. Chem. C 2009, 113, 16954−16961. (44) Dutta, D. P.; Sudarsan, V.; Srinivasu, P.; Vinu, A.; Tyagi, A. K. Indium Oxide and Europium/ Dysprosium Doped Indium Oxide Nanoparticles: Sonochemical Synthesis, Characterization and Photoluminescence Studies. J. Phys. Chem. C 2008, 112 (17), 6781−6785. (45) Pawade, V. B.; Dhoble, S. J. Novel Blue-emitting SrMg2Al16O27:Eu2+ Phosphor for Solid State Lighting. Lumin. 2011, 26, 722−727. (46) Van der Ende, B. M.; Aarts, L.; Meijerink, A. Lanthanide Ions as Spectral Converters for Solar Cells. Phys. Chem. Chem. Phys. 2009, 11, 11081−11095. 2632

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

(67) McCluskey, M. D.; Jokela, S. J. Defects in ZnO. J. Appl. Phys. 2009, 106, 071101. (68) Vanheusden, K.; Seager, C. H.; Warren, W. L.; Tallant, D. R.; Voigt, J. A. Correlation Between Photoluminescence and Oxygen Vacancies in ZnO Phosphors. Appl. Phys. Lett. 1996, 68, 403. (69) Yang, L. L.; Zhao, Q. X.; Willander, M.; Yang, J. H.; Ivanov, I. Annealing Effects on Optical Properties of Low Temperature Grown ZnO Nanorod Arrays. J. Appl. Phys. 2009, 105, 053503−053507. (70) Djurisic, A. B.; Leung, Y. H.; Tam, K. H.; Hsu, Y. F.; Ding, L.; Ge, W.K.; Zhong, Y. C.; Wong, K. S.; Chan, W. K.; Tam, H. L.; Cheah, K. W.; Kwok, W. M.; Phillips, D. Defect Emissions in ZnO Nanostructures. Nanotechnology 2007, 18, 095702−095710. (71) Djurisic, A. B.; Leung, Y. H.; Tam, K. H.; Ding, L.; Ge, W. K.; Chen, H. Y.; Gwo, S. Green, Yellow and Orange Defect Emission from ZnO Nanostructures: Influence of Excitation Wavelength. Appl. Phys. Lett. 2006, 88, 103107−3. (72) Cao, B.; Cai, W.; Zeng, H. Temperature-dependent Shifts of Three Emission Bands for ZnO Nanoneedle Arrays. Appl. Phys. Lett. 2006, 88, 161101−3. (73) Zeng, H.; Li, Z.; Cai, W.; Liu, P. Strong Localization Effect in Temperature Dependence of Violet-blue Emission from ZnO Nanoshells. J. Appl. Phys. 2007, 102, 104307. (74) Kumar, V.; Swart, H. C.; Ntwaeaborwa, O. M.; Kroon, R. E.; Terblans, J. J.; Shaat, S. K. K.; Yousif, A.; Duvenhage, M. M. Origin of the Red Emission in Zinc Oxide Nanophosphors. Mater. Lett. 2013, 101, 57−60. (75) Kong, Y. C.; Yu, D. P.; Zhang, B.; Fang, W.; Feng, S. Q. Ultraviolet-emitting ZnO Nanowires Synthesized by a Physical Vapor Deposition Approach. Appl. Phys. Lett. 2001, 78, 407−409. (76) Pierce, B. J.; Hengehold, R. L. Depth Resolved Cathodoluminescence of Ion Implanted Layers in Zinc Oxide. J. Appl. Phys. 1976, 47, 644−651. (77) Studenikinm, S. A.; Golegu, N.; Cocivera, M. Fabrication of Green and Orange Photoluminescent Undoped ZnO Films Using Spray Pyrolysis. J. Appl. Phys. 1998, 84, 2287−2294. (78) Bylander, E. G. Surface Effects on the Low Energy Cathodoluminescence of Zinc Oxide. J. Appl. Phys. 1978, 49, 1188− 1195. (79) Wu, X. L.; Siu, G. G.; Fu, C. L.; Ong, H. C. Photoluminescence and Cathodoluminescence Studies of Stoichiometric and Oxygendeficient ZnO Films. Appl. Phys. Lett. 2001, 78, 2285−2287. (80) Wu, L.; Wu, Y.; Pan, X.; Kong, F. Synthesis of ZnO Nanorod and the Annealing Effect on its Photoluminescence Property. Opt. Mater. 2006, 28, 418−422. (81) Chen, M.; Wang, X.; Yu, Y. H.; Pei, Z. L.; Bai, X. D.; Sun, C.; Huang, R. F.; Wen, L. S. X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy Studies of Al-doped ZnO Films. Appl. Surf. Sci. 2000, 158, 134−140. (82) Kim, Y. S.; Tai, W. P.; Shu, S. J. Effect of Preheating Temperature on Structural and Optical Properties of ZnO Thin Films by Sol-gel Process. Thin Solid Films 2005, 491, 153−160. (83) Islam, M. N.; Ghosh, T. B.; Chopra, K. L.; Acharya, H. N. XPS and X-ray diffraction Studies of Aluminum-doped Zinc Oxide Transparent Conducting Films. Thin Solid Films 1996, 280, 20−25. (84) Kumar, V.; Swart, H. C.; Gohain, M.; Kumar, V.; Som, S.; Bezuindenhoudt, B. C. B.; Ntwaeaborwa, O. M. Influence of Ultrasonication Times on the Tunable Colour Emission of ZnO Nanophosphors for Lighting Applications. Ultrason. Sonochem. 2014, 21, 1549−1556. (85) Singh, T.; Pandya, D. K.; Singh, R. Surface Plasmon Driven Enhancement in UV Emission of Electrochemically Grown Zn1‑xCdxO Nanorods using Au Nanoparticles. J. Alloys Compd. 2013, 552, 294− 298. (86) Huang, M. H.; Wu, Y.; Feick, H.; Tran, N.; Weber, E.; Yang, P. Catalytic Growth of Zinc Oxide Nanowires by Vapour Transport. Adv. Mater. 2001, 13, 113−116. (87) Monticone, S.; Tufeu, R.; Kanaev, A. V. Complex Nature of the UV and Visible Fluorescence of Colloidal ZnO Nanoparticles. J. Phys. Chem. B 1998, 102, 2854−2862.

(47) Liu, H.; Yang, J.; Wang, Y.; Wei, M.; Zhang, Y. Ferromagnetism and Exchange Bias in Fe Doped ZnO Nanocrystals. Mater. Chem. Phys. 2008, 112, 1021−1023. (48) Toyama, T.; Takeuchi, H.; Yamaguchi, D.; Kawasaki, H.; Itatani, K.; Okamoto, H. Solution Processed ZnO Nanocrystals in Thin-film Light-emitting Diodes for Printed Electronics. J. Appl. Phys. 2010, 108, 084302. (49) Chen, L.; Zhang, J.; Luo, Y.; Lu, S.; Wang, X. Effect of Zn2+ and Mn2+ Introduction on the Luminescent Properties of Colloidal ZnS:Mn2+ Nanoparticles. Appl. Phys. Lett. 2004, 84, 112. (50) Bhargava, R. N. Doped Nanocrystalline Materials Physics and Applications. J. Lumin. 1996, 70, 85−94. (51) Kumar, V.; Swami, S. K.; Kumar, A.; Ntwaeaborwa, O. M.; Dutta, V.; Swart, H. C. Eu3+ Doped Down Shifting TiO2 Layer for Efficient Dye-sensitized Solar Cells. J. Colloid Interface Sci. 2016, 484, 24−32. (52) Zeng, X.; Yuan, J.; Zhang, L. Synthesis and Photoluminescent Properties of Rare Earth Doped ZnO Hierarchical Microspheres. J. Phys. Chem. C 2008, 112, 3503. (53) Dorenbos, P.; van der Kolk, E. Location of Lanthanide Impurity Levels in the III-V Semiconductor GaN. Appl. Phys. Lett. 2006, 89, 061122. (54) John, R.; Rajakumari, R. Synthesis and Characterization of Rare Earth Ion Doped Nano ZnO. Nano-Micro Lett. 2012, 4 (2), 65−72. (55) Yao, N.; Huang, J.; Fu, K.; Deng, X.; Ding, M.; Shao, M.; Xu, X. Enhanced Light Harvesting of Dye-sensitized Solar Cells with Up/ down Conversion Materials. Electrochim. Acta 2015, 154, 273−277. (56) Silambarasan, M.; Saravanan, S.; Ohtani, N.; Soga, T. Structural and Optical Studies of Pure and Ni doped ZnO Nanoparticles Synthesized by Simple Solution Combustion Method. Jpn. J. Appl. Phys. 2014, 53, 05FB16. (57) Kumar, V.; Ntwaeaborwa, O. M.; Holsa, J.; Motaung, D.E.; Swart, H. C. The Role of Oxygen and Titanium Related Defects on the Emission of TiO2:Tb3+ Nano-phosphor for Blue Lighting Applications. Opt. Mater. 2015, 46, 510−516. (58) Yin, X.; Wang, B.; He, M.; He, T. Facile Synthesis of ZnO Nanocrystals via a Solid State Reaction for High Performance Plastic Dye-sensitized Solar Cells. Nano Res. 2012, 5 (1), 1−10. (59) Ali, A. G.; Dejene, F. B.; Swart, H. C. Effect of Mn Doping on the Structural and Optical Properties of Sol-gel Derived ZnO Nanoparticles. Cent. Eur. J. Phys. 2012, 10 (2), 478−484. (60) Dejene, F. B.; Ali, A. G.; Swart, H. C.; Botha, R. J.; Roro, K.; Coetsee, L.; Biggs, M. M. Optical Properties of ZnO Nanoparticles Synthesized by Varying the Sodium Hydroxide to Zinc Acetate Molar Ratios Using a Sol-Gel Process. Cent. Eur. J. Phys. 2011, 9 (5), 1321− 1326. (61) Layek, A.; Banerjee, S.; Manna, B.; Chowdhury, A. Synthesis of Rare-earth Doped ZnO Nanorods and Their Defect-dopant Correlated Enhanced Visible Orange Luminescence. RSC Adv. 2016, 6, 35892−900. (62) Wang, M.; Huang, C.; Huang, Z.; Guo, W.; Huang, J.; He, H.; Wang, H.; Cao, Y.; Liu, Q.; Liang, J. Synthesis and Photoluminescence of Eu-doped ZnO Microrods Prepared by Hydrothermal Method. Opt. Mater. 2009, 31, 1502−1505. (63) Koao, L. F.; Dejene, F. B.; Swart, H. C.; Botha, J. R. The Effect of Ce3+ on Structure, Morphology and Optical Properties of Flower Like ZnO Synthesized using the Chemical Bath Method. J. Lumin. 2013, 143, 463−468. (64) Lu, X.; Liu, Z.; Zhu, Y.; Jiang, L. Sonochemical Synthesis and Photocatalytic Property of Zinc Oxide Nanoparticles Doped with Magnesium (II). Mater. Res. Bull. 2011, 46, 1638−1641. (65) Zhou, H.; Yi, D.; Yu, Z.; Xiao, L.; Li, J. Preparation of Aluminum Doped Zinc Oxide Films and the Study of Their Microstructure, Electrical and Optical Properties. Thin Solid Films 2007, 515, 6909− 6914. (66) Dwivedi, C.; Dutta, V. Effect of Seed Layer on the Self-assembly of Spray Pyrolyzed Al Doped ZnO Nanoparticles. AIP Adv. 2013, 3, 032127. 2633

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

(88) Ahn, C. H.; Kim, Y. Y.; Kim, D. C.; Mohanta, S. K.; Cho, H. K. A Comparative Analysis of Deep Level Emission in ZnO Layers Deposited by Various Methods. J. Appl. Phys. 2009, 105, 013502. (89) Lee, S. H.; Park, J. H.; Son, S. M.; Kim, J. S.; Park, H. L. Whitelight-emitting Phosphor CaMgSi2O6: Eu2+Mn2+ and its Related Properties with Blending. Appl. Phys. Lett. 2006, 89, 221916. (90) Alvi, N. H.; Hasan, K.; Nur, O.; Willander, M. The Origin of the Red Emission in n-ZnO Nanotubes/p-GaN White Light Emitting Diodes. Nanoscale Res. Lett. 2011, 6, 130. (91) Ahn, C. H.; Kim, Y. Y.; Kim, D. C.; Mohanta, S. K.; Cho, H. K. A Comparative Analysis of Deep Level Emission in ZnO Layers Deposited by Various Methods. J. Appl. Phys. 2009, 105, 089902− 089901. (92) Bunzli, J. C. G. Benefiting from the Unique Properties of Lanthanide Ions. Acc. Chem. Res. 2006, 39, 53−61. (93) Auzel, F. Upconversion and Anti-stokes Processes with f and d Ions in Solids. Chem. Rev. 2004, 104, 139−173. (94) Bunzli, J. C. Z.; Piguet, C. Taking Advantage of Luminescent Lanthanide Ions. Chem. Soc. Rev. 2005, 34, 1048−1077. (95) Eliseeva, S.; Bunzli, J. C. G. Lanthanide Luminescence for Functional Materials and Bio-sciences. Chem. Soc. Rev. 2010, 39, 189− 227. (96) Díaz-Herrera, B.; Jiménez-Rodríguez, E.; Gonzalez-Diaz, B.; Montesdeoca-Santana, A.; Velázquez, J. J.; Guerrero-Lemus, R. Combined Upconversion, Downconversion and Down Shifting Photo-luminescence of Low Cost Erbium-ytterbium Co-doped Porous Silicon Produced by Stain Etching. Thin Solid Films 2011, 519, 6110− 6114. (97) Trupke, T.; Green, M. A.; Wurfel, P. Improving Solar Cell Efficiencies by Down-Conversion of High Energy Photons. J. Appl. Phys. 2002, 92, 1668. (98) Shalav, A.; Richards, B. S.; Green, M. A. Luminescent Layers for Enhanced Silicon Solar Cell Performance: Up-conversion. Sol. Energy Mater. Sol. Cells 2007, 91, 829−842. (99) Trupke, T.; Green, M. A.; Wurfel, P. Improving Solar Cell Efficiencies by Upconversion of Sub-band Gap Light. J. Appl. Phys. 2002, 92, 4117. (100) Stehr, J. E.; Chen, S. L.; Reddy, N. K.; Tu, C. W.; Chen, W. M.; Buyanova, I. A. Turning ZnO into an Efficient Energy Upconversion Material by Defect Engineering. Adv. Funct. Mater. 2014, 24, 3760− 3764. (101) Klampaftis, E.; Ross, D.; McIntosh, K. R.; Richards, B. S. Enhancing the Performance of Solar Cells via Luminescent Downshifting of the Incident Spectrum: A Review. Sol. Energy Mater. Sol. Cells 2009, 93, 1182−1194. (102) Dexter, D. Possibility of Luminescent Quantum Yields Greater than Unity. Phys. Rev. 1957, 108 (3), 630−633. (103) Piper, W.; DeLuca, J.; Ham, F. Cascade Fluorescent Decay in Pr3+ Doped Fluorides: Achievement of a Quantum Yield Greater than Unity for Emission of Visible Light. J. Lumin. 1974, 8, 344−348. (104) Sommerdijk, J.; Bril, A.; de Jager, A. Two Photon Luminescence with Ultraviolet Excitation of Trivalent Praseodymium. J. Lumin. 1974, 8, 341−343. (105) van der Kolk, E.; Dorenbos, P.; van Eijk, C. Vacuum Ultraviolet Excitation and Quantum Splitting of Pr3+ in LaZrF7 and αLaZr3F15. Opt. Commun. 2001, 197, 317−326. (106) Srivastava, A.; Beers, W. Luminescence of Pr3+ in SrAl12O19: Observation of Two Photon Luminescence in Oxide Lattice. J. Lumin. 1997, 71, 285−290. (107) Wegh, R.; Donker, H.; Loef, E.; Oskam, K.; Meijerink, A. Quantum Cutting Through Down Conversion in Rare-earth Compounds. J. Lumin. 2000, 87−89, 1017−1019. (108) Feldmann, C.; Justel, T.; Ronda, C.; Wiechert, D. Quantum Efficiency of Down Conversion Phosphor LiGdF4:Eu. J. Lumin. 2001, 92, 245−254. (109) Oskam, K.; Wegh, R.; Donker, H.; Loef, E.; Meijerink, A. Downconversion: A New Route to Visible Quantum cutting. J. Alloys Compd. 2000, 300−301, 421−425.

(110) Berkowitz, J.; Olsen, J. Investigation of Luminescent Materials Under Ultraviolet Excitation Energies from 5 to 25 eV. J. Lumin. 1991, 50, 111. (111) Ilmas, E.; Savikhina, T. Investigation of Luminescence Excitation Processes in Some Oxygen-dominated Compounds by 3 to 21 eV photons. J. Lumin. 1970, 1 (2), 702−715. (112) Steckl, J.; Park, J. H.; Zavada, J. M. Prospects for Rare Earth Doped GaN Lasers on Si. Mater. Today 2007, 10, 20−27. (113) Godlewski, M.; Leskela, M. Excitation and Recombination Processes During Electroluminescence of Rare Earth Activated Materials. Crit. Rev. Solid State Mater. Sci. 1994, 19, 199−239. (114) Ennen, H.; Schneider, J.; Pomrenke, G.; Axmann, A. 1.54 μm Luminescence of Erbium-implanted III-V Semiconductors and Silicon. Appl. Phys. Lett. 1983, 43, 943. (115) Ennen, H.; Pomrenke, G.; Axmann, A.; Eisele, K.; Haydl, W.; Schneider, J. 1.54 μm Electroluminescence of Erbium Doped Silicon Grown by Molecular Beam Epitaxy. Appl. Phys. Lett. 1985, 46, 381. (116) Koao, L. F.; Dejene, F. B.; Kroon, R. E.; Swart, H. C. Effect of Eu3+ on the Structure, Morphology and Optical Properties of Flowerlike ZnO Synthesized using Chemical Bath Deposition. J. Lumin. 2014, 147, 85−89. (117) Koao, L. F.; Dejene, F. B.; Swart, H. C.; Botha, J. R. The Effect of Ce3+ on Structure, Morphology and Optical Properties of Flowerlike ZnO Synthesized using the Chemical Bath Method. J. Lumin. 2013, 143, 463−468. (118) Alvi, N. H.; ul Hasan, K.; Nur, O.; Willander, M. The Origin of the Red Emission in n-ZnO Nanotubes/p-GaN White Light Emitting Diodes. Nanoscale Res. Lett. 2011, 6, 130. (119) Omata, T.; Ueda, N.; Ueda, K.; et al. New Oxide Phase with Wide Band Gap and High Electroconductivity CdGa2O4 Spinel. Appl. Phys. Lett. 1993, 62, 499. (120) Barros, B. S.; Melo, P. S.; Kiminami, R. H. G. A.; Costa, A. C. F. M.; Sa, G. F.; Alves, S., Jr. Photophysical Properties of Eu3+ and Tb3+ Doped ZnAl2O4 Phosphors Obtained by Combustion Reaction. J. Mater. Sci. 2006, 41, 4744−4748. (121) Xu, Y.; Zhang, X.; Dai, S.; Fan, B.; Ma, H.; et al. Efficient NIR Down Conversion in Pr3+-Yb3+ Co-doped Glasses and Glass Ceramics Containing LaF3 Nanocrystals. J. Phys. Chem. C 2011, 115 (26), 13056−13062. (122) Liang, X.; Yang, Y.; Zhu, C.; Yuan, S.; Chen, G.; et al. PL Properties of Tb3+-Sm3+ Co-doped Glasses for White Light Emitted Diodes. Appl. Phys. Lett. 2007, 91, 091104. (123) Zhu, C.; Liang, X.; Yang, Y.; Chen, G. Luminescence Properties of Tb Doped and Tm/Tb/Sm Co-doped Glasses for LED Applications. J. Lumin. 2010, 130, 74−77. (124) Zhao, S.; Wang, L.; Yang, L.; Wang, Z. Synthesis and Luminescence Properties of ZnO:Tb3+ Nanotube Arrays via Electrodeposited Method. Phys. B 2010, 405, 3200−3204. (125) Lin, J.; Huang, Y.; Zhang, J.; Gao, J.; Ding, X.; Huang, Z.; Tang, C.; et al. Characterization and Photoluminescence Properties of Tb Doped SiO2 Nanowires as a Novel Green-Emitting Phosphor. Chem. Mater. 2007, 19, 2585. (126) Li, G.; Lu, X.; Su, C.; Tong, Y. Facile Synthesis of Hierarchical ZnO:Tb3+ Nanorod Bundles and Their Optical and Magnetic Properties. J. Phys. Chem. C 2008, 112, 2927−2933. (127) Kumar, V.; Som, S.; Kumar, V.; Kumar, V.; Ntwaeaborwa, O. M.; Coetsee, E.; Swart, H. C. Tunable and White Emission from ZnO:Tb3+ Nanophosphors for Solid State Lighting Applications. Chem. Eng. J. 2014, 255, 541−552. (128) Ahn, C.; Kim, Y. Y.; Kim, D. C.; Mohanta, S. K.; Cho, H. K. A Comparative Analysis of Deep Level Emission in ZnO Layers Deposited by Various Methods. J. Appl. Phys. 2009, 105, 013502. (129) Pereira, A. S.; Peres, M.; Soares, M. J.; Alves, E.; Neves, A.; Monteiro, T.; Trindade, T. Synthesis, Surface Modification and Optical Properties of Tb3+ Doped ZnO Nanocrystals. Nanotechnology 2006, 17, 834. (130) Dexter, D. L.; Schulman, J. H. Theory of Concentration Quenching in Inorganic Phosphors. J. Chem. Phys. 1954, 22, 1063. 2634

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

(151) Panda, R.; Acharya, B. S.; Singh, T. B.; Gartia, R. K. Luminescence Properties and Decay Kinetics of Nano ZnO Powder Doped with Cerium Ions. J. Lumin. 2013, 136, 369−377. (152) Shi, Q.; Wang, C.; Li, S.; Wang, Q.; Zhang, B.; Wang, W.; Zhang, J.; Zhu, H. Enhancing Blue Luminescence from Ce-doped ZnO Nanophosphor by Li Doping. Nanoscale Res. Lett. 2014, 9, 480. (153) Ntwaeaborwa, O. M.; Holloway, P. H. Enhanced Photoluminescence of Ce3+ Induced by an Energy Transfer from ZnO Nanoparticles Encapsulated in SiO2. Nanotechnology 2005, 16, 865− 868. (154) Sommerdijk, J. L.; Bril, A. Efficiency of Dy3+ Activated Phosphors. J. Electrochem. Soc. 1975, 122, 952−954. (155) Yu, M.; Lin, J.; Wang, Z.; Fu, J.; Wang, S.; Zhang, H. J.; Han, Y. C. Fabrication, Patterning and Optical Properties of Nanocrystalline YVO4:A (A = Eu3+, Dy3+, Sm3+, Er3+) Phosphor Films via Sol-gel Soft Lithography. Chem. Mater. 2002, 14, 2224−2231. (156) Gu, F.; Wang, S. F.; Lu, M. K.; Zhou, G. J.; Xu, D.; Yuan, D. R. Structure Evaluation and Highly Enhanced Luminescence of Dy3+Doped ZnO Nanocrystals by Li+ Doping via Combustion Method. Langmuir 2004, 20, 3528−3531. (157) Jayachandraiah, C.; Kumar, K. S.; Krishnaiah, G.; Rao, N. M. Influence of Dy Dopant on Structural and Photoluminescence of Dy Doped ZnO Nanoparticles. J. Alloys Compd. 2015, 623, 248−254. (158) Riwotzki, K.; Haase, M. Wet Chemical Synthesis of Doped Colloidal Nanoparticles: YVO4:Ln (Ln = Eu, Sm, Dy). J. Phys. Chem. B 1998, 102, 10129−10135. (159) Lin, C. C.; Young, S. L.; Kung, C. Y.; Horng, L.; Chen, H. Z.; Kao, M. C.; Shih, Y. T.; Ou, C. R. Phonon Spectra and Magnetic Behaviors of Hydrothermally Synthesized Sm Doped ZnO Nanorods. Vacuum 2013, 87, 178−181. (160) Venkatesan, D.; Deepan, D.; Velavan, M.; Sankar, R.; Jayavel, R.; Dhanasekaran, R. Preparation and Characterization of Rare Earth (Pr, Nd) Doped ZnO Nanoparticles. International Conference on Nanoscience and Nanotechnology 2010, 343−347. (161) Rani, S.; Lal, B.; Saxena, S.; Shukla, S. Photoluminescence Properties of Gd:ZnO Nanophosphor. J. Sol-Gel Sci. Technol. 2017, 81, 586−592. (162) Bloembergen, N. Solid State Quantum Counters. Phys. Rev. Lett. 1959, 2, 84−85. (163) Wang, F.; Liu, X. G. Recent Advances in the Chemistry of Lanthanide Doped Upconversion Nanocrystals. Chem. Soc. Rev. 2009, 38, 976−989. (164) Downing, E.; Hesselink, L.; Ralston, J.; Macfarlane, R. A Three Color, Solid State, Three Dimensional Display. Science 1996, 273, 1185−89. (165) Silversmith, A. J.; Lenth, W.; Macfarlane, R. M. Green Infrared Pumped Erbium Upconversion Laser. Appl. Phys. Lett. 1987, 51, 1977−1979. (166) Sandrock, T.; Scheife, H.; Heumann, E.; Huber, G. High Power Continuous Wave Upconversion Fiber Laser at Room Temperature. Opt. Lett. 1997, 22, 808−810. (167) Suyver, J. F.; Aebischer, A.; Biner, D.; Gerner, P.; Grimm, J.; et al. Novel Materials Doped with Trivalent Lanthanides and Transition Metal Ions Showing Near Infrared to Visible Photon Upconversion. Opt. Mater. 2005, 27, 1111−1130. (168) Gai, S. L.; Li, C. X.; Yang, P. P.; Lin, J. Recent Progress in Rare Earth Micro/ Nanocrystals: Soft Chemical Synthesis, Luminescent Properties and Biomedical Applications. Chem. Rev. 2014, 114, 2343− 2389. (169) Li, X. M.; Zhang, F.; Zhao, D. Y. Highly Efficient Lanthanide Upconverting Nanomaterials: Progress and Challenges. Nano Today 2013, 8, 643−676. (170) Shen, J.; Sun, L. D.; Yan, C. H. Luminescent Rare Earth Nanomaterials for Bioprobe Applications. Dalton Trans. 2008, 5687− 99. (171) Gu, Z. J.; Yan, L.; Tian, G.; Li, S. J.; Chai, Z. F.; Zhao, Y. Recent Advantages in Design and Fabrication of Upconversion Nanoparticles and their Safe Theranostic Applications. Adv. Mater. 2013, 25, 3758−3779.

(131) Bylander, E. G. Surface Effects on the Low Energy Cathodoluminescence of Zinc Oxide. J. Appl. Phys. 1978, 49, 1188. (132) Wu, X. L.; Siu, G. G.; Fu, C. L.; Ong, H. C. Photoluminescence and Cathodoluminescence Studies of Stoichiometric and Oxygen Deficient ZnO Films. Appl. Phys. Lett. 2001, 78, 2285. (133) Wu, L.; Wu, Y.; Pan, X.; Kong, F. Synthesis of ZnO Nanorod and The Annealing Effect on its Photoluminescence Property. Opt. Mater. 2006, 28, 418−422. (134) Kabongo, G. L.; Mhlongo, G. H.; Malwela, T.; Mothudi, B. M.; Hillie, K. T.; Dhlamini, M. S. Microstructural and Photoluminescence Properties of Sol-gel Derived Tb3+ Doped ZnO Nanocrystals. J. Alloys Compd. 2014, 591, 156−163. (135) Singh, N. S.; Singh, S. D.; Meetei, S. D. Structural and Photoluminescence Properties of Terbium Doped Zinc Oxide Nanoparticles. Chin. Phys. B 2014, 23 (5), 058104. (136) Gao, S.; Zhang, H.; Deng, R.; Wang, X.; Sun, D.; Zheng, G. Engineering White Light Emitting Eu-doped ZnO Urchins by Biopolymer Assisted Hydrothermal Method. Appl. Phys. Lett. 2006, 89, 123125. (137) Park, J. H.; Steckl, A. J. Demonstration of a Visible Laser on Silicon using Eu-doped GaN Thin Films. J. Appl. Phys. 2005, 98, 056108. (138) Kumar, V.; Kumar, V.; Som, S.; Duvenhage, M. M.; Ntwaeaborwa, O. M.; Swart, H. C. Effect of Eu doping on the Photoluminescence Properties of ZnO Nanophosphors for Red Emission Applications. Appl. Surf. Sci. 2014, 308, 419−430. (139) Du, Y. P.; Zhang, Y. W.; Sun, L. D.; Yan, C. H. Efficient Energy Transfer in Monodisperse Eu-doped ZnO Nanocrystals Synthesized from Metal Acetylacetonates in High-boiling Solvents. J. Phys. Chem. C 2008, 112, 12234−12241. (140) Aneesh, P. M.; Jayaraj, M. K. Red Luminescence from Hydrothermally Synthesized Eu Doped ZnO Nanoparticles under Visible Excitation. Bull. Mater. Sci. 2010, 33 (3), 227−231. (141) Shahroosvand, H.; Ghorbani-asl, M. Solution-based Synthetic Strategies for Eu Doped ZnO Nanoparticle with Enhanced Red Photoluminescence. J. Lumin. 2013, 144, 223−229. (142) Ishizumi, A.; Kanemitsu, Y. Structural and Luminescence Properties of Eu-doped ZnO Nanorods Fabricated by a Microemulsion Method. Appl. Phys. Lett. 2005, 86, 253106. (143) Dorenbos, P. The 5d Level Positions of the Trivalent Lanthanides in Inorganic Compounds. J. Lumin. 2000, 91, 155−176. (144) Liao, L.; Mai, H. X.; Yuan, Q.; Lu, H. B.; Li, J. C.; Liu, C.; Yan, C. H.; Shen, Z. X.; Yu, T. Single CeO2 Nanowire Gas Sensor Supported with Pt Nanocrystals: Gas Sensitivity, Surface Bond States and Chemical Mechanism. J. Phys. Chem. C 2008, 112, 9061−9065. (145) Luo, Q.; Wang, L. S.; Guo, H. Z.; Lin, K. Q.; Chen, Y.; Yue, G. H.; Peng, D. L. Blue Luminescence from Ce-doped ZnO Thin Films Prepared by Magnetron Sputtering. Appl. Phys. A: Mater. Sci. Process. 2012, 108, 239−245. (146) Motloung, S. V.; Dejene, F. B.; Kroon, R. E.; Swart, H. C.; Ntwaeaborwa, O. M. Radiative Energy Transfer in ZnAl2O4:0.1% Ce3+, x% Eu3+ Nanophosphor Synthesized by Sol-gel Process. Phys. B 2015, 468−469, 11−20. (147) Koao, L. F.; Dejene, F. B.; Tsega, M.; Swart, H. C. Annealed Ce3+ Doped ZnO Flower-like Morphology Synthesized by Chemical Bath Deposition Method. Phys. B 2016, 480, 53−57. (148) Aravind, A.; Jayaraj, M. K.; Kumar, M.; Chandra, R. Optical and Magnetic Properties of Copper Doped ZnO Nanorods Prepared by Hydrothermal Method. J. Mater. Sci.: Mater. Electron. 2013, 24, 106−112. (149) Willander, M.; Nur, O.; Sadaf, J. R.; Qadir, M. I.; Zaman, S.; Zainelabdin, A.; Bano, N.; Hussain, I. Luminescence from Zinc Oxide Nanostructures and Polymers and their Hybrid Devices. Materials 2010, 3, 2643−2667. (150) Shukla, S. K.; Agorku, E. S.; Mittal, H.; Mishra, A. K. Synthesis, Characterization and Photoluminescence Properties of Ce3+ Doped ZnO Nanophosphors. Chem. Pap. 2014, 68 (2), 217−222. 2635

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

(192) Yang, J.; Zhang, H.; Wang, X.; et al. Optical Properties of Er3+Ag Co-doped ZnO Nanocrystals Prepared by Combustions Method. J. Mater. Sci.: Mater. Electron. 2014, 25, 3895−3900. (193) Liu, Y.; Luo, W.; Li, R.; Zhu, H.; Chen, X. Near-infrared Luminescence of Nd3+ and Tm3+ ions Doped ZnO Nanocrystals. Opt. Express 2009, 17 (2), 9748−9753. (194) Balestrieri, M.; Ferblantier, G.; Colis, S.; Schmerber, G.; UlhaqBouillet, C.; Muller, D.; Slaoui, A.; Dinia, A. Structural and Optical Properties of Yb-doped ZnO Films Deposited by Magnetron Reactive Sputtering for Photon Conversion. Sol. Energy Mater. Sol. Cells 2013, 117, 363−371. (195) Soumahoro, I.; Schmerber, G.; Douayar, A.; Colis, S.; AbdLefdil, M.; Hassanain, N.; Berrada, A.; Muller, D.; Slaoui, A.; Rinnert, H.; Dinia, A. Structural, Optical and Electrical Properties of Yb Doped ZnO Thin Films Prepared by Spray Pyrolysis Method. J. Appl. Phys. 2011, 109, 033708. (196) Shestakov, M. V.; Baranov, A. N.; Tikhomirov, V. K.; Zubavichus, Y. V.; Kuznetsov, A. S.; Veligzhanin, A. A.; Kharin, A. Y.; Rösslhuber, R.; Timoshenko, V. Y.; Moshchalkov, V. V. Energy Transfer Luminescence of a Zinc Oxide/Ytterbium Oxide Nanocomposite. RSC Adv. 2012, 2, 8783−8788. (197) Luo, Q.; Qiao, X.; Fan, X.; Zhang, X. Near-infrared Emission of Yb3+ Through Energy Transfer from ZnO to Yb3+ in Glass Ceramic Containing ZnO Nanocrystals. Opt. Lett. 2011, 36, 2767−2769. (198) Kabongo, G. L.; Mhlongo, G. H.; Mothudi, B. M.; Hillie, K. T.; Swart, H. C.; Dhlamini, M. S. Enhanced Exciton emission from ZnO Nano-phosphor Induced by Yb3+ Ions. Mater. Lett. 2014, 119, 71−74. (199) Bai, Y.; Wang, Y.; Yang, K.; Zhang, X.; Song, Y.; Wang, C. H. Enhanced Upconverted Photoluminescence in Er3+ and Yb3+ Codoped ZnO Nanocrystals With and Without Li+ Ions. Opt. Commun. 2008, 281, 5448−5452. (200) Salley, G. M.; Valiente, R.; Gudel, H. U. Luminescence Upconversion Mechanisms in Yb3+-Tb3+ Systems. J. Lumin. 2001, 94, 305−309. (201) Shockley, W.; Queisser, H. J. Detailed Balance Limit of Efficiency of p-n Junction Solar Cells. J. Appl. Phys. 1961, 32 (3), 510. (202) Zhou, H.; Qu, Y.; Zeid, T.; Duan, X. Towards Highly Efficient Photocatalysts using Semiconductor Nanoarchitectures. Energy Environ. Sci. 2012, 5, 6732. (203) Zhang, Q. Y.; Huang, X. Y. Recent Progress in Quantum Cutting Phosphors. Prog. Mater. Sci. 2010, 55, 353−427. (204) Chander, N.; Khan, A. F.; Komarala, V. K.; Chawla, S.; Dutta, V. Enhancement of Dye Sensitized Solar Cell Efficiency via Incorporation of Upconverting Phosphor Nanoparticles as Spectral Converters. Prog. Photovoltaics 2016, 24, 692−703. (205) Chander, N.; Khan, A. F.; Komarala, V. K. Improved Stability and Enhanced Efficiency of Dye Sensitized Solar Cells by Using Europium Doped Yttrium Vanadate Down Shifting Nanophosphor. RSC Adv. 2015, 5, 66057. (206) Chander, N.; Khan, A. F.; Chandrasekhar, P. S.; Thouti, E.; Swami, S. K.; Dutta, V.; Komarala, V. K. Reduced Ultraviolet Light Induced Degradation and Enhanced Light Harvesting using YVO4: Eu3+ Down Shifting Nano-phosphor Layer in Organometal Halide Perovskite Solar Cells. Appl. Phys. Lett. 2014, 105, 033904. (207) Chander, N.; Sardana, S. K.; Parashar, P. K.; Khan, A. F.; Chawla, S.; Komarala, V. K. Improving the Short-Wavelength Spectral Response of Silicon Solar Cells by Spray Deposition of YVO4:Eu3+ Downshifting Phosphor Nanoparticles. IEEE J. of Photovoltaics 2015, 5, 1373. (208) Liu, J.; Wang, G.; Luo, K.; He, X.; Ye, Q.; Liao, C.; Mei, J. Understanding the Role of the Electron Transport Layer in Highly Efficient Planar Perovskite Solar Cells. ChemPhysChem 2017, 18, 617− 625. (209) Singh, T.; Singh, J.; Miyasaka, T. Role of Metal Oxide Electron Transport Layer Modification on the Stability of High Performing Perovskite Solar Cells. ChemSusChem 2016, 9, 2559. (210) Wu, N.; Luo, Q.; Qiao, X.; Ma, C.-Q. The Preparation of a Eu3+ Doped ZnO Bi-functional Layer and its Application in Organic Photovoltaics. Mater. Res. Express 2015, 2, 125901.

(172) Huang, X. Y.; Han, S. Y.; Huang, W.; Liu, X. Enhancing Solar Cell Efficiency: the Search for Luminescent Materials as Spectral Converters. Chem. Soc. Rev. 2013, 42, 173−201. (173) Idris, N. M.; Jayakumar, M. K. G.; Bansal, A.; Zhang, Y. Upconversion Nanoparticles as Versatile Light Nanotransducers for Photoactivation Applications. Chem. Soc. Rev. 2015, 44, 1449. (174) Pandey, A.; Rai, V. K.; Kumar, V.; Kumar, V.; Swart, H. C. Upconversion Based Temperature Sensing Ability of Er3+-Yb3+ Codoped SrWO4: An Optical Heating Phosphor. Sens. Actuators, B 2015, 209, 352−358. (175) Patra, A.; Friend, C. S.; Kapoor, R.; Prasad, P. N. Upconversion in Er3+:ZrO2 Nanocrystals. J. Phys. Chem. B 2002, 106, 1909−1912. (176) Patra, A.; Friend, C. S.; Kapoor, R.; Prasad, P. N. Fluorescence Upconversion Properties of Er3+ Doped TiO2 and BaTiO3 Nanocrystallites. Chem. Mater. 2003, 15, 3650−3655. (177) Capobianco, J. A.; Vetrone, F.; Boyer, J. C.; Speghini, A.; Bettinelli, M. Enhancement of Red Emission (4F9/2 → 4I15/2) via Upconversion in Bulk and Nanocrystalline Cubic Y2O3:Er3+. J. Phys. Chem. B 2002, 106, 1181−1187. (178) Vetrone, F.; Boyer, J. C.; Capobianco, J. A.; Speghini, A.; Bettinelli, M. Effect of Yb3+ Codoping on the Upconversion Emission in Nanocrystalline Y2O3:Er3+. J. Phys. Chem. B 2003, 107, 1107−1112. (179) Vetrone, F.; Boyer, J. C.; Capobianco, J. A.; Speghini, A.; Bettinelli, M. Concentration Dependent Near Infrared to Visible Upconversion in Nanocrystalline and Bulk Y2O3:Er3+. Chem. Mater. 2003, 15, 2737−2743. (180) Tessari, G.; Bettinelli, M.; Speghini, A.; Ajo, D.; Pozza, G.; Depero, L. E.; Allieri, B.; Sangaletti, L. Synthesis and Optical Properties of Nanosized Powders: Lanthanide Doped Y2O3. Appl. Surf. Sci. 1999, 144−145, 686−689. (181) Vetrone, F.; Boyer, J. C.; Capobianco, J. A.; et al. NIR to visible Upconversion in Nanocrystalline and Bulk Lu2O3:Er3+. J. Phys. Chem. B 2002, 106, 5622. (182) Capobianco, J. A.; Vetrone, F.; Boyer, J. C.; Speghini, A.; Bettinelli, M. Visible Upconversion of Er3+ Doped Nanocrystalline and Bulk Lu2O3. Opt. Mater. 2002, 19, 259−268. (183) Zhang, H. X.; Kam, C. H.; Zhou, Y.; Han, X. Q.; Buddhudu, S.; Lam, Y. L. Visible Upconversion Luminescence in Er3+:BaTiO3 Nanocrystals. Opt. Mater. 2000, 15, 47−50. (184) Yi, G.; Sun, B.; Yang, F.; Chen, D.; Zhou, Y.; Cheng, J. Synthesis and Characterization of High Efficiency Nanocrystal Upconversion Phosphors: Ytterbium and Erbium Codoped Lanthanum Molybdate. Chem. Mater. 2002, 14, 2910. (185) Bahtat, A.; Bouazaoui, M.; Bahtat, M.; Garapon, C.; Jacquier, B.; Mugnier, J. Upconversion Fluorescence Spectroscopy in Er3+:TiO2 Planar Waveguides Prepared by a Sol-gel Process. J. Non-Cryst. Solids 1996, 202, 16−22. (186) Schmidt, T.; Muller, G.; Spanhel, L.; Kerkel, K.; Forchel, A. Activation of 1.54 μm Er3+ Fluorescence in Concentrated II−VI Semiconductor Cluster Environments. Chem. Mater. 1998, 10, 65−71. (187) Kohls, M.; Bonanni, M.; Spanhel, L.; Su, D. S.; Giersig, M. Green ErIII Luminescence in Fractal ZnO Nanolattices. Appl. Phys. Lett. 2002, 81, 3858. (188) Wang, X.; Kong, X.; Shan, G.; Yu, Y.; Sun, Y.; Feng, L.; Chao, K.; Lu, S.; Li, Y. Luminescence Spectroscopy and Visible Upconversion Properties of Er3+ in ZnO Nanocrystals. J. Phys. Chem. B 2004, 108, 18408−18413. (189) Das, R.; Khichar, N.; Chawla, S. Dual Mode Luminescence in Rare Earth (Er3+/Ho3+) Doped ZnO Nanoparticles Fabricated by Inclusive Coprecipitation Technique. J. Mater. Sci.: Mater. Electron. 2015, 26, 7174−7182. (190) Tsuda, M.; Soga, K.; Inoue, S.; Makishima, A.; Inoue, H. Upconversion Mechanism in Er3+ Doped Fluorozirconate Glasses Under 800 nm Excitation. J. Appl. Phys. 1999, 85, 29−37. (191) Khichar, N.; Bishnoi, S.; Chawla, S. Introducing Dual Excitation and Tunable Dual Emission in ZnO Through Selective Lanthanide (Er3+/Ho3+) Doping. RSC Adv. 2014, 4, 18811−18817. 2636

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637

ACS Photonics

Review

(211) Yao, N.; Huang, J.; Fu, K.; Deng, X.; Ding, M.; Shao, M.; Xu, X. Enhanced light Harvesting of Dye Sensitized Solar Cells With Up/ down Conversion Materials. Electrochim. Acta 2015, 154, 273. (212) de la Mora, M. B.; Amelines-Sarria, O.; Monroy, B. M.; Hernandez-Pérez, C. D.; Lugo, J. E. Materials for Downconversion in Solar Cells: Perspectives and Challenges. Sol. Energy Mater. Sol. Cells 2017, 165, 59−71. (213) Gholizadeh, A.; Reyhani, A.; Parvin, P.; Mortazavi, S. Z. Efficiency Enhancement of ZnO Nanostructure Assisted Si Solar Cell Based on Fill Factor Enlargement and UV-blue Spectral Downshifting. J. Phys. D: Appl. Phys. 2017, 50, 185501. (214) Zhang, Q. F.; Dandeneau, C. S.; Zhou, X. Y.; Cao, G. Z. ZnO Nanostructures for Dye-sensitized Solar Cells. Adv. Mater. 2009, 21, 4087−4108. (215) Xie, R. J.; Hirosaki, N. Silicon Based Oxynitride and Nitride Phosphors for White LEDs-A review. Sci. Technol. Adv. Mater. 2007, 8, 588−600. (216) Fasol, G.; Nakamura, S. The Blue Laser Diode: GaN Based Blue Light Emitters and Lasers; Springer: Berlin, 1997. (217) Steigerwald, D. A.; Bhat, J. C.; Collins, D.; Fletcher, R. M.; Holcomb, M. O.; Ludowise, M. J.; Martin, P. S.; Rudaz, S. L. Illumination With Solid State Lighting Technology. IEEE J. Sel. Top. Quantum Electron. 2002, 8, 310−320. (218) Sheu, J. K.; Chang, S. J.; Kuo, C. H.; Su, Y. K.; Wu, L. W.; Lin, Y. C.; Lai, W. C.; Tsai, J. M.; Chi, G. C.; Wu, R. K. White Light Emission from Near UV InGaN-GaN LED Chip Precoated with Bluegreen-red Phosphors. IEEE Photonics Technol. Lett. 2003, 15, 18−20. (219) Krames, M. R.; Shchekin, O. B.; Mueller-Mach, R.; Mueller, G. O.; Zhou, L.; Harbers, G.; Craford, M. G. Status and Future of High Power Light Emitting Diodes for Solid State Lighting. J. Disp. Technol. 2007, 3, 160. (220) Kim, J. S.; Jeon, P. E.; Choi, J. C.; Park, H. L.; Mho, S. I.; Kim, G. C. Warm White Light Emitting Diode Utilizing a Single Phase Full Color Ba3MgSi2O8:Eu2+,Ba3+ Phosphor. Appl. Phys. Lett. 2004, 84, 2931. (221) Ji, S.; Yin, L.; Liu, G.; Zhang, L.; Ye, C. A Facile Method for Effective Doping of Tb3+ into ZnO Nanocrystals. Chem. Commun. 2009, 7, 2344−2346. (222) Ji, S.; Yin, L.; Liu, G.; Zhang, L.; Ye, C. Synthesis of Rare Earth Ions Doped ZnO Nanostructures with Efficient Host Guest Energy Transfer. J. Phys. Chem. C 2009, 113, 16439−16444. (223) Balestrieri, M.; Gallart, M.; Ziegler, M.; Bazylewski, P.; Ferblantier, G.; Schmerber, G.; Chang, G. S.; Gilliot, P.; Muller, D.; Slaoui, A.; Colis, S.; Dinia, A. Luminescent Properties and Energy Transfer in Pr3+ Doped and Pr3+-Yb3+ Co-doped ZnO Thin Films. J. Phys. Chem. C 2014, 118 (25), 13775−13780. (224) Sun, L. W.; Shi, H. Q.; Li, W. N.; Xiao, H. M.; Fu, S. Y.; Cao, X. Z.; Li, Z. X. Lanthanum Doped ZnO Quantum Dots With Greatly Enhanced Fluorescent Quantum Yield. J. Mater. Chem. 2012, 22, 8221−8227. (225) Foreman, J. V.; Everitt, H. O.; et al. Influence of Temperature and Photoexcitation Density on the Quantum Efficiency of Defect Emission in ZnO Powders. Appl. Phys. Lett. 2007, 91, 011902. (226) Elleuch, R.; Salhi, R.; Al-Quraishi, S. I.; Deschanvres, J. L.; Maalej, R. Efficient Antireflective Downconversion Er3+ Doped ZnO/ Si Thin Film. Phys. Lett. A 2014, 378, 1733−1738. (227) Yang, Y.; Li, Y.; Wang, C.; Zhu, C.; Lv, C.; Ma, X.; Yang, D. Rare Earth Doped ZnO Films: A Material Platform to Realize Multicolor and Near-infrared Electroluminescence. Adv. Opt. Mater. 2014, 2, 240−244. (228) Harako, S.; Yokoyama, S.; Ide, K.; Zhao, X.; Komoro, S. Visible and Infrared Electroluminescence from an Er Doped n-ZnO/p-Si Light Emitting Diode. Phys. Status Solidi A 2008, 205 (1), 19−22. (229) Francesco Pecora, E.; Murphy, T. I.; Dal Negro, L. Rare Earth Doped Si-rich ZnO for Multiband Near-infrared Light Emitting Devices. Appl. Phys. Lett. 2012, 101, 191115. (230) Yang, Y.; Li, Y. P.; Xiang, L. L.; Ma, X. Y.; Yang, D. R. Lowvoltage Driven ∼ 1.54 μm Electroluminescence from Erbium-doped

ZnO/p+-Si Heterostructured Devices: Energy Transfer from ZnO Host to Erbium Ions. Appl. Phys. Lett. 2013, 102, 181111. (231) Swart, H. C. Surface Sensitive Techniques for Advanced Characterization of Luminescent Materials. Materials 2017, 10 (8), 906.

2637

DOI: 10.1021/acsphotonics.7b00777 ACS Photonics 2017, 4, 2613−2637