Size-Dependent Color Tuning of Efficiently Luminescent Germanium

Oct 11, 2012 - International Center for Materials Nanoarchitectonics (WPI-MANA), 1-1 ... (AIST), 2266-98 Anagahora, Shimoshidami, Moriyama, Nagoya...
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Size-Dependent Color Tuning of Efficiently Luminescent Germanium Nanoparticles Naoto Shirahata,*,†,‡,§ Daigo Hirakawa,‡,∥ Yoshitake Masuda,⊥ and Yoshio Sakka‡,∥ †

International Center for Materials Nanoarchitectonics (WPI-MANA), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan § Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan ∥ Graduate School of Pure and Science and Applied Science, The University of Tsukuba, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan ⊥ National Institute of Advanced Industrial Science and Technology (AIST), 2266-98 Anagahora, Shimoshidami, Moriyama, Nagoya 463-8560, Japan ‡

S Supporting Information *

ABSTRACT: It is revealed that rigorous control of the size and surface of germanium nanoparticles allows fine color tuning of efficient fluorescence emission in the visible region. The spectral line widths of each emission were very narrow ( 5 ns) components becomes measurable. Such slow relaxation would be explained by the trapped carrier recombination in the ground state, leading to the appearance of long time-resolved emission tails (Figure S3, Supporting Information). Interestingly, relatively higher visible PL QYs have always been observed from the partially oxidized Ge nanoparticles unlike nonoxidized ones, suggesting a significant role of interfacially related e−h recombination for efficient visible light emission.

Table 2. Room-Temperature PL Properties of Five Different Ge Nanoparticle Fractionsa lifetime, τ(ns) sample

PL QY, ϕ(%)

PL fwhm (meV)

τ1B1 (%)

τ2B2(%)

χ2

0.86 68 0.92 85 1.52 82 1.51 79 2.06 64

3.10 32 2.10 85 5.18 18 6.72 21 8.69 36

1.37

near-UV PL

8

480

violet PL

9

170

blue PL

15

450

light-blue PL

12

500

4

420

green PL a

1.02 1.06 1.05 1.57

The estimates contain a maximum uncertainty of 0.2%.

the PL QYs of Ge nanoparticles. The best PL QY performance reported to date is in the blue spectral regions, ϕ = 11%.8 Other reported values tend to be in the range of ϕ ≤ 1%, which does not satisfy the requirements (ϕ > 1%) even for fluorescence applications such as package tagging and biomedical imaging. Significantly, our luminescent Ge nanoparticles show sufficiently high PL QYs (ϕ = 4%−15%) to qualify for labeling use. The poor optical performance of Ge as a light emitter, as reported in earlier studies, can be explained by time-resolved PL spectroscopy. PL intensity I(t) can be expressed as a function of time



CONCLUSIONS We report here the superior light-emission properties of Ge nanoparticles. Bulk crystalline Ge shows poorer optical performance, and its indirect band gap character is believed to be inherited even in its nanostructures, resulting in emission spectrum broadness and low PL QYs. In the present study, we found that such a broad emission spectrum can be separated into narrow spectral lines by taking advantage of the small difference in surface polarity between nanoparticles and subsequent size purification. In addition to narrower fluorescence spectra, the nanoparticles obtained by emissioncolor separation emit efficiently in the near-UV, violet, blue, light-blue, and green spectral regions. The violet-light-emitting nanoparticle is a new family of luminescent Ge.

I(t ) = B1e−t / τ1 + B2 e−t / τ2

where B and τ are constants determined by curve-fitting decay profiles and are listed in Table 2. The estimated lifetime is expressed as the sum of lifetimes for radiative recombination (τr) and nonradiative recombination (τnr). Because the inverse lifetime is expressed as the recombination probability per unit time, the lifetime determined by both carrier transition processes is expressed as 1/τt = 1/τr + 1/τnr. Thus, PL QY is described by the equation ϕ = 1/(1 + (τr/τnr)). In general, the inefficient recombination process of photogenerated carriers is observed from bulk Ge. However, our Ge nanoparticles efficiently emit light in the visible region. Our findings reported herein reaffirm the significance of nanoparticle size as the prime structural parameter for tuning the light-emission wavelength. In fact, tuning requires control of the both particle size and the particle-size distribution, to a far greater extent than we had predicted. In comparing the optical absorbance and emission spectra in Figure 8, we notice that an additional structural parameter (i.e., surface configuration) is also important to performing color tuning of the emission with a high PL QY. Our obtained PLE spectra can be categorized by spectral shape into two groups: one that includes near-UV and violet luminescent fractions and one that includes all other luminescent fractions. In the spectra of the first group (nearUV and violet luminescent fractions), we see the PLE maxima at photon energies corresponding to structural features that appear as shoulders in the absorption spectra. In addition, PL relaxation processes are essentially dominated by fast components with lifetimes of τ < 1 ns. These emission features are very similar to the properties observed from the nonoxidized Si nanoparticles in which photogenerated carriers are confined for the appearance of the quantum size effect.32,35 In contrast, all of the spectra of the second group (all other



ASSOCIATED CONTENT

S Supporting Information *

1

H NMR spectra of the 1-octene-treated Ge nanoparticle sample and 1-octene and summary of the emission spectral line widths of Ge nanoparticles reported elsewhere when compared to our data. This material is available free of charge via the Internet at http://pubs.acs.org.



AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

N.S. designed the experiment, carried out research, analyzed data, and wrote the article. D.H. carried out research. Y.M. helped to characterize the nanoparticles. Y.S. was involved in the experiment design. All authors discussed the results and commented on the article. Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS We thank the Nanotechnology Innovation Center for the use of its facilities. This work was financially supported by JSTPRESTO, JST A-step (no. AS221Z00791C), a grant-in-aid for challenging exploratory research (no. 23655138), MEXT, and H

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288. (f) He, Y.; Su, Y.; Yang, X.; Kang, Z.; Xu, T.; Zhang, R.; Fan, C.; Lee, S.-T. Photo and pH Stable, Highly-Luminescent Silicon Nanospheres and Their Bioconjugates for Immunofluorescent Cell Imaging. J. Am. Chem. Soc. 2009, 131, 4434−4438. (g) Aptekar, J. W.; Cassidy, M. C.; Johnson, A. C.; Barton, R. A.; Lee, M.; Ogier, A. C.; Vo, C.; Anahtar, M. N.; Ren, Y.; Bhatia, S. N.; Ramanathan, C.; Cory, D. G.; Hill, A. L.; Mair, R. W.; Rosen, M. S.; Walsworth, R. L.; Marcus, C. M. Silicon Nanoparticles as Hyperpolarized Magnetic Resonance Imaging Agents. ACS Nano 2009, 3, 4003−4008. (h) Choi, J.; Wang, N. S.; Reipa, V. Conjugation of the Photoluminescent Silicon Nanoparticles to Streptavidin. Bioconjugate Chem. 2008, 19, 680−685. (4) Maeda, Y.; Tsukamoto, N.; Yazawa, Y.; Kanemitsu, Y.; Masumoto, Y. Visible Photoluminescence of Ge Microcrystals Embedded in SiO2 Glassy Matrices. Appl. Phys. Lett. 1991, 59, 3168. (5) Lee, D. C.; Pietryga, J. M.; Robel, I.; Werder, D. J.; Schaller, R. D.; Klimov, V. I. Colloidal Synthesis of Infrared-Emitting Germanium Nanocrystals. J. Am. Chem. Soc. 2009, 131, 3436−3437. (6) Ruddy, D. A.; Johnson, J. C.; Smith, E. R.; Neale, N. R. Size and Bandgap Control in the Solution-Phase Synthesis of Near-InfraredEmitting Germanium Nanocrystals. ACS Nano 2010, 4, 7459−7466. (7) Wilcoxon, J. P.; Provencio, P. P.; Samara, G. A. Synthesis and Optical Properties of Colloidal Germanium Nanocrystals. Phys. Rev. B 2001, 64, 035417. (8) Prabakar, S.; Shiohara, A.; Hanada, S.; Fujioka, K.; Yamamoto, K.; Tilley, R. D. Size Controlled Synthesis of Germanium Nanocrystals by Hydride Reducing Agents and Their Biological Applications. Chem. Mater. 2010, 22, 482−486. (9) Warner, J. H.; Tilley, R. D. Synthesis of Water-Soluble Photoluminescent Germanium Nanocrystals. Nanotechnology 2006, 17, 3745−3749. (10) Zaitseva, N.; Dai, Z. R.; Grant, C. D.; Harper, J.; Saw, C. Germanium Nanocrystals Synthesized in High-Boiling-Point Organic Solvents. Chem. Mater. 2007, 19, 5174−5178. (11) Lu, X.; Ziegler, K. J.; Ghezelbash, A.; Johnston, K. P.; Korgel, B. A. Synthesis of Germanium Nanocrystals in High Temperature Supercritical Fluid Solvents. Nano Lett. 2004, 4, 969−974. (12) Taylor, B. R.; Kauzlarich, S. M.; Lee, H. W.; Delgado, G. R. Solution Synthesis of Germanium Nanocrystals Demonstrating Quantum Confinement. Chem. Mater. 1998, 10, 22−24. (13) Fok, E.; Shih, M.; Meldrum, A.; Veinot, J. G. C. Preparation of Alkyl-Surface Functionalized Germanium Quantum Dots via Thermally Initiated Hydrogermylation. Chem. Commun. 2004, 386−387. (14) Simple size-selective precipitation: (a) Mastronardi, M. L.; Maier-Flaig, F.; Faulkner, D.; Henderson, E. J.; Kübel, C.; Lemmer, U.; Ozin, G. A. Size-Dependent Absolute Quantum Yields for SizeSeparated Colloidally-Stable Silicon Nanocrystals. Nano Lett. 2012, 12, 337−342. (b) Liu, S.-M.; Yang, Y.; Sato, S.; Kimura, K. Enhanced Photoluminescence from Si Nano-organosols by Functionalization with Alkenes and Their Size Evolution. Chem. Mater. 2006, 18, 637642. (c) Li, X.; He, Y.; Swihart, M. T. Surface Functionalization of Silicon Nanoparticles Produced by Laser-Driven Pyrolysis of Silane Followed by HF−HNO3 Etching. Langmuir 2004, 20, 4720−4727. (15) Density gradient ultracentrifugation (DGU) methods: (a) Mastronardi, M. L.; Hennrich, F.; Henderson, E. J.; Maier-Flaig, F.; Blum, C.; Reichenbach, J.; Lemmer, U.; Kübel, C.; Wang, D.; Kappes, M. M.; Ozin, G. A. Preparation of Monodisperse Silicon Nanocrystals Using Density Gradient Ultracentrifugation. J. Am. Chem. Soc. 2011, 133, 11928−11931. (b) Miller, J. B.; Van Sickle, A. R.; Anthony, R. J.; Kroll, D. M.; Kortshagen, U. R.; Hobbie, E. K. Ensemble Brightening and Enhanced Quantum Yield in Size-Purified Silicon Nanocrystals. ACS Nano 2012, 6, 7389−7396. (16) Shirahata, N.; Hirakawa, D.; Sakka, Y. Interfacial-Related Color Tuning of Colloidal Si Nanocrystals. Green Chem. 2010, 12, 2139− 2141. (17) Shirahata, N.; Linford, M. R.; Furumi, S.; Pei, L.; Sakka, Y.; Gates, R. J.; Asplund, M. C. Laser-Derived One-Pot Synthesis of Silicon Nanocrystals Terminated with Organic Monolayers. Chem. Commun. 2009, 4684.

the Konica Minolta Imaging Science Award from the Konica Minolta Science and Technology Foundation, Japan.

■ ■

ABBREVIATION TLC, thin layer chromatography REFERENCES

(1) Recent reviews of solution-processed group IV nanoparticles: (a) Shirahata, N. Colloidal Si Nanocrystals: A Controlled OrganicInorganic Interface and Its Implications of Color-Tuning and Chemical Design toward Sophisticated Architectures. Phys. Chem. Chem. Phys. 2011, 13, 7284−7294. (b) Fan, J.; Chu, P. K. Group IV Nanoparticles: Synthesis, Properties, and Biological Applications. Small 2010, 6, 2080−2098. (c) Veinot, J. G. C. Synthesis, Surface Functionalization, and Properties of Freestanding Silicon Nanocrystals. Chem. Commun. 2006, 4160−4168. (2) Examples of nanocrystalline silicon-based optoelectonic devices: (a) Mastronardi, M. L.; Henderson, E. J.; Puzzo, D. P.; Chang, Y.; Wang, Z. B.; Helander, M. G.; Jeong, J.; Kherani, N. P.; Lu, Z.; Ozin, G. A. Silicon Nanocrystal OLEDs: Effect of Organic Capping Group on Performance. Small 2012, in press. (b) Regli, S.; Kelly, J. A.; Shukaliak, A. M.; Veinot, J. G. C. Photothermal Response of Photoluminescent Silicon Nanocrystals. J. Phys. Chem. Lett. 2012, 3, 1793−1797. (c) Tétreault, N.; Arsenault, E.; Heiniger, L.-P.; Soheilnia, N.; Brillet, J.; Moehl, T.; Zakeeruddin, S.; Ozin, G. A.; Grätzel, M. Visible Colloidal Nanocrystal Silicon Light-Emitting Diode. Nano Lett. 2011, 11, 1585−1590. (d) Cheng, K. Y.; Anthony, R.; Kortshagen, U. R.; Holmes, R. J. High-Efficiency Silicon Nanocrystal Light-Emitting Devices. Nano Lett. 2011, 11, 1952−1956. (e) Pereira, R. N.; Niesar, S.; You, W. B.; da Cunha, A. F.; Erhard, N.; Stegner, A. R.; Wiggers, H.; Willinger, M.-G.; Stutzmann, M.; Brandt, M. S. Solution-Processed Networks of Silicon Nanocrystals: The Role of Internanocrystal Medium on Semiconducting Behavior. J. Phys. Chem. C 2011, 115, 20120−20127. (f) Katsaros, G.; Spathis, P.; Stoffel, M.; Fournel, F.; Mongillo, M.; Bouchiat, V.; Lefloch, F.; Rastelli, A.; Schmidt, O. G.; De Franceschi, S. Hybrid Superconductor−Semiconductor Devices made from Self-Assembled SiGe Nanocrystals on Silicon. Nat. Nanotechnol. 2010, 5, 458−464. (g) Kim, H.; Kim, B. K.; Kim, W.; Ko, H.; Choi, C. J.; Sung, G. Y. Enhancement in Light Emission Efficiency of a Silicon Nanocrystal Light-Emitting Diode by MultipleLuminescent Structures. Adv. Mater. 2010, 22, 5058−5062. (h) Cheng, K. Y.; Anthony, R.; Kortshagen, U. R.; Holmes, R. J. Hybrid Silicon Nanocrystal−Organic Light-Emitting Devices for Infrared Electroluminescence. Nano Lett. 2010, 10, 1154−1157. (i) Sun, B.; Findikoglu, A. T.; Sykora, M.; Werder, D. J.; Klimov, V. I. Hybrid Photovoltaics Based on Semiconductor Nanocrystals and Amorphous Silicon. Nano Lett. 2009, 9, 1235−1241. (j) Kim, S. K.; Kim, B. H.; Cho, C. H.; Park, S. J. Size-Dependent Photocurrent of Photodetectors with Silicon Nanocrystals. Appl. Phys. Lett. 2009, 94, 183106. (3) Examples of silicon nanocrystals for bioimaging: (a) Singh, M. P.; Atkins, T. M.; Muthuswamy, E.; Kamali, S.; Tu, C.; Louie, A. Y.; Kauzlarich, S. M. Development of Iron-Doped Silicon Nanoparticles As Bimodal Imaging Agents. ACS Nano 2012, 6, 5596−5604. (b) Manhat, B. A.; Brown, A. L.; Black, L. A.; Ross, J. B. A.; Fichter, K.; Vu, T.; Richman, E.; Goforth, A. M. One-Step Melt Synthesis of Water-Soluble, Photoluminescent, Surface-Oxidized Silicon Nanoparticles for Cellular Imaging Applications. Chem. Mater. 2011, 23, 2407−2418. (c) Erogbogbo, F.; Yong, K.-T.; Roy, I.; Hu, R.; Law, W.C.; Zhao, W.; Ding, H.; Wu, F.; Kumar, R.; Swihart, M. T.; Prasad, P. N. In Vivo Targeted Cancer Imaging, Sentinel Lymph Node Mapping and Multi-Channel Imaging with Biocompatible Silicon Nanocrystals. ACS Nano 2011, 5, 413−423. (d) Henderson, E. J.; Shuhendler, A. J.; Prasad, P.; Baumann, V.; Maier-Flaig, F.; Faulkner, D. O.; Lemmer, U.; Wu, X. U.; Ozin, G. A. Colloidally Stable Silicon Nanocrystals with Near-Infrared Photoluminescence for Biological Fluorescence Imaging. Small 2011, 7, 2507−2516. (e) Tu, C.; Ma, X.; House, A.; Kauzlarich, S. M.; Louie, A. Y. PET Imaging and Biodistribution of Silicon Quantum Dots in Mice. ACS Med. Chem. Lett. 2011, 2, 285− I

dx.doi.org/10.1021/la303482s | Langmuir XXXX, XXX, XXX−XXX

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Article

(33) Examples of theoretical study on L-to-X crossing for Ge and Si nanoparticles: (a) Reboredo, F. A.; Zunger, A. L-to-X Crossover in the Conduction-Band Minimum of Ge Quantum Dots. Phys. Rev. B 2000, 62, 2275−2278. (b) Takagahara, T.; Takeda, K. Excitonic Exchange Splitting and Stokes Shift in Si Nanocrystals and Si Clusters. Phys. Rev. B 1996, 53, 4205−4208. (34) English, D. S.; Pell, L. E.; Yu, Z.; Barbara, P. F.; Korgel, B. A. Size Tunable Visible Luminescence from Individual Organic Monolayer Stabilized Silicon Nanocrystal Quantum Dots. Nano Lett. 2002, 2, 681−685. (35) Shirahata, N.; Sakka, Y. Controlled Organic/Inorganic Interface Leading to the Size-Tunable Luminescence from Si Nanoparticles. J. Ceram. Soc. Jpn. 2010, 118, 932−939.

(18) Shirahata, N.; Yonezawa, T.; Seo, W. S.; Koumoto, K. Photoinduced Cleavage of Alkyl Monolayers on Si. Langmuir 2004, 20, 1517−1520. (19) Holman, Z. C.; Kortshagen, U. R. Solution-Processed Germanium Nanocrystal Thin Films as Materials for Low-Cost Optical and Electronic Devices. Langmuir 2009, 25, 11883−11889. (20) Henderson, E. J.; Hessel, C. M.; Veinot, J. C. G. Synthesis and Photoluminescent Properties of Size-Controlled Germanium Nanocrystals from Phenyl Trichlorogermane-Derived Polymers. J. Am. Chem. Soc. 2008, 130, 3624−3632. (21) FTIR spectrum of oxidized Ge: (a) Ardyanian, M.; Rinnert, H.; Vergnat, M. Influence of Hydrogenation on the Structure and Visible Photoluminescence of Germanium Oxide Thin Films. J. Lumin. 2009, 129, 729−733. (b) Gerung, H.; Bunge, S. D.; Boyle, T. J.; Brinker, C. J.; Han, S. M. Anhydrous Solution Synthesis of Germanium Nanocrystals from the Germanium(II) Precursor Ge[N(SiMe3)2]2. Chem. Commun. 2005, 1914−1916. (22) Henderson, E. J.; Seino, M.; Puzzo, D. P.; Ozin, G. A. Colloidally Stable Germanium Nanocrystals for Photonic Applications. ACS Nano 2010, 4, 7683−7691. (23) Cambell, I. H.; Fauchet, P. M. The Effects of Microcrystal Size and Shape on the One Phonon Raman Spectra of Crystalline Semiconductors. Solid State Commun. 1986, 58, 739−741. (24) Hellwege, K. H. Landolt-Bornstein Numerical Data and Functional Relationships in Science and Technology; Springer-Verlag: Berlin, 1982; Vol. 17, p 115. (25) Yang, H.; Yao, X.; Wang, X.; Xie, S.; Fang, Y.; Liu, S.; Gu, X. Sol−Gel Preparation and Photoluminescence of Size Controlled Germanium Nanoparticles Embedded in a SiO2 Matrix. J. Phys. Chem. B 2003, 107, 13319−13322. (26) Kartopu, G.; Bayliss, S. C.; Hummel, R. E.; Ekinci, Y. Simultaneous Micro-Raman and Photoluminescence Study of SparkProcessed Germanium: Report on the Origin of the Orange Photoluminescence Emission Band. J. Appl. Phys. 2004, 95, 3466− 3472. (27) Examples of Raman spectra attributed to amorphous Ge: (a) Bara, Y.; Kabiraj, D.; Kanjilal, D. Charge Retention and Optical Properties of Ge Nanocrystals Embedded in GeO2 Matrix. Solid State Commun. 2007, 143, 213−216. (b) Kartopu, G.; Karavanskii, V. A.; Serincan, U.; Turan, R.; Hummel, R. E.; Ekinci, Y.; Gunnæs, A.; Finstad, T. G. Can Chemically Etched Germanium or Germanium Nanocrystals Emit Visible Photoluminescence? Phys. Status Solidi 2005, 202, 1472−1476. (28) Kartopu, G.; Bayliss, S. C.; Karavanski, V. A.; Curry, R. J.; Turan, R.; Sapelkin, A. V. On the Origin of the 2.2−2.3 eV Photoluminescence from Chemically Etched Germanium. J. Lumin. 2003, 101, 275−283. (29) Lu, X.; Korgel, B. A.; Johnston, K. P. High Yield of Germanium Nanocrystals Synthesized from Germanium Diiodide in Solution. Chem. Mater. 2005, 17, 6479−6485. (30) Shirahata, N.; Hozumi, A.; Yonezawa, T. Monolayer-Derivative Functionalization of Non-Oxidized Silicon Surfaces. Chem. Rec. 2005, 5, 145−159. (31) Typical optical absorption spectra of collidal Ge nanopaticles: (a) Taylor, B. R.; Kauzlarich, S. M. Solution Synthesis and Characterization of Quantum Confined Ge Nanoparticles. Chem. Mater. 1999, 11, 2493−2500. (b) Kornowski, A.; Giersig, M.; Vogel, R.; Chemseddine, A.; Weller, H. Nanometer-Sized Colloidal Germanium Particles: Wet-Chemical Synthesis, Laser-Induced Crystallization and Particle Growth. Adv. Mater. 1993, 5, 634−636. (c) Sato, S.; Ikeda, T.; Hamada, K.; Kimura, K. Size Regulation by Bandgap-Controlled Etching: Application to Germanium Nanoparticles. Solid State Commun. 2009, 149, 862−865. (32) Typical UV−vis spectra of colloidal Si nanoparticles: (a) Shirahata, N.; Tsuruoka, T.; Hasegawa, T.; Sakka, Y. Size-Tunable UV-Luminescent Silicon Nanocrystals. Small 2010, 6, 915−921. (b) Rosso-Vasic, M.; Spruijt, E.; van Lagen, B.; De Cola, L.; Zuilhof, H. Alkyl-Functionalized Oxide-Free Silicon Nanoparticles: Synthesis and Optical Properties. Small 2008, 4, 1835−1841. J

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