Photoluminescence and Two-Photon Lasing of ZnO:Sn Microdisks

Subscriber access provided by UNIV NEW ORLEANS

Article

Photoluminescence and Two-photon Lasing of ZnO:Sn Microdisks Jun Dai, Chunxiang Xu, Jitao Li, Yi Lin, JiYuan Guo, and Gangyi Zhu J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 12 Jun 2014 Downloaded from http://pubs.acs.org on June 15, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Photoluminescence and Two-photon Lasing of ZnO:Sn Microdisks Jun Dai, 1,2, a) Chunxiang Xu,2,a*) Jitao Li,2 Yi Lin,2 Jiyuan Guo,1,2 Gangyi Zhu2 1

School of Mathematics and Physics, Jiangsu University of Science and Technology, Zhenjiang 212003, China State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China 2

Abstract: ZnO:Sn microdisks were fabricated by a vapor phase transport method at different pressure conditions. The photoluminescence of the ZnO:Sn microdisks was measured, and the origination of defect emission was attributed to the oxygen vacancy defects. Under the excitation of 532 nm line of a femtosecond pulsed laser, two-photon absorption induced UV amplified spontaneous emission and whispering-gallery mode lasing were observed from the ZnO:Sn microdisks. The electron-hole plasma induced red-shift and broadening of the amplified spontaneous emission and lasing emission were demonstrated when the excitation power was increased. In addition, the WGM lasing light distribution was simulated by a numerical method.

Keywords: ZnO, microdisk, two-photon, optical cavity, lasing, electron-hole plasma

PACS number: 78.45.+h, 42.55.Sa

a)

Correspondence authors: E-mail: [email protected] (J. Dai); [email protected] (C. X. Xu)

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 20

1. INTRODUCTION

Low dimensional semiconductor materials have drawn much attention due to their unique properties and potential applications in optoelectronics devices.1,2 As a wide band gap (3.37 eV) semiconductor material, ZnO is considered as a promising ultraviolet laser material because of its large exciton binding energy (60 meV).3-6 Optically pumped random lasing in ZnO was firstly reported in 1997,6 and then Fabry-Perot lasing from ZnO nanowires and nanorods were observed by different groups.5,7,8 ZnO is also a kind of nonlinear optical material, strong multi-photon absorption (MPA) of ZnO has promising applications in frequency converters and MPA lasers.9,10 Recently a new kind of lasing mechanism, whispering gallery mode (WGM) lasing, attracts researchers’ interests for its high quality factor and low lasing threshold.11-15 Two-photon and multi-photon induced WGM lasing actions

have

been

observed

in

the

ZnO

hexagonal

microrods/wires.16,17

ZnO

micro/nanostructures generally present one-dimensional wire/rod structure for its preferential growth along direction. However, it is still a challenge to fabricate two-dimensional disk-shaped ZnO microcavities which are more compatible in the optoelectronic devices. Therefore, it is of importance to design a method to fabricate the two-dimensional diskshaped ZnO microstructures. Xu et al. firstly reported that perfect hexagonal ZnO microdisks could be fabricated by vapor phase transport method (VPT) using ZnO, In2O3 and graphite as source materials.18 Then whispering gallery mode frequency converter was observed from the ZnO microdisks by Zhang et al.17 However, it is very difficult to repeat the growth of the perfect ZnO microdisk. Recently researchers found that plate-like ZnO:Sn microstructure can also be obtained using ZnO, SnO2 and graphite as source materials.19, 20 So metal doping (In, Sn) is a desirable method to obtain the plate-shape ZnO material, because the metal (In, Sn) doping can change the surface energy and suppress the the growh along direction.18 It


Page 3 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is worth noticing that Sn is a cheap and widely existing metal, and Sn doped ZnO can increase the carrier density, such property is helpful to realize high efficiency optoelectronics device. In addition, SnO2 has a band gap (3.62 eV), ZnO:Sn with very low Sn-doping content still can have a direct band gap very close to that of the pure ZnO. As a result, it is desirable to obtain 2-dimensional disk-shape ZnO:Sn microstructure which can be applied in the field of

2-dimensional

ultraviolet

whispering-gallery

mode

microlaser.

Although

the

photoluminescence mechanism (exciton and defect emission), lasing and two-photon phenomena have been deeply investigated in ZnO microstructure, the optical properties (defect emission, two-photon lasing and so on) from the disk-shaped ZnO:Sn microstructures have not been discussed.

In this paper, ZnO:Sn microdisks were synthesized by a vapor phase transport method at different pressure conditions. The photoluminescence from the ZnO:Sn microstructures was measured and discussed. Further, the two-photon absorption induced UV electron-hole plasma amplified spontaneous emission (ASE) and WGM lasing were obtained from the ZnO:Sn microdisks under the excitation of 532 nm line of a femtosecond laser.

2. EXPERIMENTAL METHODS

ZnO:Sn microdisks were synthesized by a typical vapor transport method. The sapphire substrates (3 cm×0.5 cm) were ultrasonically cleaned in acetone, ethanol and deionized water for 5 minutes successively. 0.25 g ZnO powder, 0.0463g SnO2 powder and 0.25 g graphite were mixed and filled in a ceramic boat. The ceramic boat filled with source material was placed in a tube (length: 30 cm, diameter: 3 cm). A piece of sapphire substrate was placed 5 cm downstream away from the ceramic boat. The tube loaded with the ceramic boat and the sapphire substrate was then pushed into a horizontal furnace, the temperature at the ceramic boat was 1000 °C, the temperature at the substrate position was about 800 °C. In



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the reaction process, oxygen and argon gases were loaded in the horizontal furnace with the flow rates of 15 sccm and 150 sccm, respectively. Three samples were fabricated after 40 minutes at different reaction pressures (1 Torr, 20 Torr and 1 atm). The surface morphology was studied by a Zeiss SEM. X-ray diffraction was measured by XRD-6000X. X-ray photoelectron spectrum was tested by Axis Ultra. Photoluminescence (PL) was measured by a Fluorescence spectrophotometer F-4600 (Hitachi). Two-photon amplified spontaneous emission (ASE) and WGM lasing were measured by a micro-photoluminescence system (Olympus), and the optical spectra were collected by a spectrometer (SpectraPro-2500i, Acton Research Corporation). The light distribution pattern from the hexagonal microdisk was simulated by a numerical FDTD method.

3. RESULTS AND DISCUSSIONS

Figure 1 shows the SEM images of the ZnO:Sn microdisks which were synthesized at 1 Torr, 20 Torr and 1 atm, respectively. As shown in Figure 1a, the surface of the sample I grown at 1 Torr presents densely stacked disks with irregular boundary, and these disks almost lay on the substrate. For the sample II grown at 20 Torr, the stacked disks [Figure 1b] have larger size, and some of the disks have corner angle of 120 degrees, which looks like the corner of the hexagonal ZnO microstructure. The sample III grown at 1 atm [Figure 1c] shows regular hexagonal microdisk structure. The regular hexagonal ZnO:Sn microdisks were then dispersed on a silicon substrate for optical experiment. Figure 1d shows the SEM image of a hexagonal ZnO:Sn microdisk dispersed on the silicon substrate, its diameter is 2.52 µm. The growth mechanism of the disk shape is related to the Sn doping effect. The Sn doped ZnO will increase the surface energy of (0001), which can suppress the growth along the direction of [001] and result in a faster growth of ZnO:Sn crystal along to form the hexagonal disk structure.[19] Figure 2 shows the XRD patterns of the three sample. The XRD pattern for


Page 4 of 20

Page 5 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the sample I grown at 1 Torr only has a sharp diffraction peak at 34.3° and a weak peak at 63.2°, which are indexed to the diffraction peaks from (002) and (103) surfaces, respectively. For the sample II and III grown at 20 Torr and 1 atm, six peaks at 31.5°, 34.2°, 36.2°, 47.2°, 56.6° and 62.9° originated from the wurtzite structure of the ZnO:Sn hexagonal disks can be observed, as shown in Figure 2b and 2c. No traces of SnO2 or ZnSnO3 can be found in the XRD pattern. To further confirm the existence of Sn in the microdisks, EDS was used to determine the element composition of the samples. The EDS spectra of the three samples are shown in Figure 3, weak Sn element signal peaks can be found. The inset of Figure 3(a) shows the EDS signal originating from the Sn element of the sample I. According to EDS spectra, the atomic ratio of Sn/(Sn+Zn) of the three samples are 0.5%, 0.9% and 1.5%, respectively. The EDS result indicates that only a small amount of Sn atoms were doped into the ZnO microdisks. The inset of Figure 3c shows the Zn, O and Sn element mapping of a selected rectangular on a microdisk. So the XRD and EDS results indicate that ZnO:Sn microdisks with wurtzite crystal structures are formed.

Figure 4a shows the PL spectra of the three samples. Both of the sample I and II show a near band edge exciton emission band at 390 nm and a green defect emission band at 510 nm. For the sample II, the defect emission has a much stronger relative intensity than that of sample I. For the sample III fabricated at 1 atm, the PL spectrum has a very weak UV emission band at 390 nm and a strong defect emission band at 540 nm. The UV emission bands at 390 nm of the three samples indicate that the band gaps of the ZnO:Sn microdisks are about 3.18 eV at room temperature. The broad defect emission band of the Sample III contains a green emission sub-band P1 (530 nm) and a yellow emission sub-band P2 (590 nm). For the defect emission from the ZnO micro/nanostructure, it is widely accepted the green emission and yellow emission originate from the singly charged oxygen vacancy (VO+) and doubly charged oxygen vacancy (VO2+) trapped in the electron-depletion layer, respectively.21 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

From the PL spectra of these three ZnO:Sn samples, the relative intensity of the green defect emission increases and the green emission wavelength shifts from 510 nm to 530 nm with the reaction pressure, meanwhile a yellow emission band appears for the Sample III. According to the defect emission mechanism of the pure ZnO, we speculate that the oxygen vacancy also plays an important role for the defect emission of the ZnO:Sn samples. The fine XPS spectra of O 1s were measured to analyse the oxygen vacancy defect density in the ZnO:Sn samples. In Figure 4b the fine spectra of the O 1s peaks for the three samples show asymmetric peaks which can be fitted by two Gaussian peaks at 529.9 and 531.0 eV. The XPS peak A at 529.9 eV is mainly attributed to O2- 1s core level of ZnO, and the peak B at 531.0 eV is attributed to oxygen vacancy deficient state.21 Figure 4c shows the XPS intensity ratio (IB/IA) of the peak B to peak A and the PL intensity ratio (Igreen/IUV) of the green defect emission to the UV emission for the three samples. IB/IA and Igreen/IUV have similar change tendency. To some extent, the result indicates that the defect emission is originated from oxygen vacancies. Although the reaction condition for sample III is of more abundant oxygen than that for fabricating sample I and II, the defect emission originated from oxygen vacancies is much stronger. It is the reason that the reduction reaction of ZnO in the air is extremely fast and intensive, high density and pressure Zn vapor was quickly generated and expanded to the low temperature zone, which result in a relative lower oxygen density than the Zn vapor density in the tube, so the oxygen vacancy content is much higher than the sample I and II. When the excitation intensity increases, the electron-depletion layer trapping oxygen vacancy defects becomes thin, and the photoexcited free-carrier concentration increases.22 Therefore, the UV emission will be strengthened and the defect emission will be suppressed under high excitation intensity,22, 23 and even the lasing action can be reached.

To observe two-photon absorption (2PA) induced stimulated emission, the micro-PL technique was employed to excite the ZnO:Sn microdisks by the 532 nm femtosecond laser


Page 6 of 20

Page 7 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


pulses, the excitation spot had a diameter of about 2 µm. For the pure ZnO without defect levels, the 2PA process is as following: an electron in the valence band absorbs two photons and transfers to the conduction band, then recombines with the hole in the valence band to form the UV emission. Here, the oxygen vacancy defect level in ZnO:Sn microdisks maybe provide a real energy level and assist the realization of the two-photon photoluminescence (2PPL). Figure 5(a) shows the 2PPL spectra of Sample I excited by the 532 nm femtosecond laser at different excitation power. When the excitation power was lower than 5 mW, the FWHM of the 2PPL emission band was about 15 nm. When the excitation power was increased to 10 mW, the FWHM of the 2PPL emission was decreased to 3 nm which was much smaller than that of the spontaneous emission shown in Figure 4a. The narrowed emission band indicates that the two-photon amplified spontaneous emission occurred under the intensive excitation. When the excitation power increased from 10 mW to 35 mW, the 2PPL emission band gradually shifted to 400 nm, and the FWHM is increased to about 10 nm. In theory, the emission intensity should quadratically increase with the excitation power for the two-photon process. As shown in the inset of Figure 5a, the 2PPL emission intensity (I) linearly depends on the quadratic of excitation power (P2). The linear relationship I∝P2 indicates that the light emission is two-photon absorption induced photoluminescence. Figure 5b shows the redshift and FWHM of emission band with the increasing excitation power. In the previous report, the ZnO excitonic amplified spontaneous emission band showed a continuous narrowing with the increase of excitation intensity, and the center wavelength of the excitonic amplified spontaneous emission band was not changed.24 Here the FWHM of the emission band decreased firstly and then became broadened, and the center wavelength showed an obvious redshift. Such optical phenomena are originated from electron-hole plasma process. Because the high excitation intensity can make the electron-hole pair of the exciton separate, and when the carrier density reaches the Mott transition, the electron-hole



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

plasma state can be formed.25, 26 The typical characteristics of the electron-hole plasma state is the redshift and broadening of the emission band which have been observed in the ZnO thin film and one-dimensional nanorod.3 Similarly, the sample II presents electron-hole plasma emission spectra. Although the excitation power is very high, no obvious lasing action can be observed from Sample I and II because both of the two samples have no regular optical cavity structures.

A hexagonal ZnO:Sn microdisk with diameter of about 5.2 µm was selected to observe the 2PA lasing. When the excitation power was 5 mW, the 2PPL spectrum from the ZnO:Sn microdisk showed a broad spontaneous emission band at 393 nm with FWHM of about 10 nm. When the excitation power was increased to 10 mW, the FWHM of the emission band decreased to about 5 nm, two clear and sharp emission peaks emerged out at 390.13 nm and 391.88 nm, which indicated that the lasing action was formed. When the excitation power increased to 12 mW, the emission band was obviously broadened, and three other lasing peaks at 394.06, 396.41 and 398.78 nm appeared at the long wavelength side, the average mode spacing for the lasing modes is 2.16 nm, and the FWHM (δλ) for the strongest lasing peak at 394.06 nm is about 0.7 nm, so the lasing quality factor is about 560 according to the equation Q=λ/δλ, where λ and δλ are the peak wavelength and the FWHM. When the excitation power increased from 5 mW to 16 mW, the FWHM of the UV emission band decreased firstly and then increased, meanwhile the UV emission band shifted to the long wavelength side. Such band broadening and redshift are also caused by the electron-hole plasma effect as discussed above. Two kinds of lasing mechanisms maybe attribute to the lasing action in the microdisk. One is the Fabry-Perot mode (Figure 6b) formed between two opposite edges on the hexagonal surface, the mode spacing for the F-P modes is ∆λ=λ2⁄2L(n-

λdn/dλ), n ≈ 2.4 is the refractive index, and λ is the lasing wavelength, dn/dλ = -0.01 nm-1,


Page 8 of 20

Page 9 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


L=4.5 µm is the cavity length which is equal to the distance between the two opposite facets. If the F-P mode is formed between two facets, the mode spacing ∆λ is about 2.6 nm, which is larger than that observed in the experiment. Because the reflectivity on the ZnO/air interface is very low, so the F-P can not be generated for its high optical loss on the interface. The other possible lasing mode is the whispering gallery mode in the hexagonal cavity as shown in Figure 6(c). Using the WGM resonance equation N =

3 3nD 6 − tan −1 n 3n 2 − 4 ,12 the 2λ π

calculated lasing wavelengths agree wells with that shown in the lasing spectrum. So we conclude that the lasing in the microdisk is a whispering gallery mode lasing, and the lasing peaks are indexed from 78 to 81. The good WGM cavity confinement can enhance the nonlinear interaction between the 532 nm excitation light and the ZnO:Sn optical gain medium, so the 2PA WGM lasing can be generated in the hexagonal ZnO:Sn microdisk. The inset shows the relationship between the integrated emission intensity and the excitation power density, which fits well to an S-shape curve described by the Casperson model for multi-mode laser.7 The lasing threshold is estimated as 10 mW. It is noted that the lasing peaks become broadened when the excitation power was increased to 16 mW. The lasing peak broadening is mainly attributed to the homogeneous broadening effect which is caused by the interaction between the photons and the phonons at the high carrier density of EHP lasing condition. In addition, a FDTD numerical method was employed to simulate the 2dimensional optical field distributions of the WGM lasing modes in the microcavity. A Gaussian beam with wavelength of 394.06 nm, which corresponds to a lasing mode in the microdisk, was set as the light source. The refractive index of ZnO microdisk is set as 2.4, and the diameter of the hexagonal microdisk is 5.2 µm. Figure 6(d) shows the light distribution of the whispering gallery mode, the light mainly emits out from the six corners, this results agree well with the previous report by J. Wiersig.27 It is obvious that the Fabry-Perot mode between



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

two opposite facets is not formed in the hexagonal. The FDTD result proves that the lasing action in the microdisk is a WGM lasing.

4. CONCLUSIONS

In summary, the hexagonal ZnO:Sn microdisks were fabricated by a vapour transport method. The XPS result indicated that the defect emission is induced by the oxygen vacancy defects. Under the excitation of femtosecond pulsed laser with a wavelength of 532 nm, the typical EHP process was observed in the 2PA amplified spontaneous emission and WGM lasing. The WGM lasing modes and the light distribution were calculated. The results indicate that ZnO:Sn microdisk can be used as WGM microlaser cavity.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (C. X. Xu), [email protected] (J. Dai) Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by NSFC (11104119, 61275054, 11304128, 61106117), 973 Program (2013CB932903 and 2011CB302004), MOE(20110092130006), JSIS(BE2012164), Open Research Fund of State Key Laboratory of Bioelectronics, China Postdoctoral Science Foundation (2014M551485) and QingLan project of Jiangsu Province.

10 Environment ACS Paragon Plus

Page 10 of 20

Page 11 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES 1.

Pan, Z. W.; Dai, Z. R.; Wang, Z. L. Nanobelts of Semiconducting Oxides. Science 2001, 291, 19471949

2.

Gudiksen, M. S.; Lauhon, L. J.; Wang, J.; Smith, D. C.; Lieber, C. M. Growth of Nanowire Superlattice Structures for Nanoscale Photonics and Electronics. Nature 2002, 415, 617-620

3.

Bagnall, D. M.; Chen, Y. F.; Zhu, Z.; Yao, T.; Koyama, S.; Shen, M. Y.; Goto, T. Optically Pumped Lasing of ZnO at Room Temperature. Appl. Phys. Lett. 1997, 70, 2230-2232

4.

Cao, H.; Zhao, Y. G.; Ho, S. T.; Seelig, E. W.; Wang, Q. H.; Chang, R. P. H. Random Laser Action in Semiconductor Powder. Phys. Rev. Lett. 1999, 82, 2278

5.

Huang, M. H.; Mao, S.; Feick, H.; Yan, H. Q.; Wu, Y. Y.; Kind, H.; Weber, E.; Russo, R.; Yang, P. D. Room-Temperature Ultraviolet Nanowire Nanolasers. Science 2001, 292, 1897

6.

Tang, Z. K.; Wong, G. K. L.; Yu, P.; Kawasaki, M.; Ohtomo, A.; Koinuma, H.; Segawa, Y. RoomTemperature Ultraviolet Laser Emission from Self-Assembled ZnO Microcrystallite Thin Films. Appl. Phys. Lett. 1998, 72, 3270-3272

7.

Zimmler, M. A.; Bao, J.; Capasso, F.; Muller, S.; Ronning, C. Laser Action in Nanowires: Observation of the Transition from Amplified Spontaneous Emission to Laser Oscillation. Appl. Phys. Lett. 2008, 93, 051101

8.

Versteegh, M. M.; Vanmaekelbergh, D.; Dijkhuis, J. I. Phys. Rev. Lett. 2012, 108, 157402

9.

Zhang, C. F.; Dong, Z. W.; You, G. J.; Qian, S. X.; Deng, H.; Gao, H.; Yang, L. P.; Li, Y. Observation of Two-Photon-Induced Photoluminescence in ZnO Microtubes Appl. Phys. Lett. 2005, 87, 051920

10. Zhang, C. F.; Dong, Z. W.; You, G. J.; Zhu, R. Y.; Qian, S. X.; Deng, H.; Cheng, H.; Wang, J. C. Femtosecond Pulse Excited Two-Photon Photoluminescence and Second Harmonic Generation in ZnO Nanowires Appl. Phys. Lett. 2006, 89, 042117 11. Chen, R.; Ling, B.; Sun, X. W.; Sun, H. D. Room Temperature Excitonic Whispering Gallery Mode Lasing from High-Quality Hexagonal ZnO Microdisks Adv. Mater. 2011, 23, 2199 12. Czekalla, C.; Sturm, C.; Schmidt-Grund, R.; Cao, B. Q.; Lorenz, M.; Grundmann, M. Whispering Gallery Mode Lasing in Zinc Oxide Microwires Appl. Phys. Lett. 2008, 92, 241102 13. Czekalla, C.; Sturm, C.; Schmidt-Grund, R.; Cao, B. Q.; Perez, J. Z.; Lorenz, M.; Grundmann, M. Optical Characterization of Zinc Oxide Microlasers and Microwire Core-Shell Heterostructures, Journal of Vacuum Science & Technology B 2009, 27, 1780 14. Wang, D.; Seo, H. W.; Tin, C. C.; Bozack, M. J.; Williams, J. R.; Park, M.; Tzeng, Y. J. Appl. Phys. 2006, 99, 093112 15. Gargas, D. J.; Moore, M. C.; Ni, A.; Chang, S. W.; Zhang, Z. Y.; Chuang, S. L.; Yang, P. D. Whispering Gallery Mode Lasing from Zinc Oxide Hexagonal Nanodisks ACS Nano 2010, 4, 32703276 16. Dai, J.; Xu, C. X.; Sun, X. W. Single-Photon and Three-Photon Absorption Induced WhisperingGallery Mode Lasing in ZnO Micronails. Opt. Commun. 2011, 284, 4018



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

17. Zhang, C. F.; Zhang, F.; Sun, X. W.; Yang, Y.; Wang, J.; Xu, J. Frequency-Upconverted WhisperingGallery-Mode Lasing in ZnO Hexagonal Nanodisks. Opt. Lett. 2009, 34, 3349 18. Xu, C. X.; Sun, X. W.; Dong, Z. L.; Yu, M. B. Zinc Oxide Nanodisk. Appl. Phys. Lett. 2004, 85, 3878-3880 19. Ortega, Y.; Fernandez, P.; Piqueras, J. Growth and Luminescence of Oriented Nanoplate Arrays in Tin Doped ZnO. Nanotechnology 2007, 18, 115606 20. Ortega, Y.; Fernandez, P.; Piqueras, J. Self-assembled Tin-doped ZnO Nanowire and Nanoplate Structures Grown by Thermal Treatment of ZnS Powder. J. Cryst. Growth 2009, 311, 3231-3234 21. Xu, X. Y.; Xu, C. X.; Dai, J.; Hu, J. G.; Li, F. J.; Zhang, S. Size Dependence of Defect-Induced Room Temperature Ferromagnetism in Undoped ZnO Nanoparticles J. Phys. Chem. C 2012, 116, 8813-8818 22. Vanheusden, K.; Warren, W. L.; Seager, C. H.; Tallant, D. R.; Voigt, J. A.; Gnade, B. E. Mechanisms behind green photoluminescence in ZnO phosphor powders. J. Appl. Phys. 1996, 79, 7983 23. Cui, J. B. Defect control and its influence on exciton emission of electrodeposited ZnO nanorods. J. Phys. Chem. C 2008, 112, 10385-10388 24. Zhu, G. P.; Xu, C. X.; Zhu, J.; Li, X.; Zheng, K.; Liu, J. P.; Lu, C. G.; Cui, Y. P. Characteristics of Ultraviolet Amplified Spontaneous Emission from Zinc Oxide Nanowires. Opt. Mater. 2008, 31, 181183 25. Klingshirn, C.; Hauschild, R.; Fallert, J.; Kalt, H. Room-Temperature Stimulated Emission of ZnO: Alternatives to Excitonic Lasing. Phys. Rev. B 2007, 75, 115203 26. Mitsubori, S.; Katayama, I.; Lee, S. H.; Yao, T.; Takeda, J. Ultrafast Lasing Due to Electron-Hole Plasma in ZnO Nano-Multipods. Journal of Physics-Condensed Matter 2009, 21, 064211 27. Wiersig, J. Hexagonal Dielectric Resonators and Microcrystal Lasers. Phys. Rev. A 2003, 67, 023807


Page 12 of 20

Page 13 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure captions Figure 1. (a-c) The SEM images of the ZnO:Sn microdisks samples I, II and III grown at 1 Torr, 20 Torr and 1 atm. (d) SEM image of an individual microdisk with perfect hexagonal cross section.

Figure 2. (a-c) The XRD patterns for sample I, II and III grown at 1 Torr, 20 Torr and 1 atm.

Figure 3. EDS spectra of the three samples. The inset of Figure 3(a) shows the EDS signal peaks of Sn element in the sample I. The inset of Figure 3(c) is the Zn (red), O (blue) and Sn (green) element mapping of a selected rectangular on a microdisk.

Figure 4. (a) Room temperature PL spectra from sample I, II and III. (b) XPS of O 1s peaks of the three samples. (c) The change tendencies of IB/IA and Igreen/IUV for the three samples.

Figure 5. (a) The two-photon amplified spontaneous spectra at different excitation power densities at 532 nm excitation wavelength. The inset shows the dependence of the UV emission intensity on the excitation power. (b) The redshift and FWHM of the two-photon amplified spontaneous emission variation with the excitation power.

Figure 6. (a) The two-photon WGM lasing spectra at different excitation power densities at 532 nm excitation wavelength. The inset shows the dependence of the UV emisssion intensity on the excitation power. (b, c) F-P and WGM optical pathes. (d) Light distribution of the WGM lasing in the disk cavity.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure. 1 (a-c) The SEM images of the ZnO:Sn microdisks samples I, II and III grown at 1 Torr, 20 Torr and 1 atm. (d) SEM image of single microdisk with perfect hexagonal cavity shape.


Page 14 of 20

Page 15 of 20

30

40

50

60

(a)

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(b)

(c) 30

40

50

2θ degree

60

Figure 2 (a-c) The XRD patterns for sample I, II and III grown at 1 Torr, 20 Torr and 1 atm.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. (a-c) EDS survey spectra for the sample I, II and III. The inset of Figure 3(a) shows the EDS signal peaks of Sn element in the sample I. The inset of Figure 3(c) shows a microdisk, and the Zn, O and Sn element mapping of a selected rectangular on the microdisk.


Page 16 of 20

Page 17 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4 (a) Room temperature PL spectra from sample I, II and III. (b) XPS of O 1s peaks of the three samples. (c) The change tendencies of IB/IA and Igreen/IUV for the three samples.



Intensity(a.u.)

2PPL intensity(a.u.)

(a)

5 mW 10 mW 15 mW 20 mW 25 mW 30 mW 35 mW

300 600 900 1200 2

2

P (mW )

385

390

395

400

405

Wavelength(nm)

12

(b) 9

Redshift (nm)

Redshift FWHM

10

6

8 6

3 4 0

FWHM (nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 20

2 5

10

15

20

25

30

35

40

P (mW) Figure 5.(a) The two-photon amplified spontaneous spectra at different excitation power densities at 532 nm excitation wavelength. The inset shows the dependence of the UV emission intensity on the excitation power. (b) The redshift and FWHM of the two-photon amplified spontaneous emission variation with the excitation power.


16 mW

(a)

14 mW

Intensity(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Normalized Intensity (a.u.)

Page 19 of 20

12 mW 10 mW 6 9 12 15 Pumping power (mW)

5 mW 360

370

380

390

400

410

wavelength (nm)

Figure 6. (a) The two-photon WGM lasing spectra at different excitation power densities at 532 nm excitation wavelength. The inset shows the dependence of the FWHM of the UV emission band on the excitation power. (b, c) F-P and WGM optical pathes. (d) Light distribution of the WGM lasing in the disk cavity.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Contents (TOC) Image


Page 20 of 20

Photoluminescence and Two-Photon Lasing of ZnO:Sn Microdisks

Recommend Documents