Open Access
Add to BibSonomy
Abstract
We report the CsPbI3 random lasing at room temperature fabricated by a chemical deposition method. The CsPbI3 thin films with high crystalline quality have intense PL emission and easily achieve the lasing behavior with the Q-factor value over 7000. The lasing behavior of CsPbI3 thin films can be classified as random lasing by measuring lasing spectra at different collective angles. The fast Fourier transform analysis of the lasing spectra is employed to determine the effective cavity length. Most important of all, the lasing stability investigation shows the prolonged lasing stability over 4.8 X 105 laser shots in air.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
2. Introduction
Organic-inorganic hybrid perovskites with the general formula, ABX3, (A = CH3NH3+; B = Pb2+ or Sn2+; X = Cl, Br and I) have been demonstrated outstanding electrical and optical characteristics, such as high absorption in the visible light region, and long carrier diffusion length [1–7]. Owing to such characteristics, they can be applied for solar cells with power conversion efficiency up 25.2% [8]. Perovskite light-emitting diodes (LEDs) and laser have also been investigated widely because of their outstanding performance [9–16]. Unfortunately, these hybrid perovskites easily react with moisture in air ambient and dissolve because the hydrogen-bonding between its monovalent organic cation and octahedral PbI2 is really weak [17,18]. Thus, their practical application in optoelectronic devices shall be greatly limited. Recently, substituting the organic cation by inorganic Cs+ to fabricate an all-inorganic perovskite (CsPbX3, X = Cl, Br, I) is effective for improving stability under ambient condition. It has also been demonstrated intense photoluminescence (PL), tunable emission wavelength by substituting the chemical composition of halide element, high photoluminescence quantum yields (PLQY, 50-90%) and other advantageous characteristics of perovskites as stated above [19–22].
Due to the high optical gain coefficient and long diffusion length of exciton, the lasing action from micro- and nano-sized optical cavities based on all-inorganic perovskite materials has been studied intensively [23–25]. The symmetrical micro- and nano-structural perovskites with high crystalline quality could serve as resonant cavities and gain medium for lasing, where the photon is confined in Fabry-Perot (FP) mode and/or whispering-gallery mode (WGM) [24,26,27]. Apart from that, random lasing (RL) actions have also been explored in the micro-/nanostructured halide perovskite films [28–34]. Unlike FP or WGM lasers, where the gain medium is inside a well-defined resonant cavity, optical feedback in RLs originates from the multiple light scattering in disordered amplifying media. The RLs show low spatial coherence because the random scattering produces many uncorrelated optical modes emitting in all directions. Another unique advantage of RLs lies in their low-cost and simple processing technique as they can be realized by deposited high optical gain material on the surfaces of arbitrary shapes. Consequently, the RL is a promising light source for the intense laser illumination and speckle-free imaging without the drawback of coherent artifacts [34].
Although perovskite RLs have been studied so far, the research on the CsPbI3 RLs is still rare. For further lighting application, a detailed investigation of the RL characteristics in the CsPbI3 thin films is required. Currently, solution processing-based technique is the most widely used technique for the synthesis of the perovskite films [35,36]. However, the purity of the perovskite by solution-process compromised by unintentional impurities is an issue. The vapor deposition is an alternative method to synthesize high-quality perovskite materials with large size grains [7,11,18]. Some advantages are gained by the vapor process, such as ease of patterning and material compatibility. Moreover, it is reported that the enlarged crystalline size and/or reduction in the fraction of the grain boundaries can obviously improve the performance of the solar cells. In this work, we demonstrated a stable CsPbI3 RL at room temperature. We used a chemical vapor deposition (CVD) method to synthesize CsPbI3 thin films on mica substrates. The CsPbI3 thin films were characterized structurally and optically by scanning electronic microscope (SEM), X-ray diffraction (XRD) patterns and PL measurement. By power-dependent PL measurement, we observed CsPbI3 lasing at room temperature and classified it as RL by angle-dependent PL. Based on the analysis of the fast Fourier transform (FFT) spectra, we could estimate the effective cavity length of the CsPbI3 RL. The lasing stability of the CsPbI3 RL was also investigated. Without protection and passivation, the CsPbI3 thin film could sustain over 105 laser shots in air ambient. This robust perovskite laser is a promising light source in the future.
2. Experimental setup
2.1. Perovskite fabrication
The CVD method was utilized to synthesize CsPbI3 thin films on mica substrates. A quartz tube was mounted on a single-zone furnace. CsI (99.9%, Aldrich) and PbI2 (99.999%, Aldrich) powder with a molar ratio of 1:2 were placed in an alumina boat the center and upstream region (approximately 4 cm away from the center) inside the quartz tube, respectively. The air-cleaved mica substrates were located at 8 cm away from the center in the downstream region. The quartz tube was initially evacuated to 0.5 Torr. The growth temperature and pressure were set and stabilized to 500°C and 6.5 torr followed by a 30 sccm of high purity Ar, respectively. The temperature inside the tube was heated to 500 °C for 20 minutes and kept for 80 minutes. After the procedure of the crystal growth, the furnace was let cool down naturally to room temperature.
2.2. Measurements
The morphology of the thin films was characterized by a field emission scanning electron microscope (ZEISS SUPRA 55). The crystal structure of the layer was conducted using an X-ray diffractometer with Cu Kα radiation (Bruker AXS Gmbh, D8 DISCOVER with GADDS). The 355 nm pulsed laser (350 ps, 1 kHz) was utilized as an excitation source. The laser light was introduced into a 10X objective lens then focused on the sample surface with a spot of 10 μm. The PL emission signal was collected from the same objective lens into a Horiba iHR320 spectrometer equipped with a liquid-nitrogen-cooled CCD array detector. For angle-dependent PL measurement, the PL signal was collected by an optical fiber bundle. All measurements were conducted in an ambient atmosphere at room temperature. The CsPbI3 thin film was directly exposed in the air without any protection and/or passivation.
3. Experimental results
Figure 1(a) shows the typical morphology of the CsPbI3 thin film consisting of irregular grains larger than 1 μm in diameter. The thickness of the thin film was about 2 μm. The XRD analysis of the thin film is shown in Fig. 1(b). The result of the XRD patterns revealed that the thin film is high purity γ-CsPbI3 phase with orthorhombic structure (JCPDS No. 19-0376), and crystalline faces are indexed in Fig. 1(b).
Fig. 1. (a) SEM image of the CsPbI3 thin film. (b) XRD patterns of the CsPbI3 thin film and the XRD standard line for γ-CsPbI3 (JCPDS card No. 18-0376).
Figure 2 shows the absorbance and steady-state PL emission of CsPbI3 thin film. The PL emission was centered at around 701 nm with FWHM of 45 nm, which was consistent with the absorption onset. Therefore, the broad spontaneous emission peak can be attributed to the near band-edge transition [24].
Figure 3(a) shows the lasing spectra of the CsPbI3 thin film under different excitation fluence. Under low optical excitation fluence, only very broad spontaneous emission spectra can be observed with the spectra centered at ∼700 nm. As excitation fluence increases, a sharp peak at 720.7 nm emerge from the broad spontaneous emission spectrum was observed. As the excitation fluence increases, multiple spikes between 715 and 722 nm can be detected. The dependence of the emission intensity on the excitation fluence is plotted in Fig. 3(b), and the observed non-linear increase of the emission intensity is also an indication of the lasing action from the CsPbI3 thin film and the corresponding lasing threshold is determined to be 47.1 mJ/cm2. Figure 3(c) shows the zoom-in lasing spectra from 718.2 nm to 719.4 nm just well above the lasing threshold. We deduced the Q factor from the peak located at 718.8 nm. The peak at 718.8 nm with the Lorentz fitting curve is shown in Fig. 3(d). The FWHM of lasing emission is 0.1 nm, and the corresponding Q factor is calculated to be 7188.
Fig. 3. (a) Lasing spectra of the CsPbI3 thin film under increasing excitation fluence. (b) PL intensity and FWHM of the CsPbI3 thin film as a function of excitation fluence. (c) The zoom-in lasing spectra from 718.2 nm to 719.4 nm just well above threshold. (d) The lasing spectrum at 718.8 nm near threshold with the Lorentz fitting curve.
In the Fig. 3 (c), the lasing peak positions were not regular, which could be an occurrence of a RL. Owing to the lack of well-established laser cavities in the CsPbI3 film, the lasing behavior might originate from the random scattering in the thin film. Figure 4(a) shows a schematic diagram to illustrate the principle of random lasing. In the case of the high gain and strong scattering in the thin film, recurrent scattering events occur [31,34,37–40]. Then, the closed-loop paths will be formed when the excitation fluence goes above a certain threshold. Since different closed-loop paths formed multiple scattering, the RL could be observed in all directions. To verify our assumption, we investigated the lasing behavior of CsPbI3 thin film by angle-dependent PL measurement. Figure 4(b) presents the lasing spectra of the CsPbI3 film observed at two different collection angles. The lasing modes varied with the observation angle. Different RL cavities formed by multiple scattering paths could have different output directions. Thus, lasing modes observed at different angles will be different. This feature of the emission qualitatively confirms that the distinct sharp peaks of a RL action with coherent feedback in the CsPbI3 thin film. The observation of NIR lasing can be attributed to the high quality and thus high optical gain of our sample, which indicates the potential optoelectronic applications of such material system.
Fig. 4. (a) Schematic diagram to illustrate the principle of random lasing. (b) Angle-dependent lasing spectra of the CsPbI3 film in two directions: (a) 0$^\circ $ and (b) 30$^\circ $. form the surface of the CsPbI3 thin film.
To gain further insight into the random cavities of the CsPbI3 thin film, we performed a FFT analysis for the lasing spectra (Fig. 3(a)), as shown in Fig. 5. Notably, the Fourier harmonics become pronounced with increasing excitation fluence, indicates that the close loops formed by multiple scattering establish spatial localization of the RL cavity. Also, the number of peaks of the FFT spectra increases with increasing the excitation fluence, which implies that more and more random lasing cavity achieves the oscillation threshold and begins to lase.The FFT spectrum of a well-established laser cavity has several sharp Fourier harmonics decided by the equation dm = mLcn/π where dm is the Fourier harmonics; m is the order of the Fourier harmonic; Lc is the effective optical cavity length, and n is the refractive index of the RL system [41,42]. The optical cavity length can be determined easily through this equation. Herein, we substituted the first sharp peak, d1 = 20.80 μm (under excitation fluence of 95.5 mJ/cm2). The refractive index of the CsPbI3 RL system, n, is about 2.00 [43]. The optical cavity length of the CsPbI3 RL is calculated to be 32.67 μm. Moreover, the optical cavity length became shorter under the higher excitation fluence. We suggest that the decrease in scattering photons under lower excitation fluence makes the RL hardly occurs if the cavity length maintains the same size. Thus, the cavity length must get longer to reach the sufficient gain.
Meanwhile, the lasing stability is an important issue for commercialization. Therefore, we investigated the stability of the CsPbI3 RL. Figure 6(a) is the lasing evolution of the CsPbI3 thin film under a fixed density excitation, 1.2 Pth (Pth = 61.1 mJ/cm2), and Fig. 6(b) shows the lasing intensity of the CsPbI3 thin film as a function of laser shots. The CsPbI3 RL without protection or passivation on the surface of the thin film could be able to withstand more than 4.8 X 105 laser shots. The high photo-stability might originate from all-inorganic compositions and the small portion of the grain boundary of our thin films [18,26,44]. Owing to substituting the organic cation by inorganic Cs+, CsPbI3 hardly reacts with moisture and dissolve in air ambient. The moisture hardly gets into the inner of the CsPbI3 thin films results from the high-quality perovskite thin film with large grain size and few grain boundaries. Although the solution-process perovskites also show outstanding lasing stability, the complex fabrication and passivation are required [31,33,34]. Thus, our thin film by CVD has a prolonged lasing stability easily without any protection or passivation in the air ambient.
Fig. 6. (a) Lasing spectra of the CsPbI3 thin film during different time under a fixed excitation energy density. (b) Lasing intensity of the CsPbI3 thin film as a function of laser shots.
4. Conclusions
In summary, we successfully synthesized γ-CsPbI3 thin film with an excellent crystalline quality and high purity via CVD. The RL was observed at room temperature with the Q factor over 7000. Through the FFT spectra of the RL, the cavity length was determined about 32.67 μm. Without protection and passivation, the lasing stability test in ambient atmosphere demonstrates superior performance due to the all-inorganic compositions and the small portion of the grain boundary. Our investigations demonstrate the unique lasing properties of CsPbI3 thin films, which might be useful for a practical light source in near future.
Funding
Ministry of Science and Technology, Taiwan (108-2112-M-006-005); Ministry of Education, Taiwan.
Disclosures
The authors declare no conflicts of interest.
References
1. D. B. Mitzi, C. A. Feild, Z. Schlesinger, and R. B. Laibowitz, “Transport, Optical, and Magnetic Properties of the Conducting Halide Perovskite CH3NH3SnI3,” J. Solid State Chem. 114(1), 159–163 (1995). [CrossRef]
2. A. Kojima, K. Teshima, Y. Shirai, and T. Miyasaka, “Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells,” J. Am. Chem. Soc. 131(17), 6050–6051 (2009). [CrossRef]
3. G. Xing, N. Mathews, S. Sun, S. S. Lim, Y. M. Lam, M. Grätzel, S. Mhaisalkar, and T. C. Sum, “Long-Range Balanced Electron- and Hole-Transport Lengths in Organic-Inorganic CH3NH3PbI3,” Science 342(6156), 344–347 (2013). [CrossRef]
4. C. Wehrenfennig, G. E. Eperon, M. B. Johnston, H. J. Snaith, and L. M. Herz, “High Charge Carrier Mobilities and Lifetimes in Organolead Trihalide Perovskites,” Adv. Mater. 26(10), 1584–1589 (2014). [CrossRef]
5. A. Amat, E. Mosconi, E. Ronca, C. Quarti, P. Umari, M. K. Nazeeruddin, M. Grätzel, and F. De Angelis, “Cation-Induced Band-Gap Tuning in Organohalide Perovskites: Interplay of Spin–Orbit Coupling and Octahedra Tilting,” Nano Lett. 14(6), 3608–3616 (2014). [CrossRef]
6. M. B. Price, J. Butkus, T. C. Jellicoe, A. Sadhanala, A. Briane, J. E. Halpert, K. Broch, J. M. Hodgkiss, R. H. Friend, and F. Deschler, “Hot-carrier cooling and photoinduced refractive index changes in organic–inorganic lead halide perovskites,” Nat. Commun. 6(1), 8420 (2015). [CrossRef]
7. Z. Liu, Y. Li, X. Guan, Y. Mi, A. Al-Hussain, S. T. Ha, M. H. Chiu, C. Ma, M. R. Amer, L. J. Li, J. Liu, Q. Xiong, J. Wang, X. Liu, and T. Wu, “One-Step Vapor-Phase Synthesis and Quantum-Confined Exciton in Single-Crystal Platelets of Hybrid Halide Perovskites,” J. Phys. Chem. Lett. 10(10), 2363–2371 (2019). [CrossRef]
8. N. R. E. Laboratory, “Best Research-Cell Efficiency Chart, https://www.nrel.gov/pv/cell, accessed: April, 2020,” (2020).
9. G. Xing, N. Mathews, S. S. Lim, N. Yantara, X. Liu, D. Sabba, M. Grätzel, S. Mhaisalkar, and T. C. Sum, “Low-temperature solution-processed wavelength-tunable perovskites for lasing,” Nat. Mater. 13(5), 476–480 (2014). [CrossRef]
10. Z. K. Tan, R. S. Moghaddam, M. L. Lai, P. Docampo, R. Higler, F. Deschler, M. Price, A. Sadhanala, L. M. Pazos, D. Credgington, F. Hanusch, T. Bein, H. J. Snaith, and R. H. Friend, “Bright light-emitting diodes based on organometal halide perovskite,” Nat. Nanotechnol. 9(9), 687–692 (2014). [CrossRef]
11. Q. Zhang, S. T. Ha, X. Liu, T. C. Sum, and Q. Xiong, “Room-Temperature Near-Infrared High-Q Perovskite Whispering-Gallery Planar Nanolasers,” Nano Lett. 14(10), 5995–6001 (2014). [CrossRef]
12. H. Zhu, Y. Fu, F. Meng, X. Wu, Z. Gong, Q. Ding, M. V. Gustafsson, M. T. Trinh, S. Jin, and X. Y. Zhu, “Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors,” Nat. Mater. 14(6), 636–642 (2015). [CrossRef]
13. G. R. Li, Z. K. Tan, D. W. Di, M. L. Lai, L. Jiang, J. H. W. Lim, R. H. Friend, and N. C. Greenham, “Efficient Light-Emitting Diodes Based on Nanocrystalline Perovskite in a Dielectric Polymer Matrix,” Nano Lett. 15(4), 2640–2644 (2015). [CrossRef]
14. P. Perumal, C. S. Wang, K. M. Boopathi, G. Haider, W. C. Liao, and Y. F. Chen, “Whispering Gallery Mode Lasing from Self-Assembled Hexagonal Perovskite Single Crystals and Porous Thin Films Decorated by Dielectric Spherical Resonators,” ACS Photonics 4(1), 146–155 (2017). [CrossRef]
15. L. N. Quan, B. P. Rand, R. H. Friend, S. G. Mhaisalkar, T. W. Lee, and E. H. Sargent, “Perovskites for Next-Generation Optical Sources,” Chem. Rev. 119(12), 7444–7477 (2019). [CrossRef]
16. K. Wang, S. Wang, S. Xiao, and Q. Song, “Recent Advances in Perovskite Micro- and Nanolasers,” Adv. Opt. Mater. 6(18), 1800278 (2018). [CrossRef]
17. H. Masaki, H. Yoichi, N. Ryota, M. Tomoya, A. Ulugbek, O. Hiromi, N. Takeshi, Y. Yoshifumi, and H. Yasuhiko, “In-situ X-ray diffraction reveals the degradation of crystalline CH3NH3PbI3 by water-molecule collisions at room temperature,” Jpn. J. Appl. Phys. 57(2), 028001 (2018). [CrossRef]
18. Z. Y. Wu, B. L. Jian, and H. C. Hsu, “Photoluminescence characterizations of highly ambient-air-stable CH3NH3PbI3/PbI2 heterostructure,” Opt. Mater. Express 9(4), 1882–1892 (2019). [CrossRef]
19. L. Protesescu, S. Yakunin, M. I. Bodnarchuk, F. Krieg, R. Caputo, C. H. Hendon, R. X. Yang, A. Walsh, and M. V. Kovalenko, “Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut,” Nano Lett. 15(6), 3692–3696 (2015). [CrossRef]
20. I. Lignos, S. Stavrakis, G. Nedelcu, L. Protesescu, A. J. deMello, and M. V. Kovalenko, “Synthesis of Cesium Lead Halide Perovskite Nanocrystals in a Droplet-Based Microfluidic Platform: Fast Parametric Space Mapping,” Nano Lett. 16(3), 1869–1877 (2016). [CrossRef]
21. K. H. Wang, Y. Peng, J. Ge, S. Jiang, B. S. Zhu, J. Yao, Y. C. Yin, J. N. Yang, Q. Zhang, and H. B. Yao, “Efficient and Color-Tunable Quasi-2D CsPbBrxCl3−x Perovskite Blue Light-Emitting Diodes,” ACS Photonics 6(3), 667–676 (2019). [CrossRef]
22. S. Seth, T. Ahmed, A. De, and A. Samanta, “Tackling the Defects, Stability, and Photoluminescence of CsPbX3 Perovskite Nanocrystals,” ACS Energy Lett. 4(7), 1610–1618 (2019). [CrossRef]
23. Y. Fu, H. Zhu, C. C. Stoumpos, Q. Ding, J. Wang, M. G. Kanatzidis, X. Zhu, and S. Jin, “Broad Wavelength Tunable Robust Lasing from Single-Crystal Nanowires of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I),” ACS Nano 10(8), 7963–7972 (2016). [CrossRef]
24. H. Zhou, S. Yuan, X. Wang, T. Xu, X. Wang, H. Li, W. Zheng, P. Fan, Y. Li, L. Sun, and A. Pan, “Vapor Growth and Tunable Lasing of Band Gap Engineered Cesium Lead Halide Perovskite Micro/Nanorods with Triangular Cross Section,” ACS Nano 11(2), 1189–1195 (2017). [CrossRef]
25. B. Zhou, M. Jiang, H. Dong, W. Zheng, Y. Huang, J. Han, A. Pan, and L. Zhang, “High-Temperature Upconverted Single-Mode Lasing in 3D Fully Inorganic Perovskite Microcubic Cavity,” ACS Photonics 6(3), 793–801 (2019). [CrossRef]
26. Q. Zhang, R. Su, X. Liu, J. Xing, T. C. Sum, and Q. Xiong, “High-Quality Whispering-Gallery-Mode Lasing from Cesium Lead Halide Perovskite Nanoplatelets,” Adv. Funct. Mater. 26(34), 6238–6245 (2016). [CrossRef]
27. B. Tang, H. Dong, L. Sun, W. Zheng, Q. Wang, F. Sun, X. Jiang, A. Pan, and L. Zhang, “Single-Mode Lasers Based on Cesium Lead Halide Perovskite Submicron Spheres,” ACS Nano 11(11), 10681–10688 (2017). [CrossRef]
28. T. S. Kao, Y. H. Chou, C. H. Chou, F. C. Chen, and T. C. Lu, “Lasing behaviors upon phase transition in solution-processed perovskite thin films,” Appl. Phys. Lett. 105(23), 231108 (2014). [CrossRef]
29. R. Dhanker, A. N. Brigeman, A. V. Larsen, R. J. Stewart, J. B. Asbury, and N. C. Giebink, “Random lasing in organo-lead halide perovskite microcrystal networks,” Appl. Phys. Lett. 105(15), 151112 (2014). [CrossRef]
30. S. Yakunin, L. Protesescu, F. Krieg, M. I. Bodnarchuk, G. Nedelcu, M. Humer, G. De Luca, M. Fiebig, W. Heiss, and M. V. Kovalenko, “Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites,” Nat. Commun. 6(1), 8056 (2015). [CrossRef]
31. Z. F. Shi, X. G. Sun, D. Wu, T. T. Xu, Y. T. Tian, Y. T. Zhang, X. J. Li, and G. T. Du, “Near-infrared random lasing realized in a perovskite CH3NH3PbI3 thin film,” J. Mater. Chem. C 4(36), 8373–8379 (2016). [CrossRef]
32. C. Li, Z. Zang, C. Han, Z. Hu, X. Tang, J. Du, Y. Leng, and K. Sun, “Highly compact CsPbBr3 perovskite thin films decorated by ZnO nanoparticles for enhanced random lasing,” Nano Energy 40, 195–202 (2017). [CrossRef]
33. A. Safdar, Y. Wang, and T. F. Krauss, “Random lasing in uniform perovskite thin films,” Opt. Express 26(2), A75–A84 (2018). [CrossRef]
34. Y. C. Wang, H. Li, Y. H. Hong, K. B. Hong, F. C. Chen, C. H. Hsu, R. K. Lee, C. Conti, T. S. Kao, and T. C. Lu, “Flexible Organometal–Halide Perovskite Lasers for Speckle Reduction in Imaging Projection,” ACS Nano 13(5), 5421–5429 (2019). [CrossRef]
35. C. H. Chiang, T. Y. Li, H. S. Wu, K. Y. Li, C. F. Hsu, L. F. Tsai, P. K. Yang, Y. J. Lee, H. C. Lee, C. Y. Wang, and M. L. Tsai, “High-stability inorganic perovskite quantum dot–cellulose nanocrystal hybrid films,” Nanotechnology 31(32), 324002 (2020). [CrossRef]
36. H. L. Hsu, B. H. Jiang, C. L. Chung, Y. Y. Yu, R. J. Jeng, and C. P. Chen, “Commercially available jeffamine additives for p–i–n perovskite solar cells,” Nanotechnology 31(27), 274002 (2020). [CrossRef]
37. P. W. Anderson, “Absence of Diffusion in Certain Random Lattices,” Phys. Rev. 109(5), 1492–1505 (1958). [CrossRef]
38. D. S. Wiersma, P. Bartolini, A. Lagendijk, and R. Righini, “Localization of light in a disordered medium,” Nature 390(6661), 671–673 (1997). [CrossRef]
39. H. Cao, Y. G. Zhao, S. T. Ho, E. W. Seelig, Q. H. Wang, and R. P. H. Chang, “Random Laser Action in Semiconductor Powder,” Phys. Rev. Lett. 82(11), 2278–2281 (1999). [CrossRef]
40. D. S. Wiersma, “Random lasers explained?” Nat. Photonics 3(5), 246–248 (2009). [CrossRef]
41. Y. Ren, H. Zhu, Y. Wu, G. Lou, Y. Liang, S. Li, S. Su, X. Gui, Z. Qiu, and Z. Tang, “Ultraviolet Random Laser Based on a Single GaN Microwire,” ACS Photonics 5(6), 2503–2508 (2018). [CrossRef]
42. Y. J. Lee, T. W. Yeh, P. Nagarjuna, C. C. Tseng, and J. Y. Yi, “A strain-gauge random laser,” APL Mater. 7(6), 061103 (2019). [CrossRef]
43. R. K. Singh, R. Kumar, N. Jain, S. R. Dash, J. Singh, and A. Srivastava, “Investigation of optical and dielectric properties of CsPbI3 inorganic lead iodide perovskite thin film,” J. Taiwan Inst. Chem. Eng. 96, 538–542 (2019). [CrossRef]
44. J. Song, J. Li, X. Li, L. Xu, Y. Dong, and H. Zeng, “Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3),” Adv. Mater. 27(44), 7162–7167 (2015). [CrossRef]
