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Apr 23, 2017 - ABSTRACT: Perovskite nanocrystals open up a bright future for nanolasers, for their various instinct advantages (such as large absorpti...
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Up-Conversion Perovskite Nanolaser With Single Mode and Low Threshold Chao Huang, Kunyi Wang, Zhong-Jian Yang, Li Jiang, Renming Liu, Rongling Su, Zhang-Kai Zhou, and Xue-Hua Wang J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 23 Apr 2017 Downloaded from http://pubs.acs.org on April 23, 2017

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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.

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Up-Conversion Perovskite Nanolaser with Single Mode and Low Threshold Chao Huang†,‡, Kunyi Wang†,‡, Zhongjian Yangǁ, Li Jiang†, Renming Liu†, Rongling Su†, ZhangKai Zhou†,*, and Xuehua Wang† †School of Physics, State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, China ǁHunan Key Laboratory of Super Microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, Hunan 410083, China *E-mail: [email protected] ABSTRACT. Perovskite nanocrystals open up bright future for nanolasers, for their various instinct advantages (such as large absorption cross section and optical gain, high fluorescence quantum yields, etc.) can greatly benefit the design and fabrication of nanolasers with low threshold, high emission efficiency and well integration. Although numerous investigation efforts have been devoted into exploring the perovskite nanolaser of single-photon-pumped type, the study of up-conversion lasing excited by two-photon-pumping is still established on the structures of micrometer scale with multiple mode, which is not in favor of improving the working stability and scale miniaturization of future nanolasers. In order to expand the application of perovskite nanocrystal in nanolasers, we studied the perovskite (CsPbX3, X = Cl, Br) nanoplates fabricated by supersaturated recrystallization approach, and observed single mode up-conversion lasing from single nanoplate with low threshold of 4.84 µJ/cm2. In addition,

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theoretical calculations demonstrated that such single mode lasing could be attributed to the whispering gallery mode supported by the nanoplate cavity. Our findings not only prove the great potentials of perovskite nanoplate in building up-conversion nanolaser, but also further our understanding of lasing behaviors in nanoscale perovskite materials. 1. Introduction Semiconductor nanocrystals (NCs) hold the key to cultivate applications of various functional devices, such as laser components of miniaturization in integrated nanolasers,1–3 high-throughput sensing4 and optical communications.5 Specially, in the exploration of nanolaser based on semiconductor NCs, generally two types are investigated. One is the single-photon-pumped (SPP) laser with ultraviolet (UV) light sources.6–8 However, the UV excitations have destructive effects to samples, and the problem of short penetration depth, limiting their developments especially in biomedical imaging and sensing.9,10 The other one is the two-photon-pumped (TPP) laser of up-conversion type, which is a promising avenue for passing the above issues.11–14 In comparison with SPP, TPP with infrared excitation possesses several unique properties such as longer penetration depth, as well as reduced photo-damage and photo-bleaching.11,15,16 In addition, TPP process has fascinating characteristics for direct applications including avoiding unwanted scattering and absorption losses. These advantages enable the TPP to be used to stabilize the laser pulse, and provide a route to actualize frequency up-conversion within a broad spectral region.12–14 So, TPP is a viable and important technique to generate coherent light by using colloidal semiconductor NCs. However, the small two-photon-absorption (TPA) cross section, low fluorescence quantum yields (QY) and fast Auger recombination in semiconductor NCs hinder future developments of

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practical TPP lasers based on colloidal semiconductor NC.11,12,17 Thus, it is highly desired to find a new type of semiconductor materials to overcome above problems. Recently, perovskite NCs of lead halide semiconductors have emerged as a promising family for their unique optoelectronic properties, which have been constructed into applications including solar cells, photodetectors, light-emitting diodes, and nanolasers.18–23 The new NCs have key characteristics which make them superior in TPP lasers such as large TPA cross section,24,25 large optical gain,26–28 high fluorescence QY,29–32 slow Auger recombination,33 long carrier diffusion length34,35 and wide color gamut.36,37 Due to these good merits, great achievements of nanolaser based on perovskite NCs have been achieved. But, this field still faces three crucial challenges, which are to decrease the lasing threshold, find single mode laser, and reduce the size of the lasing NCs down to nanoscale. Moreover, in order to match industrial fabrication requirements of high stability and device miniaturization, these three challenges are urgent to be addressed. So, it is strongly needed to realize the up-conversion lasing of single mode on nanoscale perovskite structure with low threshold. Herein we demonstrate the feasibility of using perovskite semiconductor NCs to tackle present challenges of TPP nanolasers. CsPbX3 (X = Cl, Br) plates with edge length and thickness in nanoscale are fabricated by supersaturated recrystallization. The naturally formed perovskite nanoplate can sustain whispering gallery mode, leading to TPP lasing of single mode with threshold as low as 4.84 µJ/cm2. Although our experiments are performed at liquid-nitrogen temperature, such threshold is 1 order of magnitude lower than the best results ever reported from perovskite cubes in micrometer scale at room temperature.24,25 Moreover, both theoretical and experimental investigation are carried out to study the size dependence on single mode and multiple mode laser actions of perovskite nanoplates.

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2. Experimental Methods Synthesis of CsPbX3 NCs with supersaturated recrystallization. All the materials including Lead (II) bromideide (PbBr2, >99.9%), Cesium bromide (CsBr, >99%), Dimethyl sulfoxide ((CH3)2SO, DMSO, >99%), Oleylamine (OAm, >98%), Oleic acid (OA, >99%), Toluene (C6H5CH3, >99.8%) were purchased from Sigma Aldrich and used as received. Colloidal CsPbBr3 NCs were synthesized by modifying the procedure by Haibo Zeng and co-workers.38 1 mL PbBr2 (0.1 mmol dissolved in 1 mL of DMSO) and 1 mL CsBr (0.1 mmol dissolved in 1 mL of DMSO) was loaded into a flask. Then, OA (0.2 mL) and OAm (0.1mL) as modifier were added. After that, 100 µL of the mixture was swiftly added into toluene (10 mL) under magnetically stirring, and gradually the color of mixing solution turned to bright green. Other samples with different colors were fabricated with the different mixture ratio of PbX2 and CsX (X = Cl, Br). The manipulations were implemented at room temperature. Instrumentation and measurements. The absorption spectra were collected using an ultraviolet-visible-near-infrared (UV-VIS-NIR) spectrophotometer (Lambda 950, PerkinElmer). The reference we adopted was 3 mL toluene. The scanning electron microscopy (SEM) images were taken by a Zeiss Auriga-39-34 (Oberkchen, Germany) microscope operated at 5.0 kV. The transmission electron microscopy (TEM) graph was performed by using a JEOL 2010HT TEM machine operated at 120 kV. The high-resolution TEM (HRTEM) images and selected-area electron diffraction (SEAD) patterns were taken by Titan G2 30-3000 (FEI) working at 300 kV. The atomic force microscopy (AFM) images were taken by a Dimension FastScan bio (Bruker, USA). The powder X-ray diffraction (XRD) data were collected using a diffractometer (Empyrean, PANalytical) with Cu Kα radiation. Photoluminescence characterizations were performed with two-photon excitations by femtosecond pulses from a Ti:sapphire laser (MaiTai,

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Spectra Physics, 79MHz, 100fs). The PL from the sample was collected using a liquid-nitrogencooled Charge-Coupled Device (CCD, SPEC-10, Princeton Instrument). Electron-Multiplying CCD (EMCCD, Andor iXon Ultra) was used for the sample location. Computational simulations. The simulation results were calculated with Finite-difference Time-domain (FDTD) method, using a commercially available FDTD simulation software package from Lumerical Solutions. A dipole was used as the excitation light source. The perovskite cavity was simulated using 2D square system (edge length 515 nm, mesh 1 nm, perfectly matched layer boundary conditions) and refractive index of CsPbBr2Cl is set to be 2.46. The refractive index of perovskite is selected according to previous literatures.24,25,39 3. Results and discussion Our perovskite nanoplates of CsPbX3 were prepared under room temperature conditions using supersaturated recrystallization (SR). The schematic illustration of the detailed process is shown in Figure 1a. Firstly, PbX2 and CsX (X = Cl, Br) were selected as ion sources to dissolve in DMSO, while OA and OAm were used as surface ligands. After CsX had been mixed with PbX2 (i), the agents of OA and OAm were added (ii) to make them serve as precursors for further grown. Then, the mixture was added into toluene (iii), and as the reaction proceeded, the solution gradually changed its color and finally turned to bright green as illustrated in the insert picture of Figure 1a. The scheme of obtained perovskite lead halide NC is shown in Figure 1b, where one can see the atomic ratio of all the samples is almost 1:1:3 (Cs: Pb: X), and the ratio of Cl and Br can be adjusted by controlling the mixing ratio of PbX2 and CsX. In addition, more vivid morphology information about our samples is given in Figure 1c-e (the sample of CsPbBr2Cl nanoplate was taken as an example). Figure 1c is an SEM image of the sample of CsPbBr2Cl nanoplate, showing the presence of rather monodisperse cubic and squared NCs with

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an edge length of 400-800 nm. Such size is comparable to the excitation wavelength and can lead to cavity effects which benefit laser emission demonstrated and discussed later. The AFM result in Figure 1d shows the smooth surface with a roughness of only ~ 5.0 nm and a cross section height within nanoscale of ~150 nm. As indicated by AFM, the obtained perovskite nanoplates of CsPbBr2Cl can be regarded as perfectly flat in optical level. Also, as the HRTEM image (Figure 1e, which is taken from the nanoplate showing in the insert of Figure 1c), as well as the selected-area electron diffraction (SAED) pattern (insert of Figure 1e), confirms that the CsPbBr2Cl NCs have a high crystalline quality with the lattice of 0.58 nm. Furthermore, in order to identify the crystal phase of our sample, the powder XRD was performed. As the spectra in Figure 1f shown, orthorhombic phase of CsPbX3 (X = Br, Cl) NCs can be found, since the XRD pattern features of our samples match the standard data very well (the last two data in Figure 1f).

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Figure 1. Preparation and morphology of our samples. a, the preparation procedures of perovskite nanoplates of CsPbX3; b, the scheme of the nanostructure of perovskite lead halide nanocrystal; c, typical SEM and TEM (the insert picture) images showing the morphology of perovskite nanoplate in low and high magnifications, respectively (the scale bar of insert is 100 nm); d, AFM measurement results of a typical single perovskite (CsPbBr2Cl) nanoplate, showing the thickness is about 150 nm; e, HRTEM and SEAD results of a single CsPbBr2Cl nanoplate, demonstrating a high crystalline quality with the lattice of 0.58 nm; f, powder XRD results further confirmed the orthorhombic phase of CsPbX3. After sample preparation, we began our optical study from ensembles at room temperature. It is easy to find that the optical absorption and emission properties of colloidal CsPbX3 NCs can be effectively and extensively tuned by adjusting the ratio of halides in mixed halide NCs. As vividly exhibited in Figure 2a, SR-formed CsPbX3 (X = Br, Cl) NCs colloids emit 3 different bright colors under hand-holding UV light illumination. To specific, when Cl anions were added into the reaction system of CsPbX3 to increase the ratio of Cl anion from 0 to ~33.3%, both the absorption edges and TPP photoluminescence (PL) peaks blue shift (Figure 2b). Since the edge of absorption curve (solid) locates near the PL peak (dashed line) for every sample, both of absorption edge and PL peak move from ~520 to ~480 nm, covering the green to blue spectral range. In addition, optical measurements of excitation dependence on up-conversion PL intensity were done sequentially. Figure 2c gives the PL spectra of TPP observed from colloidal CsPbBr2Cl NCs under different excitation energies but the same incident wavelength of 800 nm. From this picture, one can see narrow emission line with the full-width at half-maximum (FWHM) of 17 nm. Furthermore, with the increasing of excitation power, the emission behaviors of all the three samples follow quadratic dependences with slopes ν (ν = logIPL/logIexc) of ~2.05, strongly suggesting TPP PL process (Figure 2d).40,41

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Figure 2. Optical measurements of colloidal ensemble samples in room temperature. a, a photon image of CsPbX3 (X = Br, Cl) NC solution illuminated by a hand-holding UV light, showing three different bright lights; b, the absorption and PL properties of the colloidal CsPbX3 NC solution, in which one can see the edge of absorption curve (solid) locates near the PL peak (dashed line) for each sample (sample i, ii, and iii are the same in figure a and b); c, upconversion PL spectra of colloidal CsPbBr2Cl NCs; d, the excitation dependence on upconversion PL of three different samples, from the fitting results of which nearly the same slope ν of ~2.05 can be found. Following the optical measurements at room temperature, we turned to study the TPP lasing of a single perovskite (CsPbBr2Cl) NC under 77 K. In order to locate one single NC, we carefully compared the SEM image and the optical image obtained by our EMCCD, and from the pattern features of these pictures, we can locate the perovskite NC which the incident laser is focused on (the diameter of focusing area is within 2µm, and experimental details can be found in Figure S1). Figure 3a shows the TPP emission spectra recorded from a single CsPbBr2Cl nanoplate (edge

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length is ~500 nm) with pumping wavelength of 780 nm under different exciting powers. It is clear to find that with the increasing excitation fluence, the perovskite nanoplate laser action is evidenced by sharp emission peak (FWHM is ~2 nm) when the excitation fluence goes over a threshold about 4.84 µJ/cm2, exhibiting a strong single mode lasing emerges as a sharp mode peak of 510 nm. Above the onset power, the peak intensity around 510 nm increases dramatically and superlinearly with the excitation fluence (slope ν = 2.03), demonstrating an obvious knee behavior and a threshold characteristic of a laser (Figure 3b). Thereafter, we further theoretically research the optical modes inside the perovskite NC cavity. Considering the high refractive index contrast between the vacuum and perovskite NC, the low threshold, and the rectangular shape of the perovskite nanoplate, one can anticipate that it is the generated whispering gallery mode (WGM) in the perovskite nanoplate that should be attributed to for our observed laser emission.39 This assumption can be confirmed by the simulated electric fields distributions shown in Figure 3c, where the emission are restricted by the total internal reflection at the interfaces between the NC edge and vacuum (white dashed square shows the shape of perovskite nanoplate), showing WGM oscillation behaviors.24,39 Also, the calculated laser emission spectrum of the single mode is showed in Figure 3d, which is in a good agreement with our experimental result, and further prove our theoretical considerations. One thing should be mentioned is that due to the reason of sample preparation method, it is inevitable that some small particle will be attached on or next to the nanoplate we measured. This situation can be improved by further sample growth investigations, but herein, it is fortunate to find that such small perovskite particles will not bring about laser action because their small size can not support resonant mode that is necessary for laser generation. This conclusion can be confirmed by previous literatures,25,42 experimental results (we measured small particles and no laser emission

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can be observed), and theoretical simulations (Figure S2). Therefore, it is believed that the existence of the small particles will not affect our laser emission observations.

Figure 3. Single mode lasing from one single perovskite (CsPbBr2Cl) nanoplate measured at 77 K. a, the PL spectra of a nanoplate with different excitation intensities and the same incident wavelength of 780 nm, where single mode lasing at 510 nm is observed, and the insert picture is the measured nanoplate with scale bar of 200 nm; b, the excitation dependence on the upconversion emission intensity of the single mode lasing, where a lasing threshold of 4.48 µJ/cm2 and slope of 2.03 are obtained; c, the simulated electric field distributions at the wavelength of 510 nm, demonstrating the generation of WGM in the nanoplate structure; d, the simulated emission spectrum, which agrees well with the experimental result. Despite the single mode lasing, as we went for other single perovskite (CsPbBr2Cl) NCs with larger size, it is found that such perovskite nanoplates can hold multiple emission modes, leading to multi-mode laser actions (typical results can be found in Figure S3). As Figure 4a demonstrated, a three-mode laser emission is observed from a perovskite nanoplate with larger edge length of 580 nm. The simulations of a three mode lasing are shown in Figure S4. After

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investigating the size dependence on lasing behavior, one can find that larger size can result in multi-mode lasing, and the lasing threshold can also be reduced (Figure 4b). So, it is actually easier to realize multi-mode laser in large size perovskite NCs. However, it is more desirable to pursue single mode laser emission in nanoscale structures, which can better match the purpose of miniaturization and stabilization of device. Therefore, it is believed that although we obtain upconversion nanolaser at liquid-nitrogen temperature (higher than 120 K, no obvious laser action can be observed, shown by Figure S5), the good merits of single mode laser emission, low threshold and the small size, can greatly help our perovskite nanoplate find useful applications in the design and fabrication of future nanolaser device.

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Figure 4. Multi-mode lasing of single perovskite (CsPbBr2Cl) nanoplate measured at 77 K. a, the PL spectra of a nanoplate under different excitation fluences, showing three obvious laser modes (the scale bar is 100 nm); b, the statistic results of lasing thresholds and the nanoplate sizes of the samples with different laser modes. 4. Conclusion In conclusion, we have fabricated perovskite NCs of CsPbX3 (X =Cl, Br) in the shape of nanoplate by SR method, and the products were measured to be 400-800 nm in edge length and ~150 nm in thickness, with high crystalline quality of orthorhombic phase. Under TPP, we obtained single mode up-conversion lasing from a single perovskite (CsPbBr2Cl) nanoplate with low threshold of 4.84 µJ/cm2, and the threshold could be further reduced to 3.26 µJ/cm2 if larger nanoplate with multiple mode was measured. One thing should be mentioned is that although multi-mode up-conversion lasing with threshold of ~60 µJ/cm2 has been observed in the system of perovskite microcrystals at room temperature, single mode TPP lasing of single perovskite structure in nanoscale is seldom investigated. With low threshold, nanoscale size, as well as single mode up-conversion lasing property, the perovskite nanoplate is believed to possess bright future in constructing nanolasers. ASSOCIATED CONTENT Supporting Information. The detailed information about how to locate single perovskite NCs, theoretical calculations of laser action, the original data of PL measurement in different single perovskite NCs, and temperature dependence on PL emission of the perovskite NCs are given. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION

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Corresponding Author *To whom correspondence should be addressed. E-mail: [email protected]; Tel: +86020-84113723 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡C. Huang and K. Wang contributed equally. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported in part by Ministry of Science and Technology of China (2016YFA0301300), National Natural Science Foundation of China (61675237), the Guangdong Natural Science Foundation (2014A030313140), and the fundamental research funds for the central universities (16lgjc85). REFERENCES (1) Monat, C.; Domachuk, P.; Eggleton, B. J. Integrated Optofluidics: A New River of Light. Nat. Photon. 2007, 1, 106–114. (2) Psaltis, D.; Quake, S. R.; Yang, C. Developing Optofluidic Technology through the Fusion of Microfluidics and Optics. Nature 2006, 442, 381–386. (3) Fan, X.; White, I. M. Optofluidic Microsystems for Chemical and Biological Analysis. Nat. Photon. 2011, 5, 591–597. (4) Hill, M. T.; Gather, M. C. Advances in Small Lasers. Nat. Photon. 2014, 8, 908–918.

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(5) Lu, Y. J.; Kim, J.; Chen, H. Y.; Wu, C.; Dabidian, N.; Sanders, C. E.; Wang, C. Y.; Lu, M. Y.; Li, B. H.; Qiu, X., et al. Plasmonic Nanolaser Using Epitaxially Grown Silver Film. Science 2012, 337, 450– 453. (6) Zhu, H.; Fu, Y.; Meng, F.; Wu, X.; Gong, Z.; Ding, Q.; Gustafsson, M. V.; Tuan Trinh, M.; Jin, S.; Zhu, X. Y. Lead Halide Perovskite Nanowire Lasers with Low Lasing Thresholds and High Quality Factors. Nat. Mater. 2015, 14, 636–642. (7) Wang, Y.; Li, X.; Song, J.; Xiao, L.; Zeng, H.; Sun, H. All-Inorganic Colloidal Perovskite Quantum Dots: A New Class of Lasing Materials with Favorable Characteristics. Adv. Mater. 2015, 27, 7101–7108. (8) Huang, M. H.; Mao, S.; Feick, H.; Yan, H.; Wu, Y.; Kind, H.; Weber, E.; Russo, R.; Yang, P. RoomTemperature Ultraviolet Nanowire Nanolasers. Science 2001, 292, 1897–1899. (9) Ploschner, M.; Čižmár, T.; Mazilu, M.; Di Falco, A.; Dholakia, K. Bidirectional Optical Sorting of Gold Nanoparticles. Nano Lett. 2012, 12, 1923–1927. (10) Yu, X. F.; Chen, L. D.; Li, M.; Xie, M. Y.; Zhou, L.; Li, Y.; Wang, Q. Q. Highly Efficient Fluorescence of NdF3/SiO2 Core/Shell Nanoparticles and the Applications for in Vivo NIR Detection. Adv. Mater. 2008, 20, 4118–4123. (11) Todescato, F.; Fortunati, I.; Gardin, S.; Garbin, E.; Collini, E.; Bozio, R.; Jasieniak, J. J.; Della Giustina, G.; Brusatin, G.; Toffanin, S., et al. Soft-Lithographed Up-Converted Distributed Feedback Visible Lasers Based on CdSe-CdZnS-ZnS Quantum Dots. Adv. Funct. Mater. 2012, 22, 337–344. (12) Xing, G.; Liao, Y.; Wu, X.; Chakrabortty, S.; Liu, X.; Yeow, E. K. L.; Chan, Y.; Sum, T. C. Ultralow-Threshold Two-Photon Pumped Amplified Spontaneous Emission and Lasing from Seeded CdSe/CdS Nanorod Heterostructures. ACS Nano 2012, 6, 10835–10844. (13) Yu, J.; Cui, Y.; Xu, H.; Yang, Y.; Wang, Z.; Chen, B.; Qian, G. Confinement of Pyridinium Hemicyanine Dye within an Anionic Metal-Organic Framework for Two-Photon-Pumped Lasing. Nat. Commun. 2013, 4, 2719.

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(25) Xu, Y.; Chen, Q.; Zhang, C.; Wang, R.; Wu, H.; Zhang, X.; Xing, G.; Yu, W. W.; Wang, X.; Zhang, Y.; et al. Two-Photon-Pumped Perovskite Semiconductor Nanocrystal Lasers. J. Am. Chem. Soc. 2016, 138, 3761–3768. (26) Li, Y. J.; Lv, Y.; Zou, C. L.; Zhang, W.; Yao, J.; Zhao, Y. S. Output Coupling of Perovskite Lasers from Embedded Nanoscale Plasmonic Waveguides. J. Am. Chem. Soc. 2016, 138, 2122–2125. (27) Luo, B.; Pu, Y. C.; Yang, Y.; Lindley, S. A.; Abdelmageed, G.; Ashry, H.; Li, Y.; Li, X.; Zhang, J. Z. Synthesis, Optical Properties, and Exciton Dynamics of Organolead Bromide Perovskite Nanocrystals. J. Phys. Chem. C 2015, 119, 26672–26682. (28) Guo, Z.; Yoon, S. J.; Manser, J. S.; Kamat, P. V.; Luo, T. Structural Phase- and DegradationDependent Thermal Conductivity of CH3NH3PbI3 Perovskite Thin Films. J. Phys. Chem. C 2016, 120, 6394–6401. (29) Zhang, F.; Zhong, H.; Chen, C.; Wu, X. G.; Hu, X.; Huang, H.; Han, J.; Zou, B.; Dong, Y. Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology. ACS Nano 2015, 9, 4533–4542. (30) Pan, J.; Sarmah, S. P.; Murali, B.; Dursun, I.; Peng, W.; Parida, M. R.; Liu, J.; Sinatra, L.; Alyami, N.; Zhao, C., et al. Air-Stable Surface-Passivated Perovskite Quantum Dots for Ultra-Robust, Single and Two-Photon-Induced Amplified Spontaneous Emission. J. Phys. Chem. Lett. 2015, 6, 5027–5033. (31) Nedelcu, G.; Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Grotevent, M. J.; Kovalenko, M. V. Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3 , X = Cl, Br, I). Nano Lett. 2015, 15, 5635–5640. (32) Dirin, D. N.; Protesescu, L.; Trummer, D.; Kochetygov, I. V.; Yakunin, S.; Krumeich, F.; Stadie, N. P.; Kovalenko, M. V. Harnessing Defect-Tolerance at the Nanoscale: Highly Luminescent Lead Halide Perovskite Nanocrystals in Mesoporous Silica Matrixes. Nano Lett. 2016, 16, 5866–5874. (33) Xing, G.; Mathews, N.; Lim, S. S.; Yantara, N.; Liu, X.; Sabba, D.; Grätzel, M.; Mhaisalkar, S.; Sum, T. C. Low-Temperature Solution-Processed Wavelength-Tunable Perovskites for Lasing. Nat. Mater. 2014, 13, 476–480.

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SYNOPSIS TOC. Chao Huang, Kunyi Wang, Zhongjian Yang, Li Jiang, Renming Liu, Rongling Su, Zhang-Kai Zhou, and Xuehua Wang Up-Conversion Perovskite Nanolaser with Single Mode and Low Threshold

TOC Graphic

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Figure 1. Preparation and morphology of our samples. a, the preparation procedures of perovskite nanoplates of CsPbX3; b, the scheme of the nanostructure of perovskite lead halide nanocrystal; c, a typical SEM and TEM (the insert picture) image showing the morphology of perovskite nanoplate in low and high magnifications, respectively (the scale bar of insert is 100 nm); d, AFM measurement results of a typical single perovskite (CsPbBr2Cl) nanoplate, showing the thickness is about 150 nm; e, HRTEM and SEAD results of a single CsPbBr2Cl nanoplate, demonstrating a high crystalline quality with the lattice of 0.58 nm; f, powder XRD results further confirmed the orthorhombic phase of CsPbX3. 179x142mm (300 x 300 DPI)

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Figure 2. Optical measurements of colloidal ensemble samples in room temperature. a, a photon image of CsPbX3 (X = Br, Cl) NC solution illuminated by a hand-holding UV light, showing three different bright lights; b, the absorption and PL properties of the colloidal CsPbX3 NC solution, in which one can see the edge of absorption curve (solid) locates near the PL peak (dashed line) for each sample (sample i, ii, and iii are the same in figure a and b); c, up-conversion PL spectra of colloidal CsPbBr2Cl NCs; d, the excitation dependence on up-conversion PL of three different samples, from the fitting results of which nearly the same slope ν of ~2.05 can be found. 68x55mm (300 x 300 DPI)

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Figure 3. Single mode lasing from one single perovskite (CsPbBr2Cl) nanoplate measured at 77 K. a, the PL spectra of a nanoplate with different excitation intensities and the same incident wavelength of 780 nm, where single mode lasing at 510 nm is observed, and the insert picture is the measured nanoplate with scale bar of 200 nm; b, the excitation dependence on the up-conversion emission intensity of the single mode lasing, where a lasing threshold of 4.48 µJ/cm2 and slope of 2.03 are obtained; c, the simulated electric field distributions at the wavelength of 510 nm, demonstrating the generation of WGM in the nanoplate structure; d, the simulated emission spectrum, which agrees well with the experimental result. 71x60mm (300 x 300 DPI)

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Figure 4. Multi-mode lasing of single perovskite (CsPbBr2Cl) nanoplate measured at 77 K. a, the PL spectra of a nanoplate under different excitation fluences, showing three obvious laser modes (the scale bar is 100 nm); b, the statistic results of lasing thresholds and the nanoplate sizes of the samples with different laser modes. 158x287mm (300 x 300 DPI)

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