IntroductionRecently, halide perovskite nanomaterials have been exploited as revolutionary materials in various research fields due to their low cost, long-range charge transport, high absorption coefficient, and photoluminescence quantum yield. [1][2][3][4][5][6][7][8][9][10][11] The exploration of these materials has been motivated by their potential applications not only in solar cells but also in wide-range tunable emission sources, such as perovskite-based light emitting devices (LEDs), photodetectors, and lasing devices. [5][6][7][8][9][10][11][12][13] Since the first preparation of all-inorganic CsPbX 3 (X = Cl, Br, I) nanocrystals (NCs) with tunable bandgaps, [9] CsPbX 3 NCs have been intensively investigated for potential applications in light displays and nanolasers. [7,[9][10][11] Although all-inorganic lead halide perovskite nanomaterials can exhibit outstanding optoelectronic performance, such materials still suffer from poor stability due to a high sensitivity to moisture in the ambient environment and fluctuation of the fluorescence (blinking property), which can hinder further commercial applications. [14][15][16][17] Therefore, improving stability in an air environment is one of the most critical factor that needs to be addressed for the realization of commercially available perovskite-based optoelectronic devices. In addition, blinking, which was first discovered in CdSe quantum dots (QDs) in 1996, [18] is another critical factor limiting the further practical application of 0 D QDs. In general, the blinking effect is the random switching between a bright emission status (neutral states) and dark status due to nonradiative Auger recombination (charged states) driven by charge transfer. [19,20] The blinking phenomenon reduces the practicability of the corresponding perovskite-based optoelectronic devices. Hence, effective suppression of the fluorescence fluctuation of perovskite QDs will advance progress in the lighting and display fields.It has been generally recognized that a coating method is an effective strategy for protecting colloidal nanoparticles from moisture and improving their photostabilities, such as CdSe/ ZnS, [21] CdSe/CdS, [21] and CdTe/ZnS QDs. [22] In addition, as an attractive transparent inorganic material, the silica coating is considered to be a simpler approach to isolate QDs from the air Perovskites have emerged as a class of cutting-edge photovoltaic and lightemitting materials. However, poor stability due to high moisture sensitivity and undesirable blinking severely limits their further application. Here, to solve these problems without destroying optoelectronic performance, a simple process for the fabrication of nonblinking CsPbBr 3 quantum dots (QDs) is investigated. By embedding CsPbBr 3 QDs into waterless silica spheres, the blinking of QDs can be strikingly suppressed, with an effective improvement of the moisture resistance and enhanced photostability. The silica sphere can also prevent anion exchange of different halide elements between perovskite QDs. Ultrasta...

FETs), [10,11] memristors, [12,13] and nano lasers [14][15][16] because of their unique optical and electronic characteristics. Recently, much research has been carried on the amplified spontaneous emission (ASE) and lasing of perovskite materials because of their tunable bandgap. For examples, Xing et al. have reported lowtemperature solutionprocessed wavelengthtunable perovskites for lasing, [17] and Xiong et al. have reported nearinfrared nanolasers (Q around 1320) based on organic-inor ganic hybrid perovskite CH 3 NH 3 PbX 3 (X = Cl, Br, I) nanoplatelets. [18] However, regardless of their superior optoelectronic performance, the instability of organicinorganic hybrid perovskites due to their susceptibility for hydrolysis is recog nized as a critical issue for their further practical applications. [19][20][21] Compared to organic-inorganic hybrid perovskites, an allinorganic cesium lead halide perovskite CsPbX 3 (X = Cl, Br, I) has been developed to improve the chemical stability. [22][23][24] In the past several years, allinorganic perovskite nanomaterials CsPbX 3 (X = Cl, Br, I) have found many applications including for amplified spontaneous emission (ASE), lasing, and displays thanks to their excel lent optical performance. [25][26][27][28][29] It is well known that one and twodimensional (2D) crystals, including nanowires, [25,30] nanorods, [31] nanoplates, [30] and microplates [32] are efficient optical gain materials for optical amplification. Moreover, Halide perovskite nanomaterials have recently attracted a lot of attention in the nanoscale laser research field, especially two-photon pumped lasing in halide perovskite nanomaterials has been considered as an ideal alternative strategy to achieve frequency upconversion. However, the poor stability of current organic-inorganic lead halide perovskite materials hinder their further practical applications. Herein, facile solution-processed cesium lead halide perovskite CsPbX 3 (X = Br, I, or Cl) microcubes with low-threshold lasing, high quality, enhanced stability, and excellent wavelength tunability are reported. These as-prepared CsPbX 3 microcubes display excellent structure stability under ambient conditions for several months and they are found to be more robust than their organic-inorganic counterparts. The smooth end facets and wavelength-comparable dimensions make these microcubes promising for high-quality laser cavities in three dimensions. Fabry-Perot lasing is demonstrated in CsPbX 3 microcubes, the process of which is investigated by dynamic emission. In addition, tunable amplified spontaneous emission is achieved with low threshold under both one-and two-photon excitation, which can maintain a stable emission for over 10 hours under continuous intense laser shots in ambient atmosphere. The findings suggest that solution-processed all-inorganic perovskite microcubes can be used as excellent gain medium for frequency upconversion lasers, which would offer a new platform for nonlinear photoelectric devices.

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Zero-dimensional (0D) perovskites are emerging as a class of optoelectronic materials due to their unprecedented strong excitonic properties and high stability. Although the photoluminescence properties of 0D perovskites (Cs 4 PbX 6 ) are investigated, the origin of green emission is still opaque, and their lasing performances are not reported. Herein, using the femtosecond transient absorption measurements to study the photophysical properties of Cs 4 PbBr 6 , the presence of polarons in Cs 4 PbBr 6 is revealed, which provides the evidence that the green emission is contributed from the intrinsic behavior of Cs 4 PbBr 6 rather than CsPbBr 3 impurities. The successful lasing achieved from Cs 4 PbBr 6 microdisks (MDs) by a room-temperature reverse microemulsion method is demonstrated. The as-prepared MDs with a smooth surface and a regular geometric structure can act as ideal whispering-gallery-mode microcavities. Optically pumped single-mode lasing with a low threshold and high-quality factor is successfully achieved from MDs under both one-and two-photon excitation at room temperature. The MDs display an excellent stability while stored under ambient conditions for several months. In addition, the phase transformation between CsPbBr 3 and Cs 4 PbBr 6 can be easily achieved via tuning the amounts of surfactants. This work suggests that 0D perovskites can be promising materials toward the development of miniaturized lasers and other optoelectronic devices.

Zero‐Dimensional Perovskites In article number http://doi.wiley.com/10.1002/solr.201900127, Xiaosheng Tang, Juan Du, Yuxin Leng, and co‐workers study the photophysical properties of zero‐dimensional Cs4PbBr6 by using femtosecond transient absorption measurements; the existence of polarons provides evidence of the inherent green emission from Cs4PbBr6. Furthermore, the excellent stable lasing performance at room temperature from Cs4PbBr6 perovskite microdisks is successfully achieved.

Formamidinium (HC(NH2)+; FA) lead halide perovskites have emerged as potential candidates for solar cells, light‐emitting diodes, and lasing applications. However, the severely poor photostability of this material under UV irradiation seriously restricts the application on optoelectronic devices. In this paper, formamidinium lead halide (FAPbX3) quantum dots (QDs) adhered uniformly on the surface of amino‐mediated silica (A‐SiO2) spheres are successfully synthesized using a facile ligand‐assisted reprecipitation (LARP) method. Amazingly, the FAPbBr3/A‐SiO2 composites demonstrate excellent photostability after continuous illumination under UV lamps due to the effective suppression of the interactions and mutual contact between FAPbBr3 particles. In addition, the up‐conversion random lasing with a high quality (Q) factor of 1307 and low threshold of 413.7 µJ cm‐2 is successfully achieved from the FAPbBr3/A‐SiO2 composites at room‐temperature, which originates from the multiple random scattering of light and photon recycling provided by the silica spheres and the high gain characteristic of FAPbBr3 QDs. Moreover, different from regular lasers, random lasing does not rely on a laser cavity, which is promising in angle‐unlimited optical performance and easy/low‐cost fabrication. This work will open the window of high‐performance random lasers for digital light projector, high speed imaging, and speckle‐free full‐field imaging application.

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