Flexible Organometal-Halide Perovskite Lasers for Speckle Reduction in Imaging Projection

Speckle-Free, Angle-Free, Cavity-Free White Laser with a High Color Rendering Index

The freedom from efficiency droop motivates monochromatic lasers to progress in general lighting applications due to the demand for more efficient and sustainable light sources. Still, a white light based on monochromatic lasers with high lighting quality, such as a high color rendering ability, an angle-independent output, and a speckle-free illumination, has not yet been fabricated nor demonstrated. Random lasers, with the special mechanism caused by multiple scattering, the angle-free emission, and the uncomplicated fabrication processes, inspire us to investigate the feasibility of utilizing them in general lighting. In this work, a white random laser with a high color rendering index (CRI) value, regardless of pumping energy and observing direction, was performed and discussed. We also investigated the stability of white RL as its CIE chromaticity coordinates exhibit negligible differences with increasing pump energy density, retaining its high-CRI measurement. Also, it exhibits angle-independent emission while having a high color rendering ability. After passing through a scattering film, it generated no speckles compared to the conventional laser. We demonstrated the advances in white laser illumination, showing that a white random laser is promising to be applied for high-brightness illumination, biological-friendly lighting, accurate color selections, and medical sensing.

Unusual Spectrally Reproducible and High Q-Factor Random Lasing in Polycrystalline Tin Perovskite Films

An unusual spectrally reproducible near-IR random lasing (RL) with no fluctuation of lasing peak wavelength is disclosed in polycrystalline films of formamidinium tin triiodide perovskite, which have been chemically stabilized against Sn²⁺ to Sn⁴⁺ oxidation. Remarkably, a quality Q-factor as high as ≈10⁴ with an amplified spontaneous emission (ASE) threshold as low as 2 µJ cm^-2 (both at 20 K) are achieved. The observed spectral reproducibility is unprecedented for semiconductor thin film RL systems and cannot be explained by the strong spatial localization of lasing modes. Instead, it is suggested that the spectral stability is a result of such an unique property of Sn-based perovskites as a large inhomogeneous broadening of the emitting centers, which is a consequence of an intrinsic structural inhomogeneity of the material. Due to this, lasing can occur simultaneously in modes that are spatially strongly overlapped, as long as the spectral separation between the modes is larger than the homogeneous linewidth of the emitting centers. The discovered mechanism of RL spectral stability in semiconductor materials, possessing inhomogeneous broadening, opens up prospects for their practical use as cheap sources of narrow laser lines.

Non-resonant lasing in a deep-hole scattering cavity

Random lasers are promising in the spectral regime, wherein conventional lasers are unavailable, with advantages of low fabrication costs and applicability of diverse gain materials. However, their practical application is hindered by high threshold powers, low power efficiency, and difficulties in light collection. Here, we demonstrate a power-efficient easy-to-fabricate non-resonant laser using a deep hole on a porous gain material. The laser action in this counterintuitive cavity was enabled by non-resonant feedback from strong diffuse reflections on the inner surface. Additionally, significant enhancements in slope efficiency, threshold power, and directionality were obtained from cavities fabricated on a porous Nd:YAG ceramic.

Perovskite Random Lasers, Process and Prospects

Random lasers (RLs) are a kind of coherent light source with optical feedback based on disorder-induced multiple scattering effects instead of a specific cavity. The unique feedback mechanism makes RLs different from conventional lasers. They have the advantages of small volume, flexible shape, omnidirectional emission, etc., and have broad application prospects in the fields of laser illumination, speckle-free imaging, display, and sensing. Colloidal metal-halide perovskite nanomaterials are a hot research field in light sources. They have been considered as desired gain media owing to their superior properties, such as high photoluminescence, tunable emission wavelengths, and easy fabrication processes. In this review, we summarize the research progress of RLs based on perovskite nanomaterials. We first present the evolution of the RLs based on the perovskite quantum dots (QDs) and perovskite films. The fabrication process of perovskite nano-/microstructures and lasers is discussed in detail. After that, the frontier applications of perovskite RLs are discussed. Finally, the challenges are discussed, and the prospects for further development are proposed.

Giant Enhancement and Directional Second Harmonic Emission from Monolayer WS2 on Silicon Substrate via Fabry-Pérot Micro-Cavity

Two-dimensional transition metal dichalcogenides (TMDs) possess large second-order optical nonlinearity, making them ideal candidates for miniaturized on-chip frequency conversion devices, all-optical interconnection, and optoelectronic integration components. However, limited by subnanometer thickness, the monolayer TMD exhibits low second harmonic generation (SHG) conversion efficiency (<0.1%) and poor directionality, which hinders their practical applications. Herein, we proposed a Fabry-Pérot (F-P) cavity formed by coupling an atomically thin WS₂ film with a silicon hole matrix to enhance the SH emission. A maximum enhancement (∼1580 times) is achieved by tuning the excitation wavelength to be resonant with the microcavity modes. The giant enhancement is attributed to the strong electric field enhancement in the F-P cavity and the oscillator strength enhancement of excitons from suspended WS₂. Moreover, directional SH emission (divergence angle ∼5°) is obtained benefiting from the resonance of the F-P microcavity. Our research results can provide a practical sketch to develop both high-efficiency and directional nonlinear optical devices for silicon-based on-chip integration optics.

Amplified spontaneous emission from all-inorganic perovskite on a flexible substrate with silk fibroin

Stretchable microcavity lasers reveal potential application in flexible displays, biomedicine, and wearable devices in the near future. In this work, we investigated the characteristic of amplified spontaneous emission (ASE) from all inorganic CsPbBr₃ QDs on a flexible PET substrate with the assistance of biocompatible silk fibroin (SF) film. In comparison with the sample on PET directly, the ASE of all-inorganic perovskite film revealed a lower threshold of 32.7 μJ/cm², higher slope efficiency, and a larger gain coefficient of around 100.0 cm⁻¹ owing to the better stack and good arrangement of the CsPbBr₃ QDs on top of the SF film. For the temperature-dependent ASE measurement, the larger characteristic temperature of around 277 K is obtained from CsPbBr₃ QD/SF film, and the emission peak reveals a slight shift with temperature variation, which indicates its temperature-insensitive property. As the curvature of flexible substrate increases under the mechanical bending, the lasing threshold of CsPbBr₃ QD/SF film was reduced along with the increase in slope efficiency owing to the enhancement in the index guiding effect.

Constraint Mechanism of Power Device Design Based on Perovskite Quantum Dots Pumped by an Electron Beam

This paper studied the constraint mechanism for power device design based on perovskite quantum dots pumped by an electron beam. Combined with device designing, an experimental system of self-saturation luminescence and aging failure was designed for CsPbBr3 films. On this basis, we further completed the self-saturation luminescence and aging failure experiment and constructed a model of self-saturation luminescence and aging failure for CsPbBr3 device designing. Three constraints were proposed after analyzing and discussing the experimental data. Firstly, too high of a pumping current density makes it difficult to effectively promote the enhancement of luminescence efficiency. Secondly, radiation decomposition and aging failure of CsPbBr3 films are mainly related to the polarized degree of CsPbBr3 nanocrystals. Thirdly, by increasing the pumping electric field, the pumping energy can be effectively and widely delivered to the three-dimensional quantum dots film layer space, and there is a nonlinear relationship between the attenuation of the pumping energy density and the increment of the pumping electric field, which will effectively avoid the local high-energy density of instantaneous optical pumping.

Ultracompact Nanophotonics: Light Emission and Manipulation with Metasurfaces

Internet of Things (IoT) technology is prosperous for the betterment of human well-being. With the expeditious needs of miniature functional devices and systems for adaptive optics and light manipulation at will, relevant sensing techniques are thus in the urgent stage of development. Extensive developments in ultrathin artificial structures, namely metasurfaces, are paving the way for the next-generation devices. A bunch of tunable and reconfigurable metasurfaces with diversified catalogs of mechanisms have been developed recently, enabling dynamic light modulation on demand. On the other hand, monolithic integration of metasurfaces and light-emitting sources form ultracompact meta-devices as well as exhibiting desired functionalities. Photon-matter interaction provides revolution in more compact meta-devices, manipulating light directly at the source. This study presents an outlook on this merging paradigm for ultracompact nanophotonics with metasurfaces, also known as metaphotonics. Recent advances in the field hold great promise for the novel photonic devices with light emission and manipulation in simplicity.

Self-Powered Organometal Halide Perovskite Photodetector with Embedded Silver Nanowires

Metal-semiconductor-metal (MSM) configuration of perovskite photodetectors (PPDs) suggests easy and low-cost manufacturing. However, the basic structures of MSM PPDs include vertical and lateral configurations, which require the use of expensive materials such as transparent conductive oxides or/and sophisticated fabrication techniques such as lithography. Integrating metallic nanowire-based electrodes into the perovskite photo-absorber layer to form one-half of the MSM PPD structure could potentially resolve the key issues of both configurations. Here, a manufacturing of solution-processed and self-powered MSM PPDs with embedded silver nanowire electrodes is demonstrated. The embedding of silver nanowire electrode into the perovskite layer is achieved by treating the silver nanowire/perovskite double layer with a methylamine gas vapor. The evaporated gold layer is used as the second electrode to form MSM PPDs. The prepared MSM PPDs show a photoresponsivity of 4 × 10-5 AW-1 in the UV region and 2 × 10-5 AW-1 in the visible region. On average, the devices exhibit a photocurrent of 1.1 × 10-6 A under white light (75 mW cm-2) illumination with an ON/OFF ratio of 83.4. The results presented in this work open up a new method for development and fabrication of simple, solution-processable MSM self-powered PPDs.

Toward stable lead halide perovskite solar cells: A knob on the A/X sites components

Hybrid lead halide ABX3 perovskite solar cells (PSCs) have emerged as a strong competitor to the traditional solar cells with a certified power conversion efficiency beyond 25% and other remarkable features such as light weight, solution processability, and low manufacturing cost. Further development on the efficiency and stability brings forth increasing attention in the component regulation, such as partial or entire substitution of A/B/X sites by alternative elements with similar size. However, the relationships between composition, property, and performance are poorly understood. Here, the instability of PSCs from the photon-, moisture-, thermal-, and mechanical-induced degradation was first summarized and discussed. In addition, the component regulation from the A/X sites is highlighted from the aspects of band level alignment, charge-carrier dynamics, ion migration, crystallization behavior, residual strain, stoichiometry, and dimensionality control. Finally, the perspectives and future outlooks are highlighted to guide the rational design and practical application of PSCs.

Robust and Flexible Random Lasers Using Perovskite Quantum Dots Coated Nickel Foam for Speckle-Free Laser Imaging

The advantage of using flexible metallic structures as the substrate of flexible lasers over plastic materials is its strong mechanical strength and high thermal conductivity. Here, it is proposed to deposit CsPbBr₃ perovskite quantum dots onto Ni porous foam for the realization of flexible lasers. Under two-photon 800 nm excitation at room temperature, incoherent random lasing emission is observed at ≈537 nm. By external deformation of the Ni porous foam, incoherent random lasing can be tuned to amplified spontaneous emission as well as the corresponding lasing threshold be controlled. More importantly, it is demonstrated that the laser is robust to intensive bending (>1000 bending cycles) with minimum effect on the lasing intensity. This flexible laser is also shown to be an ideal light source to produce a "speckle" free micro-image.

Two-Dimensional Crystalline Gridding Networks of Hybrid Halide Perovskite for Random Lasing

We report fabrication of large-scale homogeneous crystallization of CH3NH3PbBr3 (MAPbBr3) in the patterned substrate by a two-dimensional (2D) grating. This achieves high-quality optotelectronic structures on local sites in the micron scales and a homogeneous thin-film device in a centimeter scale, proposing a convenient technique to overcome the challenge for producing large-area thin-film devices with high quality by spin-coating. Through matching the concentration of the MAPbBr3/DMF solutions with the periods of the patterning structures, we found an optimized size of the patterning channels for a specified solution concentration (e.g., channel width of 5 μm for a concentration of 0.14 mg/mL). Such a design is also an excellent scheme for random lasing, since the crystalline periodic networks of MAPbBr3 grids are multi-crystalline constructions, and supply strong light-scattering interfaces. Using the random lasing performance, we can also justify the crystallization qualities and reveal the responsible mechanisms. This is important for the design of large-scale optoelectronic devices based on thin-film hybrid halide perovskites.

All-Inorganic Lead Free Double Perovskite Li-Battery Anode Material Hosting High Li+ Ion Concentrations

Perovskite materials, as a multifunctional material, have been widely applied in the field of electrochemistry due to its ion migration properties. Although the lead based halide perovskite has been applied in the anode of the lithium battery, it is necessary to develop new lead-free perovskite anode materials because of its the instability and environmental unfriendliness. Herein, we develop a facile grinding method to prepare ultrahigh Li⁺ concentration doping Cs₂NaBiCl₆ powders, which are used as the anode material of the lithium battery. The assembled battery possesses a stable specific capacity of about 300 mA h g^-1 with over 99% Coulombic efficiency. Owing to their particular crystal structure with high adjustability, the double perovskite materials have promising potentials in lithium storage applications.

Perovskite random lasers: a tunable coherent light source for emerging applications

Metal halide perovskites have attracted increasing attention due to their superior optical and electrical characteristics, flexible tunability, and easy fabrication processes. Apart from their unprecedented successes in photovoltaic devices, lasing action is the latest exploitation of the optoelectronic performance of perovskites. Among the substantial body of research on the configuration design and light emission quality of perovskite lasers, the random laser is a very interesting stimulated emission phenomenon with unique optical characteristics. In this review article, we first comprehensively overview the development of perovskite-based optoelectronic devices and then focus our discussion on random lasing performance. After an introduction to the historical development of versatile random lasers and perovskite random lasers, we summarize several synthesis methods and discuss their material configurations and stability in synthesized perovskite materials. Following this, a theoretical approach is provided to explain the random lasing mechanism in metal halide perovskites. Finally, we propose future applications of perovskite random lasers, presenting conclusions as well as future challenges, such as quality stability and toxicity reduction, of perovskite materials with regard to practical applications in this promising field.

Halide Perovskite Semiconductor Lasers: Materials, Cavity Design, and Low Threshold

Solution-processable semiconductor lasers have been a long-standing challenge for next-generation displays, light sources, and communication technologies. Metal halide perovskites, which combine the advantages of inorganic and organic semiconductors, have recently emerged not only as excellent candidates for solution-processable lasers but also as potential complementary gain materials for filling the "green gap" and supplement industrial nanolasers based on classic II-VI/III-V semiconductors. Numerous perovskite lasers have been developed successfully with superior performance in terms of cost-effectiveness, low threshold, high coherence, and multicolor tunability. This mini review surveys the development, current status, and perspectives of perovskite lasers, categorized into thin film lasers, nanocrystals lasers, microlasers, and device concepts including polariton and bound-in-continuum lasers with a focus on material fundamentals, cavity design, and low-threshold devices in addition to critical issues such as mass fabrication and applications.

Investigation of random lasing from all-inorganic halide perovskite quantum dots prepared under ambient conditions

Random lasing from CsPbBr3 quantum dots (QDs) prepared by the hot injection method under ambient conditions has been investigated. The lasing characteristics and performance were related to the thickness and aggregation of the QDs film on a glass substrate. The perovskite emitted linear polarized ASE from the edge of the prepared sample as pump energy above a certain threshold, owing to the gain guiding effect. In comparison to the Q-switched Nd:YAG laser, the prepared perovskite random lasers produced a speckle reduced image with a lower contrast of around 0.051. Through temperature-dependent measurements under a surface normal emission configuration, the photon energy of ASE revealed a red shift as the temperature increased and showed a larger characteristic temperature of around 230 K. This result illustrates that the perovskite prepared under ambient conditions can be a promising material for a microcavity laser in the near future.

Inhomogeneous Trap-State-Mediated Ultrafast Photocarrier Dynamics in CsPbBr3 Microplates

Quantitatively elucidating photocarrier dynamics mediated by trap states in perovskites is crucial for establishing a structure-performance relation and understanding the interfacial photocarrier transport mechanism. Here, trap-state-mediated photocarrier dynamics in defect-rich CsPbBr₃ microplates are noninvasively investigated by ultrafast laser spectroscopy. Time-resolved photoluminescense (TRPL) measurements as a function of sample thickness indicate that trap densities of surface and bulk regions are inhomogeneous, leading to fast and slow decay components of TRPL, respectively. Fast and slow PL lifetimes present the same decreasing trend as the thickness is decreased from 5 to 0.1 μm, suggesting that both surface and bulk trap densities dramatically increase in sub-micrometer thick microplates. Furthermore, dynamical competition of ultrafast photocarrier energy relaxations between surface and bulk regions is studied in a 1.6 μm-thick sample by temporally correlating pump fluence-dependent TRPL with transient absorption signals. Strikingly, long-lived hot carriers (20 ps) are observed and complete filling of mid-gap trap states in the surface region can markedly enhance PL emission in the bulk region. By control measurements, we attribute these anomalous phenomena to the polaron-assisted ultrafast energy transfer process across the surface-bulk interface. Our results provide new insights into dynamical photocarrier energy relaxations and interfacial energy transport for inorganic perovskites.

Study of laser actions by bird's feathers with photonic crystals

Random lasers had been made by some biomaterials as light scattering materials, but natural photonic crystals have been rarely reported as scattering materials. Here we demonstrate the ability of natural photonic crystals to drive laser actions by sandwiched the feathers of the Turquoise-Fronted Amazon parrot and dye between two plastic films. Parrot feathers comprise abundant photonic crystals, and different color feathers compose of different ratios of the photonic crystal, which directly affect the feather reflectance. In this study, the multi-reflection scattering that occurred at the interface between the photonic crystal and gain media efficiently reduce the threshold; therefore, the more photonic crystal constitutes in the feathers; the lower threshold can be obtained. The random lasers can be easily made by the integration of bird feather photonic crystals and dye with a simple and sustainable manufacturing approach.

Non-resonant power-efficient directional Nd:YAG ceramic laser using a scattering cavity

Non-resonant lasers exhibit the potential for stable and consistent narrowband light sources. Furthermore, non-resonant lasers do not require well-defined optics, and thus has considerably diversified the available types of laser gain materials including powders, films, and turbid ceramics. Despite these intrinsic advantages, the practical applications of non-resonant lasers have been limited so far, mainly because of their low power efficiency and omnidirectional emission. To overcome these limitations, here we propose a light trap design for non-resonant lasers based on a spherical scattering cavity with a small entrance. Using a porous Nd³⁺:YAG ceramic, directional laser emission could be observed with significant enhancements in the slope efficiency and linewidth (down to 32 pm). A theoretical model is also developed to describe and predict the operation characteristics of proposed non-resonant laser.

Directing random lasing emission using cavity exciton-polaritons

Random lasing is an intriguing phenomenon occurring in disordered structures with optical gain in which light scattering provides the necessary feedback for lasing action. Unlike conventional lasers, random lasing systems emit in all directions due to light scattering. While this property can be desired in some cases, directional emission remains required for most applications. In a vertical microcavity containing the hybrid perovskite CH₃NH₃PbBr₃, we report here the coupling of the emission of a random laser with a cavity polaritonic resonance, resulting in a directional random lasing, whose emission angles can be tuned by varying the cavity detuning and reach values as large as 15.8^° and 22.4^°.

Room-temperature random lasing of metal-halide perovskites via morphology-controlled synthesis

Film morphology and the corresponding structural configuration can profoundly affect the optical performance, especially the random lasing action in organic-inorganic metal-halide perovskite thin films. They can be controlled in both micro- and nano-scale by manipulating different processing parameters such as the ratios of engineered solvent mixtures, spin-coating speed and backplane temperature. With the optimized parameters, the synthesized bare perovskite thin films can achieve room-temperature random lasing action with the energy pumping threshold down to 0.9 mJ cm^-2 and the corresponding β factor is estimated to be about 0.14. The bare films also show a long-time lasing reliability, maintaining lasing intensity after an optical pumping of 12 × 10⁵ pulses. Meanwhile, in the lifetime test under ambient conditions, the bare films can sustain up to 7 days without any sealing package. Moreover, the perovskite thin films can also be synthesized on flexible substrates with the total area up to 100 cm², paving a potential way for fabricating large-area and flexible random lasers in speckle-free laser projection and imaging.

Constructing Caesium-Based Lead-Free Perovskite Photodetector Enabling Self-Powered Operation with Extended Spectral Response

Since the discovery of the state-of-the-art hybrid halide perovskites, their application in optoelectronic systems has drawn considerable attention. However, the toxicity from lead (Pb) and the volatility induced by organic constituents hinder their future large-scale market development. Herein, a fully inorganic Pb-free halide perovskite based on robust Cs₃Bi₂I₉ is synthesized and realized its potential in photodetector application. The material property investigation suggests the good crystalline quality with strong absorption coefficient suitable for photodetection. An interesting feature based on the extended absorption is obtained, which is the characteristic of a weak phonon-assisted transition. Additionally, the morphological features display the beautifully grown micrometer-sized crystals of Cs₃Bi₂I₉. The fabricated photodetector demonstrated the self-powered operation (zero-bias state) with a very low dark current of 0.46 pA. Profiting from this, an improved photosensitivity of 1.4 × 10⁴ is achieved. Moreover, along with self-powered photodetection, the photodetector exhibits a broad spectral response (450-950 nm), high detectivity (1.2 × 10¹⁰/1.6 × 10¹² Jones), high responsivity (0.59 μA W^-1/3.8 mA W^-1), and fast response speed (ms) under a weak optical signal of 0.1 mW cm^-2 with a larger active area of 0.25 cm². The photodetector shows high photostability which was well retained for almost 2000 repetitive cycles without degradation. More strikingly, based on the core stability of the perovskite film, an excellent long-term stability of 3 months (90 days) is achieved for the photodetector even after exposure to moist air (75% relative humidity). This study thus highlights one of the few Pb-free all-inorganic perovskite photodetectors employing a simple device architecture with a larger active area that outshines by showing efficient and comparable performance under the self-powered mode under low light conditions.

Naturally Degradable Photonic Devices with Transient Function by Heterostructured Waxy-Sublimating and Water-Soluble Materials

Combined dry-wet transient materials and devices are introduced, which are based on water-dissolvable dye-doped polymers layered onto nonpolar cyclic hydrocarbon sublimating substrates. Light-emitting heterostructures showing amplified spontaneous emission are obtained on transient elements and used as illumination sources for speckle-free, full-field imaging, and transient optical labels are realized that incorporate QR-codes with stably encoded information. The transient behavior is also studied at the microscopic scale, highlighting the real-time evolution of material domains in the sublimating compound. Finally, the exhausted components are fully soluble in water thus being naturally degradable. This technology opens new and versatile routes for environmental sensing, storage conditions monitoring, and organic photonics.

Random lasing in cesium lead iodide (CsPbI3) thin films with no surface passivation

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.

Nano-Micro Dimensional Structures of Fiber-Shaped Luminous Halide Perovskite Composites for Photonic and Optoelectronic Applications

Perovskite nanomaterials have been revealed as highly luminescent structures regarding their dimensional confinement. In particular, their promising potential lies behind remarkable luminescent properties, including color tunability, high photoluminescence quantum yield, and the narrow emission band of halide perovskite (HP) nanostructures for optoelectronic and photonic applications such as lightning and displaying operations. However, HP nanomaterials possess such drawbacks, including oxygen, moisture, temperature, or UV lights, which limit their practical applications. Recently, HP-containing polymer composite fibers have gained much attention owing to the spatial distribution and alignment of HPs with high mechanical strength and ambient stability in addition to their remarkable optical properties comparable to that of nanocrystals. In this review, the fabrication methods for preparing nano-microdimensional HP composite fiber structures are described. Various advantages of the luminescent composite nanofibers are also described, followed by their applications for photonic and optoelectronic devices including sensors, polarizers, waveguides, lasers, light-down converters, light-emitting diode operations, etc. Finally, future directions and remaining challenges of HP-based nanofibers are presented.

Effect of Passivation Layer on the Thin Film Perovskite Random Lasers

Novel functionalities of disorder-induced scattering effect in random lasers, attributed to low spatial coherence, draw remarkable attention in high-contrast to superior quality speckle-free imaging applications. This paper demonstrates perovskite-polystyrene (PS)-based random lasing action with robust optical performance at room temperature. Optical characterizations are carried out upon perovskite thin films addition with polystyrene of different mixing concentrations (wt.%). A low threshold lasing operation is achieved with an increasing concentration of polystyrene, accompanying a wavy surface texture with high surface roughness. The rough surface dominating multiple scattering effects leads to enhanced feedback efficiency. Moreover, this study also elucidates efficient fabrication process steps for the development of high quality and durable PS-based random lasers. With the advantages of reduced coherent artifacts and low spatial coherence, speckle free projection images of the USAF (U. S. Air Force MIL-STD-150A standard of 1951) resolution test chart are shown for different PS-based random lasers.

Two-Step Patterning of Scalable All-Inorganic Halide Perovskite Arrays

Halide perovskites have many important optoelectronic properties, including high emission efficiency, high absorption coefficients, color purity, and tunable emission wavelength, which makes these materials promising for optoelectronic applications. However, the inability to precisely control large-scale patterned growth of halide perovskites limits their potential toward various device applications. Here, we report a patterning method for the growth of a cesium lead halide perovskite single crystal array. Our approach consists of two steps: (1) cesium halide salt arrays patterning and (2) chemical vapor transport process to convert salt arrays into single crystal perovskite arrays. Characterizations including energy-dispersive X-ray spectroscopy and photoluminescence have been employed to confirm the chemical compositions and the optical properties of the as-synthesized perovskite arrays. This patterning method enables the patterning of single crystal cesium lead halide perovskite arrays with tunable spacing (from 2 to 20 μm) and crystal size (from 200 nm to 1.2 μm) in high production yield (almost every pixel in the array is successfully grown with converted perovskite crystals). Our large-scale patterning method renders a platform for the study of fundamental properties and opportunities for perovskite-based optoelectronic applications.

Dynamically wavelength-tunable random lasers based on metal-organic framework particles

We propose a strategy to construct dynamically tunable random lasers by continuously adjusting the excited state of gain molecules spatially confined in the nanoporous channels of metal-organic framework particles. Wavelength-tunable random lasers are achieved by thermally manipulating the intramolecular charge transfer process of gain molecules. The wavelength-tunable response to thermal stimuli exhibits excellent reversible behavior. We envisage that such random lasers based on metal-organic frameworks will raise new fundamental issues regarding light-matter interactions in complex photonic media and open up a new avenue toward highly efficient light-emitting devices.

Materials chemistry and engineering in metal halide perovskite lasers

The invention and development of the laser have revolutionized science, technology, and industry. Metal halide perovskites are an emerging class of semiconductors holding promising potential in further advancing the laser technology. In this Review, we provide a comprehensive overview of metal halide perovskite lasers from the viewpoint of materials chemistry and engineering. After an introduction to the materials chemistry and physics of metal halide perovskites, we present diverse optical cavities for perovskite lasers. We then comprehensively discuss various perovskite lasers with particular functionalities, including tunable lasers, multicolor lasers, continuous-wave lasers, single-mode lasers, subwavelength lasers, random lasers, polariton lasers, and laser arrays. Following this a description of the strategies for improving the stability and reducing the toxicity of metal halide perovskite lasers is provided. Finally, future research directions and challenges toward practical technology applications of perovskite lasers are provided to give an outlook on this emerging field.

In-plane stimulated emission of polycrystalline CH3NH3PbBr3 perovskite thin films

Hybrid organic–inorganic lead halide perovskites have been investigated extensively within the last decades, for its great potential in efficient solar cells and as an ideal light source. Among the studies on stimulated emission (SE), the emission is either out-of-plane for polycrystalline films or in-plane with randomly aligned single microcrystals and nanowires. In this work, we revealed in-plane propagation of SE from bromine-based perovskite polycrystalline thin films (CH₃NH₃PbBr₃, or MAPbBr₃). The output from in-plane SE is an order higher than the out-of-plane emission. It is proposed that large crystalline flakes in the films lead to the in-plane lasing phenomena. The output coupling can be found at grain boundaries, intergrain gaps, and artificial structures. Simulative results support the experimental phenomenon that large crystalline grains are profitable for in-plane propagation and over 90% photons can be sufficiently outcoupled when the gap is larger than a micron. Considering the fabrication and handling convenience, we propose that the MAPbBr₃ thin films can be easily integrated for in-plane applications as the light source for photonic chips etc.

MAPbBr₃ perovskite thin film contains large crystal flakes, which support the in-plane stimulated emission and its propagation within these polycrystalline films. The emission scatters at the natural or artificial edge of the film.

Surface-Emitting Perovskite Random Lasers for Speckle-Free Imaging

Random lasers have been ideal illumination sources for speckle-free and high-speed imaging. Despite their successes, the real applications of random lasers are facing a long-standing challenge, i.e., the cumbersome size of the illuminating system. Herein, we demonstrate perovskite-based surface emitting random lasers (SERLs) and explore their applications in speckle-free imaging. The random lasers are generated by multiple scattering in a perovskite polycrystalline film sandwiched by two distributed Bragg reflectors. Owing to the tight confinement in vertical direction and large number of random resonances, the wavevectors of random lasers are dominated by their vertical components, and thus, multimode SERLs with a divergence angle of ∼3-5° and low spatial coherence are produced. By directly illuminating the patterns with the SERLs, the notable speckle noises of conventional optical images have been dramatically suppressed. This research shall provide a strategy toward the integrated spectral-free imaging systems.