Two-Dimensional Electron-Hole Plasma in Colloidal Quantum Shells Enables Integrated Lasing Continuously Tunable in the Red Spectrum

Combining integrated optical platforms with solution-processable materials offers a clear path toward miniaturized and robust light sources, including lasers. A limiting aspect for red-emitting materials remains the drop in efficiency at high excitation density due to non-radiative quenching pathways, such as Auger recombination. Next to this, lasers based on such materials remain ill characterized, leaving questions about their ultimate performance. Here, we show that colloidal quantum shells (QSs) offer a viable solution for a processable material platform to circumvent these issues. We first show that optical gain in QSs is mediated by a 2D plasma state of unbound electron-hole pairs, opposed to bound excitons, which gives rise to broad-band and sizable gain across the full red spectrum with record gain lifetimes and a low threshold. Moreover, at high excitation density, the emission efficiency of the plasma state does not quench, a feat we can attribute to an increased radiative recombination rate. Finally, QSs are integrated on a silicon nitride platform, enabling high spectral contrast, surface emitting, and TE-polarized lasers with ultranarrow beam divergence across the entire red spectrum from a small surface area. Our results indicate QS materials are an excellent materials platform to realize highly performant and compact on-chip light sources.

Green Light from Red-Emitting Nanocrystals: Broadband, Low-Threshold Lasing from Colloidal Quantum Shells in Optical Nanocavities

Spherical semiconductor nanoplatelets, known as quantum shells (QSs), have captured significant interest for their strong suppression of Auger recombination, which leads to long multiexciton lifetimes and wide optical gain bandwidth. Yet, the realization of benefits associated with the multiexciton lasing regime using a suitably designed photonic cavity remains elusive. Here, we demonstrate broadly tunable lasing from close-packed films of CdS/CdSe/CdS QSs deposited over nanopillar arrays on Si substrates. Wide spectral tuning of the stimulated emission in QSs with a fixed bandgap value was achieved by engaging single exciton (λX ∼ 634 nm), biexciton (λBX ∼ 627 nm), and multiple exciton (λMX ∼ 615-565 nm) transitions. The ensemble-averaged gain threshold of ∼ 2.6 electron-hole pairs per QS particle and the low photonic cavity fluence threshold of ∼4 μJ/cm2 were attributed to Auger suppression. The tuning of the lasing emission closely aligns with our model predictions achieved by varying the array period while preserving mode confinement and quality (Q) factors. These results mark a notable step toward the development of colloidal nanocrystal lasers.

Unidirectional Lasing from Mirror-Coupled Dielectric Lattices

This paper reports how a hybrid system composed of transparent dielectric lattices over a metal mirror can produce high-quality lattice resonances for unidirectional lasing. The enhanced electromagnetic fields are concentrated in the cladding of the periodic dielectric structures and away from the metal. Based on a mirror-image model, we reveal that such high-quality lattice resonances are governed by bound states in the continuum resulting from destructive interference. Using hexagonal arrays of titanium dioxide nanoparticles on a silica-coated silver mirror, we observed lattice resonances with quality factors of up to 2750 in the visible regime. With the lattice resonances as optical feedback and dye solution as the gain medium, we demonstrated unidirectional lasing under optical pumping, where the array size was down to 100 μm × 100 μm. Our scheme can be extended to other spectral regimes to simultaneously achieve strongly enhanced surface fields and high quality factors.

Engineering of Solid-State Nanoporous Laser through Dendrimer-Encapsulated Fluorophores

Dendrimers─nanosized macromolecules that can function as hosts for encapsulation of guest molecules─provide new avenues to engineer gain media for lasing systems. In this context, this study investigates the interplay between the geometric features of a model porous scattering medium, nanoporous anodic alumina (NAA), and the chemical features of a model fluorophore-dendrimer encapsulation system to maximize random lasing. The inner surface of the NAA platforms is functionalized with fluorophore molecules encapsulated within dendrimers via an electrostatic interaction. The resulting solid-state composite structures emit well-resolved, intense random lasing when subjected to optical pumping. By engineering fluorophore-dendrimer and geometric features of scattering medium, we can precisely tune the characteristics of random lasing emissions. It is found that lasing structures with low porosity and thickness functionalized with fluorophore molecules encapsulated in second-generation dendrimers provide the best platforms for lasing generation, resulting in a strongly polarized laser at ∼594 nm that has a high quality-gain product of ∼1588 au, a polarization quality of ∼0.86, and a lasing threshold of ∼0.05 mJ pulse-1. Comparative analysis indicates that dendrimers achieve 2.5 times better random lasing than conventional surfactants due to improved encapsulation and minimization of photobleaching. Our results reveal the importance of the fluorophore encapsulation method and design of scattering media in the engineering of random lasing platforms for applications in optical and optoelectrical systems.

High-Performance Multiwavelength GaNAs Single Nanowire Lasers

In this study, we report a significant enhancement in the performance of GaNAs-based single nanowire lasers through optimization of growth conditions, leading to a lower lasing threshold and higher operation temperatures. Our analysis reveals that these improvements in the laser performance can be attributed to a decrease in the density of localized states within the material. Furthermore, we demonstrate that owing to their excellent nonlinear optical properties, these nanowires support self-frequency conversion of the stimulated emission through second harmonic generation (SHG) and sum-frequency generation (SFG), providing coherent light emission in the cyan-green range. Mode-specific differences in the self-conversion efficiency are revealed and explained by differences in the light extraction efficiency of the converted light caused by the electric field distribution of the fundamental modes. Our work, therefore, facilitates the design and development of multiwavelength coherent light generation and higher-temperature operation of GaNAs nanowire lasers, which will be useful in the fields of optical communications, sensing, and nanophotonics.

Cavity Lasing Characteristics of Thioflavin T and Thioflavin X in Different Solvents and Their Interaction with DNA for the Controlled Reduction of a Light Amplification Threshold in Solid-State Biofilms

The lasing characteristics of Thioflavin T (ThT) and Thioflavin X (ThX) dyes were investigated in solvents with increasing viscosity: water, ethanol, butanol, ethylene glycol, and glycerol and three forms of DNA (double-helix natural, fragmented, and aggregated). The results identified that lasing thresholds and photostability depend on three critical factors: the solvation shell surrounding dye molecules, the organization of their dipole moments, which is driven by the DNA structure, and the molecules diffusion coefficient in the excitation focal spot. The research highlights that dye doped to DNA accumulated in binding sites fosters long-range dye orientation, facilitating a marked reduction of lasing thresholds in the liquid phase as well as amplified spontaneous emission (ASE) thresholds in the solid state. Leveraging insights from lasing characteristics obtained in liquid, ASE in the solid state was optimized in a controlled way by changing the parameters influencing the DNA structure, i.e., magnesium salt addition, heating, and sonication. The modifications led to a large decrease in the ASE thresholds in the dye-doped DNA films. It was shown that the examination of lasing in cavities can be useful for preparing optical materials with improved architectures and functionalities for solid-state lasers.

Quasi-Random Multimetallic Nanoparticle Arrays

This paper describes a nanofabrication procedure that can generate multiscale substrates with quasi-random microregions of nanoparticle arrays having different periodicities and metals. We combine cycles of large-area nanoparticle array fabrication with solvent-assisted wrinkle lithography to mask and etch quasi-random areas of prefabricated nanoparticles to control the fill factors of the arrays. The approach is highly flexible, and parameters, including nanoparticle size and material, array geometry, and fill factor, can be tailored independently. Multimetallic nanoparticle arrays can support surface lattice resonances at fill factors as low as 20% and can function as nanoscale cavities for lasing action with as few as 10% of the nanoparticles in an array. We demonstrated that multimetallic nanoparticle substrates that combine two or three arrays with different periodicities can exhibit lasing responses over visible and near-infrared wavelengths. Our work showcases the robust optical responses of multimetallic and periodic devices for broadband light manipulation.

Ultrasmall InGa(As)P Dielectric and Plasmonic Nanolasers

Nanolasers have great potential for both on-chip light sources and optical barcoding particles. We demonstrate ultrasmall InGaP and InGaAsP disk lasers with diameters down to 360 nm (198 nm in height) in the red spectral range. Optically pumped, room-temperature, single-mode lasing was achieved from both disk-on-pillar and isolated particles. When isolated disks were placed on gold, plasmon polariton lasing was obtained with Purcell-enhanced stimulated emission. UV lithography and plasma ashing enabled wafer-scale fabrication of nanodisks with an intended random size variation. Silica-coated nanodisk particles generated stable subnanometer spectra from within biological cells across an 80 nm bandwidth from 635 to 715 nm.

Ultrafast Antisolvent Growth of Single-Crystal CsPbBr3 Microcavity for Whispering-Gallery-Mode Lasing

In recent years, all-inorganic cesium lead bromide (CsPbBr₃) perovskites have garnered considerable attention for their prospective applications in green photonics and optoelectronic devices. However, the development of efficient and economical methods to obtain high-quality micron-sized single-crystalline CsPbBr₃ microplatelets (MPs) has become a challenge. Here, we report the synthesis of CsPbBr₃ MPs on Si/SiO₂ substrate by optimizing the ultrafast antisolvent method (FAS). This technique is able to produce well-dispersed, uniformly sized, and morphologically regular tetragonal phase single crystals, which can give strong green emission at room temperature, with excellent stability and excitonic character. Moreover, the crystals demonstrated lasing with a whispering gallery mode with a low threshold. These results suggest that the single-crystalline CsPbBr₃ MPs synthesized by this method are of high optical quality, holding vast potential for future applications in photonic devices.

Continuous-wave pumped perovskite lasers with device area below 1 μm2

Continuous-wave (CW) pumped lasers with device areas below 1 μm² constitute a key step to meeting the energy efficiency requirement for on-chip optical communications. However, a debate about whether a submicron device size and low threshold can be simultaneously satisfied has persisted owing to insurmountable radiation losses when approaching the optical diffraction limit. Herein, we demonstrate a record-small CW optically pumped perovskite laser with a device area of 0.65 μm² . We find the thresholds of submicron lasers can be lower than those of several-micron counterparts, and ascribe it to the enlarged group refractive index and modal confinement resulting from the enhanced exciton-photon coupling. Moreover, the operation temperature is elevated to 150 K through the reduction in heat generation. Our findings unveil the potential of exciton-polaritons in laser miniaturization, providing an alternative for developing low-threshold semiconductor lasers without artificial optical cavities, to approach the optical diffraction limit. This article is protected by copyright. All rights reserved.

Amplified Spontaneous Emission and Lasing from Zn-Processed AgIn5S8 Core/Shell Quantum Dots

I-III-VI ternary quantum dots (QDs) have emerged as favorable alternatives to the toxic II-VI QDs for optoelectronic and biological applications. However, their use as optical gain media for microlasers is still limited by a low fluorescence efficiency. Here, we demonstrate amplified spontaneous emission (ASE) and lasing from colloidal QDs of Zn-processed AgIn₅S₈ (AIS) for the first time. The passivation treatment on the AIS QDs yields a 3.4-fold enhancement of fluorescence quantum efficiency and a 30% increase in the two-photon absorption cross section. ASE is achieved from the AIS/ZnS core/shell QD films under both one- and two-photon pumping with a threshold fluence of ∼84.5 μJ/cm² and 3.1 mJ/cm², respectively. These thresholds are comparable to the best optical gain performance of Cd based-QDs reported in the literature. Moreover, we demonstrate a facile whispering-gallery-mode microlaser of the core/shell QDs with a lasing threshold of ∼233 μJ/cm². The passivated AIS QDs can be promising optical gain media for photonic applications.

2D Material Infrared Photonics and Plasmonics

Two-dimensional (2D) materials including graphene, transition metal dichalcogenides, black phosphorus, MXenes, and semimetals have attracted extensive and widespread interest over the past years for their many intriguing properties and phenomena, underlying physics, and great potential for applications. The vast library of 2D materials and their heterostructures provides a diverse range of electrical, photonic, mechanical, and chemical properties with boundless opportunities for photonics and plasmonic devices. The infrared (IR) regime, with wavelengths across 0.78 μm to 1000 μm, has particular technological significance in industrial, military, commercial, and medical settings while facing challenges especially in the limit of materials. Here, we present a comprehensive review of the varied approaches taken to leverage the properties of the 2D materials for IR applications in photodetection and sensing, light emission and modulation, surface plasmon and phonon polaritons, non-linear optics, and Smith-Purcell radiation, among others. The strategies examined include the growth and processing of 2D materials, the use of various 2D materials like semiconductors, semimetals, Weyl-semimetals and 2D heterostructures or mixed-dimensional hybrid structures, and the engineering of light-matter interactions through nanophotonics, metasurfaces, and 2D polaritons. Finally, we give an outlook on the challenges in realizing high-performance and ambient-stable devices and the prospects for future research and large-scale commercial applications.

Optically Excited Lasing in a Cavity-Based, High-Current-Density Quantum Dot Electroluminescent Device

Laser diodes based on solution-processable materials can benefit numerous technologies including integrated electronics and photonics, telecommunications, and medical diagnostics. An attractive system for implementing these devices is colloidal semiconductor quantum dots (QDs). The progress towards a QD laser diode has been hampered by rapid nonradiative Auger decay of optical-gain-active multicarrier states, fast device degradation at high current densities required for laser action, and unfavorable competition between optical gain and optical losses in a multicomponent device stack. Here we resolve some of these challenges and demonstrate optically excited lasing from fully functional high-current density electroluminescent (EL) devices with an integrated optical resonator. This advance has become possible due to excellent optical gain properties of continuously graded QDs and a refined device architecture, which allows for highly efficient light amplification in a thin, EL-active QD layer.

Frequency Stabilization and Optically Tunable Lasing in Colloidal Quantum Dot Superparticles

Self-assembled superparticles composed of colloidal quantum dots establish microsphere cavities that support optically pumped lasing from whispering gallery modes. Here, we report on the time- and excitation fluence-dependent lasing properties of CdSe/CdS quantum dot superparticles. Spectra collected under constant photoexcitation reveal that the lasing modes are not temporally stable but instead blue-shift by more than 30 meV over 15 min. To counter this effect, we establish a high-fluence light-soaking protocol that reduces this blue-shift by more than an order of magnitude to 1.7 ± 0.5 meV, with champion superparticles displaying mode blue-shifts of <0.5 meV. Increasing the pump fluence allows for optically controlled, reversible, color-tunable red-to-green lasing. Combining these two paradigms suggests that quantum dot superparticles could serve in applications as low-cost, robust, solution-processable, tunable microlasers.

Lanthanide-Doped Upconversion Nanoparticles: Exploring A Treasure Trove of NIR-Mediated Emerging Applications

Lanthanide-doped upconversion nanoparticles (UCNPs) possess the remarkable ability to convert multiple near-infrared (NIR) photons into higher energy ultraviolet-visible (UV-vis) photons, making them a prime candidate for several advanced applications within the realm of nanotechnology. Compared to traditional organic fluorophores and quantum dots (QDs), UCNPs possess narrower emission bands (fwhm of 10-50 nm), large anti-Stokes shifts, low toxicity, high chemical stability, and resistance to photobleaching and blinking. In addition, unlike UV-vis excitation, NIR excitation is nondestructive at lower power intensities and has high tissue penetration depths (up to 2 mm) with low autofluorescence and scattering. Together, these properties make UCNPs exceedingly favored for advanced bioanalytical and theranostic applications, where these systems have been well-explored. UCNPs are also well-suited for bioimaging, optically modulating chemistries, forensic science, and other state-of-the-art research applications. In this review, an up-to-date account of emerging applications in UCNP research, beyond bioanalytical and theranostics, are presented including optogenetics, super-resolution imaging, encoded barcodes, fingerprinting, NIR vision, UCNP-assisted photochemical manipulations, optical tweezers, 3D printing, lasing, NIR-II imaging, UCNP-molecule nanohybrids, and UCNP-based persistent luminescent nanocrystals.

Lasing in Two-Dimensional Tin Perovskites

Two-dimensional (2D) perovskites have been proposed as materials capable of improving the stability and surpassing the radiative recombination efficiency of three-dimensional perovskites. However, their luminescent properties have often fallen short of what has been expected. In fact, despite attracting considerable attention for photonic applications during the last two decades, lasing in 2D perovskites remains unclear and under debate. Here, we were able to improve the optical gain properties of 2D perovskite and achieve optically pumped lasing. We show that the choice of the spacer cation affects the defectivity and photostability of the perovskite, which in turn influences its optical gain. Based on our synthetic strategy, we obtain PEA₂SnI₄ films with high crystallinity and favorable optical properties, resulting in amplified spontaneous emission (ASE) with a low threshold (30 μJ/cm²), a high optical gain above 4000 cm^-1 at 77 K, and ASE operation up to room temperature.

Room Temperature Lasing from Semiconducting Single-Walled Carbon Nanotubes

Miniaturized near-infrared semiconductor lasers that are able to generate coherent light with low energy consumption have widespread applications in fields such as optical interconnects, neuromorphic computing, and deep-tissue optogenetics. With optical transitions at near-infrared wavelengths, diameter-tunable electronic structures, and superlative optoelectronic properties, semiconducting single-walled carbon nanotubes (SWCNTs) are promising candidates for nanolaser applications. However, despite significant efforts in this direction and recent progress toward enhancing spontaneous emission from SWCNTs through Purcell effects, SWCNT-based excitonic lasers have not yet been demonstrated. Leveraging an optimized cavity-emitter integration scheme enabled by a self-assembly process, here we couple SWCNT emission to the whispering gallery modes supported by polymer microspheres, resulting in room temperature excitonic lasing with an average lasing threshold of 4.5 kW/cm². The high photostability of SWCNTs allows stable lasing for prolonged duration with minimal degradation. This experimental realization of excitonic lasing from SWCNTs, combined with their versatile electronic and optical properties that can be further controlled by chemical modification, offers far-reaching opportunities for tunable near-infrared nanolasers that are applicable for optical signal processing, in vivo biosensing, and optoelectronic devices.

Comparative Evaluation of Penetrative and Adaptive Properties of Unfilled and Filled Resin-Based Sealants When Placed using Conventional acid Etching, Lasing, and Fissurotomy Bur Technique of Enamel Preparation: An in vitro Scanning Electron Microscope Study

Background

There is a confusion regarding selection of unfilled or filled sealant and method of enamel preparation before sealant application. This study was carried out to compare three techniques of enamel preparation using both unfilled and filled type of sealants.

Objective

The objective of the study is to assess the penetrative and adaptive ability of filled and unfilled sealants in three techniques of enamel fissure preparations.

Materials and Methods

Total 36 extracted teeth were divided into 3 groups, each containing 12 samples. The samples of Group A were prepared by conventional acid etching with 37% phosphoric acid, and the Group B was subjected to Er: YAG lasing, while in Group C, fissurotomy followed by acid etching was done. The sealant placement was carried out using split tooth design in all the samples. Assessment of penetration and adaptation was done under scanning electron microscope using the scoring criteria adopted by Kane B et al. and Dukic W et al.

Results

Group A and Group C showed better adaptation than Group B. Statistically, no significant difference was observed in the penetration property among three techniques. Similarly, the unfilled and filled sealant showed statistically nonsignificant results for the penetration and adaptation comparison.

Conclusion

Irrespective of the sealant material selected, the conventional method of acid etching alone or in conjunction with fissurotomy bur for better retentiveness seems to be an acceptable choice of treatment modality. The study will help the clinicians to choose the sealant material and technique of enamel preparation.

Threshold conditions for transversal modes of tunable plasmonic nanolasers shaped as single and twin graphene-covered circular quantum wires

We implement the lasing eigenvalue problem (LEP) approach to study the electromagnetic field in the presence of a circular quantum wire (QW) made of a gain material and wrapped in graphene cover and a dimer of two identical graphene-covered QWs, at the threshold of stationary emission. LEP delivers the mode-specific eigenvalue pairs, namely the frequencies and the threshold values of the QW gain index for the plasmon and the wire modes of such nanolasers. In our analysis, we use quantum Kubo formalism for the graphene conductivity and classical Maxwell boundary-value problem for the field functions. The technique involves the resistive boundary conditions, the separation of variables in the local coordinates, and, for the dimer, the addition theorem for the cylindrical functions. For single-wire plasmonic laser, we derive approximate engineering expressions for the lasing frequencies and threshold values of the gain index that complement the full-wave computations. For the dimer, we derive separate determinantal equations for four different classes of symmetry of the lasing supermodes and solve them numerically. Our investigation of the mode frequencies and thresholds versus the graphene and QW parameters shows that plasmon modes or, for the dimer, plasmon supermodes have lower frequencies and thresholds than the wire modes provided that the QW radius is smaller than 10μm, however in thicker wires they are comparable. Only the plasmon-mode characteristics are well-tunable using the graphene chemical potential. In the dimer, all lasing supermodes form closely located quartets, however, they quickly approach the single-wire case if the inter-wire separation becomes comparable to the radius. These results open a way for building essentially single-mode plasmonic nanolasers and their arrays and suggest certain engineering rules for their design.

Two-Photon Lasing from Two-Dimensional Homologous Ruddlesden-Popper Perovskite with Giant Nonlinear Absorption and Natural Microcavities

Two-dimensional Ruddlesden-Popper perovskites (RPPs) with multiple quantum well-like structures, strong excitonic quantum confinement, and high stability are promising optical gain media. However, the lasing from such material with a small number of inorganic well layers is difficult to achieve. Herein, we demonstrate the low-threshold upconversion lasing from the homologous RPP (PEA)₂(MA)_n-1Pb_nI_3n+1 (n = 2 and 3) microflakes with wavelength varies from 598 to 637 nm under 800 nm laser excitation at low temperature (≤153 K). Using the micro Z-scan technique, we discovered that the RPP flakes have a giant two-photon absorption coefficient β as high as 3.6 × 10³ cm GW^-1, resulting in the effective upconversion transition under two-photon excitation. Furthermore, the self-formation of Fabry-Pérot microcavities provides the support for lasing emission from the n ≥ 2 RPP flakes. Calculation results and microscopic transient absorption measurements reveal that low-threshold lasing is due to the high differential gain coefficient and the suppressed nonradiative Auger recombination rate inside the quantum confinement structures. These properties enable RPPs as potential gain media for developing upconversion microcavity lasers.

Quasi-BIC Mode Lasing in a Quadrumer Plasmonic Lattice

Plasmonic lattices of metal nanoparticles have emerged as an effective platform for strong light-matter coupling, lasing, and Bose-Einstein condensation. However, the full potential of complex unit cell structures has not been exploited. On the other hand, bound states in continuum (BICs) have attracted attention, as they provide topologically protected optical modes with diverging quality factors. Here, we show that quadrumer nanoparticle lattices enable lasing in a quasi-BIC mode with a highly out-of-plane character. By combining theory with polarization-resolved measurements of the emission, we show that the lasing mode has a topological charge. Our analysis reveals that the mode is primarily polarized out-of-plane as a result of the quadrumer structure. The quality factors of the out-of-plane BIC modes of the quadrumer array can be exceedingly high. Our results unveil the power of complex multiparticle unit cells in creating topologically protected high-Q modes in periodic nanostructures.

Direct-Bandgap Bilayer WSe2 /Microsphere Monolithic Cavity for Low-Threshold Lasing

Monolayer transition metal dichalcogenides (TMDs) have emerged as widely accepted 2D gain materials in the field of light sources owing to their direct bandgap and high photoluminescence quantum yield. However, the monolayer medium suffers from weak emission because only a single layer of molecules can absorb the pump energy. Moreover, the material degradation when transferring these fragile materials hinders their cooperation with the optical cavity further. In this study, for the first time, a high-quality monolithic structure is developed by directly growing single-domain tungsten diselenide (WSe₂ ) bilayers on single silica microsphere (MS) cavities. Such a completely wrapped structure guides the indirect-to-direct bandgap transition of WSe₂ bilayers, leading to a significantly improved photoluminescence intensity by about 60-fold. Moreover, the high-quality monolithic structure enhances the confinement factor of the cavity by more than 20-fold. Based on the above advantages, a bilayer WSe₂ /MS microlaser is realized with an ultralow threshold of 0.72 W cm^-2 , nearly an order of magnitude lower than the existing records. The results demonstrate the possibility of using multilayer TMD materials as 2D gain media and provide insights into a new ultracompact monolithic platform of TMD material/cavity for lasing devices.

Highly Tunable Enhancement and Switching of Nonlinear Emission from All-Inorganic Lead Halide Perovskites via Electric Field

Herein, we demonstrate a highly tunable enhancement and switching of nonlinear emission from all-inorganic metal halide perovskites based on an asymmetrically biased metal-insulator-semiconductor (MIS) structure. We achieve 2 orders of magnitude enhancement of the two-photon-pumped photoluminescence (TPL) from CsPbBr₃ microplates with the MIS structure, due to comprehensive effects including localized field effect, trap-filling effect, and collection enhancement. In particular, taking advantage of electric-field-induced passivation/activation of Br vacancies, we realize highly tunable TPL enhancement, ranging from ∼61.2-fold to ∼370.3-fold. Moreover, we demonstrate an efficient modulation of the two-photon-pumped lasing from the MIS structure, which exhibits electric field induced switching with a high on/off ratio of 67:1. This work has opened new avenues for steering carrier transport and nonlinear emission in lead halide perovskites, which shows great promise for realizing high-efficiency and tunable nonlinear nanophotonic devices.

Bound State in the Continuum in Nanoantenna-Coupled Slab Waveguide Enables Low-Threshold Quantum-Dot Lasing

Colloidal quantum dots (CQDs) are a promising gain material for solution-processed, wavelength-tunable lasers, with potential application in displays, communications, and biomedical devices. In this work, we combine a CQD film with an array of nanoantennas, made of titanium dioxide cylinders, to achieve lasing via bound states in the continuum (BICs). Here, the BICs are symmetry-protected cavity modes with giant quality factors, arising from slab waveguide modes in the planar CQD film, coupled to the periodic nanoantenna array. We engineer the thickness of the CQD film and size of the nanoantennas to achieve a BIC with good spatial and spectral overlap with the CQDs, based on a second-order transverse-electric (TE)-polarized waveguide mode. We obtain room-temperature lasing with a low threshold of approximately 11 kW/cm² (peak intensity) under 5-ns-pulsed optical excitation. This work sheds light on the optical modes in solution-processed, distributed-feedback lasers and highlights BICs as effective, versatile, surface-emitting lasing modes.

Multimode Robust Lasing in a Dye-Doped Polymer Layer Embedded in a Wedge-Shaped Cholesteric

Cholesteric liquid crystals (CLCs) with induced defects are one of the most prominent materials to realize compact, low-threshold and tunable coherent light sources. In this context, the investigation of optical properties of induced defect modes in such CLCs is of great interest. In particular, many studies have been devoted to the spectral control of the defect modes depending on their thickness, optical properties, distribution along the CLC, etc. In this paper, we investigate the lasing possibilities of a dye-doped polymer layer embedded in a wedge-shaped CLC. We show that multimode laser generation is possible due to the observed multiple defect modes in the PBG that enlarges the application range of the system. Furthermore, our simulations based on a Berreman 4 × 4 matrix approach for a wide range of CLC thickness show both periodic and continuous generation of defect modes along particular spectral lines inside the PBG. Such a robust spectral behaviour of induced defect modes is unique, and, to our knowledge, is not observed in similar CLC-based structures.

Quantum Dot Self-Assembly Enables Low-Threshold Lasing

Perovskite quantum dots (QDs) are of interest for solution-processed lasers; however, their short Auger lifetime has limited lasing operation principally to the femtosecond temporal regime the photoexcitation levels to achieve optical gain threshold are up to two orders of magnitude higher in the nanosecond regime than in the femtosecond. Here the authors report QD superlattices in which the gain medium facilitates excitonic delocalization to decrease Auger recombination and in which the macroscopic dimensions of the structures provide the optical feedback required for lasing. The authors develope a self-assembly strategy that relies on sodiumd-an assembly director that passivates the surface of the QDs and induces self-assembly to form ordered three-dimensional cubic structures. A density functional theory model that accounts for the attraction forces between QDs allows to explain self-assembly and superlattice formation. Compared to conventional organic-ligand-passivated QDs, sodium enables higher attractive forces, ultimately leading to the formation of micron-length scale structures and the optical faceting required for feedback. Simultaneously, the decreased inter-dot distance enabled by the new ligand enhances exciton delocalization among QDs, as demonstrated by the dynamically red-shifted photoluminescence. These structures function as the lasing cavity and the gain medium, enabling nanosecond-sustained lasing with a threshold of 25 µJ cm-2 .

Self-Assembled Biophotonic Lasing Network Driven by Amyloid Fibrils in Microcavities

Self-assembled biological structures have played a significant role in many living systems for its functionality and distinctiveness. Here, we experimentally demonstrate that the random dynamic behavior of strong light-matter interactions in complex biological structures can provide hidden information on optical coupling in a network. The concept of biophotonic lasing network is therefore introduced, where a self-assembled human amyloid fibril network was confined in a Fabry-Perot optical cavity. Distinctive lasing patterns were discovered from self-assembled amyloids with different structural dimensions (0D, 1D, 2D, and 3D) confined in a microcavity. Network laser emission exhibiting evidence of light coupling at different wavelengths and locations was spectrally resolved. Dynamic changes of lasing patterns can therefore be interpreted into a graph to reveal the optical correlation in biophotonic networks. Our findings indicate that each graph represents the highly unclonable features of a self-assembled network which can sensitively respond to environmental stimulus. This study offers the potential for studying dynamic biological networks through amplified interactions, shedding light on the development of biologically controlled photonic devices, biosensing, and information encryption.

Resonantly Pumped Bright-Triplet Exciton Lasing in Cesium Lead Bromide Perovskites

The surprising recent observation of highly emissive triplet-states in lead halide perovskites accounts for their orders-of-magnitude brighter optical signals and high quantum efficiencies compared to other semiconductors. This makes them attractive for future optoelectronic applications, especially in bright low-threshold nanolasers. While nonresonantly pumped lasing from all-inorganic lead-halide perovskites is now well-established as an attractive pathway to scalable low-power laser sources for nano-optoelectronics, here we showcase a resonant optical pumping scheme on a fast triplet-state in CsPbBr₃ nanocrystals. The scheme allows us to realize a polarized triplet-laser source that dramatically enhances the coherent signal by 1 order of magnitude while suppressing noncoherent contributions. The result is a source with highly attractive technological characteristics, including a bright and polarized signal and a high stimulated-to-spontaneous emission signal contrast that can be filtered to enhance spectral purity. The emission is generated by pumping selectively on a weakly confined excitonic state with a Bohr radius ∼10 nm in the nanocrystals. The exciton fine-structure is revealed by the energy-splitting resulting from confinement in nanocrystals with tetragonal symmetry. We use a linear polarizer to resolve 2-fold nondegenerate sublevels in the triplet exciton and use photoluminescence excitation spectroscopy to determine the energy of the state before pumping it resonantly.

Laser Emission of Thioflavin T Uncovers Protein Aggregation in Amyloid Nucleation Phase

There is currently no definitive test for early detection of neurodegeneration which is linked with protein aggregation. Finding methods capable of detecting intermediate states of protein aggregates, named oligomers, is critical for the early stage diagnosis of over 30 neurodegenerative diseases including Alzheimer's or Parkinson's. Currently, fluorescence-based imaging using Thioflavin T (ThT) dye is the gold standard for detecting protein aggregation. It is used to detect aggregation in vitro and in various tissues, including the cerebrospinal fluid (CSF), whereby the disease-related protein recombinant is seeded with the patient's fluid. The major drawback of ThT is its lack of sensitivity to oligomeric forms of protein aggregates. Here, we overcome this limitation by transferring a ThT-oligomer mixture into solid state thin films and detecting fluorescence of ThT amplified in the process of stimulated emission. By monitoring the amplified spontaneous emission (ASE) we achieved a remarkable recognition sensitivity to prefibrillar oligomeric forms of insulin and lysozyme aggregates in vitro, to Aβ42 oligomers in the human protein recombinants seeded with CSF and to Aβ42 oligomers doped into brain tissue. Seeding with Alzheimer patient's CSF containing Aβ42 and Tau aggregates revealed that only Aβ42 oligomers allowed generating ASE. Thus, we demonstrated that, in contrast to the current state-of-the-art, ASE of ThT, a commonly used histological dye, can be used to detect and differentiate amyloid oligomers and evaluate the risk levels of neurodegenerative diseases to potential patients before the clinical symptoms occur.

Deep-Blue Perovskite Single-Mode Lasing through Efficient Vapor-Assisted Chlorination

Metal halide perovskites have emerged as promising candidates for solution-processed laser gain materials, with impressive performance in the green and red spectral regions. Despite exciting progress, deep-blue-an important wavelength for laser applications-remains underexplored; indeed, cavity integration and single-mode lasing from large-bandgap perovskites have yet to be achieved. Here, a vapor-assisted chlorination strategy that enables synthesis of low-dimensional CsPbCl₃  thin films exhibiting deep-blue emission is reported. Using this approach,  high-quality perovskite thin films having a low surface roughness (RMS ≈ 1.3 nm) and efficient charge transfer properties are achieved. These enable us to document low-threshold amplified spontaneous emission. Levering the high quality of the gain medium,  vertical-cavity surface-emitting lasers with a low lasing threshold of 6.5 µJ cm^-2  are fabricated. This report of deep-blue perovskite single-mode lasing showcases the prospect of increasing the range of deep-blue laser sources.

Graphene H-Waveguide for Terahertz Lasing Applications: Electromagnetic Quasi-Linear Theory

A novel graphene H-waveguide is proposed for active terahertz components. A graphene film illuminated by strong pumping light shorts the parallel conductor plates. The terahertz modes propagating along this film are amplified at certain conditions. A rigorous electromagnetic (EM) quasi-linear method of analytical calculations of TEy and TMy eigenmodes is used in this paper to select these conditions. Among them is the use of bound TEy modes interacting with graphene plasmons at frequencies of negative graphene resistance, minimizing conductor loss associated with parallel plates, and excluding the current-crowding effect from the waveguide design. The limitations of the used theory are considered, and the applications of this waveguide are proposed.

Perovskite-Gallium Phosphide Platform for Reconfigurable Visible-Light Nanophotonic Chip

Reduction of the wavelength in on-chip light circuitry is critically important not only for the sake of keeping up with Moore's law for photonics but also for reaching toward the spectral ranges of operation of emerging materials, such as atomically thin semiconductors, vacancy-based single-photon emitters, and quantum dots. This requires efficient and tunable light sources as well as compatible waveguide networks. For the first challenge, halide perovskites are prospective materials that enable cost-efficient fabrication of micro- and nanolasers. On the other hand, III-V semiconductor nanowires are optimal for guiding of visible light as they exhibit a high refractive index as well as excellent shape and crystalline quality beneficial for strong light confinement and long-range waveguiding. Here, we develop an integrated platform for visible light that comprises gallium phosphide (GaP) nanowires directly embedded into compact CsPbBr₃-based light sources. In our devices, perovskite microcrystals support stable room-temperature lasing and broadband chemical tuning of the emission wavelength in the range of 530-680 nm, whereas GaP nanowaveguides support efficient outcoupling of light, its subwavelength (<200 nm) confinement, and long-range guiding over distances more than 20 μm. As a highlight of our approach, we demonstrate sequential transfer and conversion of light using an intermediate perovskite nanoparticle in a chain of GaP nanowaveguides.

Room-Temperature Lasing from Mie-Resonant Nonplasmonic Nanoparticles

Subwavelength particles supporting Mie resonances underpin a strategy in nanophotonics for efficient control and manipulation of light by employing both an electric and a magnetic optically induced multipolar resonant response. Here, we demonstrate that monolithic dielectric nanoparticles made of CsPbBr₃ halide perovskites can exhibit both efficient Mie-resonant lasing and structural coloring in the visible and near-IR frequency ranges. We employ a simple chemical synthesis with nearly epitaxial quality for fabricating subwavelength cubes with high optical gain and demonstrate single-mode lasing governed by the Mie resonances from nanocubes as small as 310 nm by the side length. These active nanoantennas represent the most compact room-temperature nonplasmonic nanolasers demonstrated until now.

Light-Emitting Nanophotonic Designs Enabled by Ultrafast Laser Processing of Halide Perovskites

Nanophotonics based on resonant nanostructures and metasurfaces made of halide perovskites have become a prospective direction for efficient light manipulation at the subwavelength scale in advanced photonic designs. One of the main challenges in this field is the lack of large-scale low-cost technique for subwavelength perovskite structures fabrication preserving highly efficient luminescence. Here, unique properties of halide perovskites addressed to their extremely low thermal conductivity (lower than that of silica glass) and high defect tolerance to apply projection femtosecond laser lithography for nanofabrication with precise spatial control in all three dimensions preserving the material luminescence efficiency are employed. Namely, with CH₃ NH₃ PbI₃ perovskite highly ordered nanoholes and nanostripes of width as small as 250 nm, metasurfaces with periods less than 400 nm, and nanowire lasers as thin as 500 nm, corresponding to the state-of-the-art in multistage expensive lithographical methods are created. Remarkable performance of the developed approach allows to demonstrate a number of advanced optical applications, including morphology-controlled photoluminescence yield, structural coloring, optical- information encryption, and lasing.

Halide Perovskites for Nonlinear Optics

Halide perovskites provide an ideal platform for engineering highly promising semiconductor materials for a wide range of applications in optoelectronic devices, such as photovoltaics, light-emitting diodes, photodetectors, and lasers. More recently, increasing research efforts have been directed toward the nonlinear optical properties of halide perovskites because of their unique chemical and electronic properties, which are of crucial importance for advancing their applications in next-generation photonic devices. Here, the current state of the art in the field of nonlinear optics (NLO) in halide perovskite materials is reviewed. Halide perovskites are categorized into hybrid organic/inorganic and pure inorganic ones, and their second-, third-, and higher-order NLO properties are summarized. The performance of halide perovskite materials in NLO devices such as upconversion lasers and ultrafast laser modulators is analyzed. Several potential perspectives and research directions of these promising materials for nonlinear optics are presented.

Deep Blue Light Amplification from a Novel Triphenylamine Functionalized Fluorene Thin Film

The development of high performance optically pumped organic lasers operating in the deep blue still remains a big challenge. In this paper, we have investigated the photophysics and the optical gain characteristics of a novel fluorene oligomer functionalized by four triphenylamine (TPA) groups. By ultrafast spectroscopy we found a large gain spectral region from 420 to 500 nm with a maximum gain cross-section of 1.5 × 10⁻¹⁶ cm² which makes this molecule a good candidate for photonic applications. Amplified Spontaneous Emission measurements (ASE) under 150 fs and 3 ns pump pulses have revealed a narrow emission at 450 nm with a threshold of 5.5 μJcm⁻² and 21 μJcm⁻² respectively. Our results evidence that this new fluorene molecule is an interesting material for photonic applications, indeed the inclusion of TPA as a lateral substituent leads to a high gain and consequently to a low threshold blue organic ASE.

Lanthanide-Based Luminescent Materials for Waveguide and Lasing

Microlasers and waveguides have wide applications in the fields of photonics and optoelectronics. Lanthanide-doped luminescent materials featuring large Stokes/anti-Stokes shift, long excited-state lifetime as well as sharp emission bandwidth are excellent optical components for photonic applications. In the past few years, great progress has been made in the design and fabrication of lanthanide-based waveguides and lasers at the micrometer length scale. Waveguide structures and microcavities can be fabricated from lanthanide-doped amorphous materials through top-down process. Alternatively, lanthanide-doped organic compounds featuring large absorption cross-section can self-assemble into low-dimensional structures of well-defined size and morphology. In recent years, lanthanide-doped crystalline structures displaying highly tunable excitation and emission properties have emerged as promising waveguide and lasing materials, which substantially extends the range of lasing wavelength. In this minireview, we discuss recent advances in lanthanide-based luminescent materials that are designed for waveguide and lasing applications. We also attempt to highlight challenging problems of these materials that obstacle further development of this field.

Fluorescence and Time-Delayed Lasing during Single Laser Pulse Excitation of a Pendant mm-Sized Dye Droplet

Fluorescence and lasing emission that are produced separately in time during excitation laser pulse for an mm-sized Rhodamine 6G dye-water droplet are reported. The droplet acts as a quasi-spherical closed optical resonator and due to multiple internal reflections, the resonant amplified emission is delayed with respect to fluorescence emission. Measurements of the temporal evolution of the droplet’s emission were performed by varying the signal acquisition gate width and gate delay with respect to the pumping pulse. The droplet emission spectra are structured in two bands which appear one after the other in time: first, the fluorescence emission band which follows pumping laser pulse time shape and then a second band, the lasing band, placed at shorter wavelengths and formed in time after the peak of the pumping laser pulse intensity, on the pulse tail. The lasing threshold pumping intensity is much lower than those for typical dye lasers.

Lead-Free Perovskites for Lighting and Lasing Applications: A Minireview

Research on materials with perovskite crystal symmetry for photonics applications represent a rapidly growing area of the photonics development due to their unique optical and electrical properties. Among them are high charge carrier mobility, high photoluminescence quantum yield, and high extinction coefficients, which can be tuned through all visible range by a controllable change in chemical composition. To date, most of such materials contain lead atoms, which is one of the obstacles for their large-scale implementation. This disadvantage can be overcome via the substitution of lead with less toxic chemical elements, such as Sn, Bi, Yb, etc., and their mixtures. Herein, we summarized the scientific works from 2016 related to the lead-free perovskite materials with stress on the lasing and lighting applications. The synthetic approaches, chemical composition, and morphology of materials, together with the optimal device configurations depending on the material parameters are summarized with a focus on future challenges.

Vapor-Phase Incommensurate Heteroepitaxy of Oriented Single-Crystal CsPbBr3 on GaN: Toward Integrated Optoelectronic Applications

Integrating metallic halide perovskites with established modern semiconductor technology is significant for promoting the development of application-level optoelectronic devices. To realize such devices, exploring the growth dynamics and interfacial carrier dynamics of perovskites deposited on the core materials of semiconductor technology is essential. Herein, we report the incommensurate heteroepitaxy of highly oriented single-crystal cesium lead bromide (CsPbBr₃) on c-wurtzite GaN/sapphire substrates with atomically smooth surface and uniform rectangular shape by chemical vapor deposition. The CsPbBr₃ microplatelet crystal exhibits green-colored lasing under room temperature and has a structural stability comparable with that grown on van der Waals mica substrates. Time-resolved photoluminescence spectroscopy studies show that the type-II CsPbBr₃-GaN heterojunction effectively enhances the separation and extraction of free carriers inside CsPbBr₃. These findings provide insights into the fabrication and application-level integrated optoelectronic devices of CsPbBr₃ perovskites.

Lasing from Mechanically Exfoliated 2D Homologous Ruddlesden-Popper Perovskite Engineered by Inorganic Layer Thickness

2D Ruddlesden-Popper perovskites (RPPs) have aroused growing attention in light harvesting and emission applications owing to their high environmental stability. Recently, coherent light emission of RPPs was reported, however mostly from inhomologous thin films that involve cascade intercompositional energy transfer. Lasing and fundamental understanding of intrinsic laser dynamics in homologous RPPs free from intercompositional energy transfer is still inadequate. Herein, the lasing and loss mechanisms of homologous 2D (BA)₂ (MA)_{n -1} Pb_n I_{3 n +1} RPP thin flakes mechanically exfoliated from the bulk crystal are reported. Multicolor lasing is achieved from the large-n RPPs (n ≥ 3) in the spectral range of 620-680 nm but not from small-n RPPs (n ≤ 2) even down to 78 K. With decreasing n, the lasing threshold increases significantly and the characteristic temperature decreases as 49, 25, and 20 K for n = 5, 4, and 3, respectively. The n-engineered lasing behaviors are attributed to the stronger Auger recombination and exciton-phonon interaction as a result of the enhanced quantum confinement in the smaller-n perovskites. These results not only advance the fundamental understanding of loss mechanisms in both inhomologous and homologous RPP lasers but also provide insights into developing low-threshold, substrate-free, and multicolor 2D semiconductor microlasers.

Polarization-Dependent Lasing Behavior from Low-Symmetry Nanocavity Arrays

This paper reports how geometric effects in low-symmetry plasmonic nanoparticle arrays can produce polarization-dependent lasing responses. We developed a scalable fabrication procedure to pattern rhombohedral arrays of aluminum anisotropic nanoparticles that support lattice plasmon modes from both first-order and second-order diffraction coupling. We found that nanoparticle shape can be used to engineer the spatial overlap between electromagnetic hot spots of different lattice modes and dye gain to support plasmonic lasing. The lasing behavior revealed that plasmon-exciton energy transfer depends on polarization, with stronger coupling and faster dynamics when the transition dipole moments of the excited gain are aligned with the electric field of the plasmon modes.

Strong Light-Field Driven Nanolasers

Einstein established the quantum theory of radiation and paved the way for modern laser physics including single-photon absorption by charge carriers and finally pumping an active gain medium into population inversion. This can be easily understood in the particle picture of light. Using intense, ultrashort pulse lasers, multiphoton pumping of an active medium has been realized. In this nonlinear interaction regime, excitation and population inversion depend not only on the photon energy but also on the intensity of the incident pumping light, which can be still described solely by the particle picture of light. We demonstrate here that lowering significantly the pump photon energy further still enables population inversion and lasing in semiconductor nanowires. The extremely high electric field of the pump bends the bands and enables tunneling of electrons from the valence to the conduction band. In this regime, the light acts by the classical Coulomb force and population inversion is entirely due to the wave nature of electrons, thus the excitation becomes independent of the frequency but solely depends on the incident intensity of the pumping light.

Lasing Supraparticles Self-Assembled from Nanocrystals

One of the most attractive commercial applications of semiconductor nanocrystals (NCs) is their use in lasers. Thanks to their high quantum yield, tunable optical properties, photostability, and wet-chemical processability, NCs have arisen as promising gain materials. Most of these applications, however, rely on incorporation of NCs in lasing cavities separately produced using sophisticated fabrication methods and often difficult to manipulate. Here, we present whispering gallery mode lasing in supraparticles (SPs) of self-assembled NCs. The SPs composed of NCs act as both lasing medium and cavity. Moreover, the synthesis of the SPs, based on an in-flow microfluidic device, allows precise control of the dimensions of the SPs, i.e. the size of the cavity, in the micrometer range with polydispersity as low as several percent. The SPs presented here show whispering gallery mode resonances with quality factors up to 320. Whispering gallery mode lasing is evidenced by a clear threshold behavior, coherent emission, and emission lifetime shortening due to the stimulation process.

Temperature Difference Triggering Controlled Growth of All-Inorganic Perovskite Nanowire Arrays in Air

All-inorganic perovskites have attracted increasing worldwide interest due to its significantly improved stability in atmospheric environment compared to organic-inorganic hybrid perovskites, which renders it infinitely applicable in many fields such as electronics, optoelectronics, and energy storage. However, all-inorganic perovskites have to confront the challenges from fabrication before their wide utilization in the aforementioned applications. Liquid-phase synthesis holds the advantage of mass production and easy modulation of composition but with the deficiencies of relatively low crystallinity and disordered products. Interestingly, gas-phase growth has complementary characteristics compared to the liquid-phase method. In this work, it is proposed that a novel temperature difference triggers growth strategy to integrate the merits of the liquid- and gas-phase methods, and the feasibility of this strategy via a simple lab-use hot plate is demonstrated. High quality all-inorganic perovskites, cesium lead halide (CsPbX₃ ) nanowire arrays, can be epitaxially grown as in a gas-phase method, but at the same time, the composition of products can be easily modulated by predesigning the recipe of precursors as in the liquid-phase method on a large scale. Notably, the as-fabricated CsPbX₃ perovskite nanowire arrays demonstrate excellent stability and good optoelectronic properties in air. It is believed that this novel strategy can strikingly prompt the development of perovskites fabrication and applications in future.

Compound Glass Microsphere Resonator Devices

In recent years, compound glass microsphere resonator devices have attracted increasing interest and have been widely used in sensing, microsphere lasers, and nonlinear optics. Compared with traditional silica resonators, compound glass microsphere resonators have many significant and attractive properties, such as high-Q factor, an ability to achieve high rare earth ion, wide infrared transmittance, and low phonon energy. This review provides a summary and a critical assessment of the fabrication and the optical characterization of compound glasses and the related fabrication and applications of compound glass microsphere resonators.

Self-Assembled Photonic Crystals of Monodisperse Dendritic Fibrous Nanosilica for Lasing: Role of Fiber Density

Photonic crystals are essentially a periodic ("crystalline") arrangement of dielectric nanoparticles that respond in unison to incident light. They can be used to harvest light in various applications such as photocatalysis, solar cells, and lasing. In this work, we prepared the photonic crystals of dendritic fibrous nanosilica (DFNS) by their self-assembly. Because of the narrow particle size distribution of the as-synthesized DFNS, they readily formed colored photonic crystals. The photonic band gap was found to be tunable by using DFNS of various sizes and fiber densities. Notably, even after having similar particle sizes (but with different fiber densities), they showed different photonic band gaps, indicating that the fiber density plays a role in the band gap of photonic crystals. Such observations have not been reported before. This could have arisen from the difference in their refractive indices because of the difference in their fiber densities and hence the variation in the silica content, leading to a different optical signature.

Low-Threshold Lasing from 2D Homologous Organic-Inorganic Hybrid Ruddlesden-Popper Perovskite Single Crystals

Organic-inorganic hybrid two-dimensional (2D) perovskites have recently attracted great attention in optical and optoelectronic applications due to their inherent natural quantum-well structure. We report the growth of high-quality millimeter-sized single crystals belonging to homologous two-dimensional (2D) hybrid organic-inorganic Ruddelsden-Popper perovskites (RPPs) of (BA)₂(MA) _n-1Pb _nI_{3 n+1} ( n = 1, 2, and 3) by a slow evaporation at a constant-temperature (SECT) solution-growth strategy. The as-grown 2D hybrid perovskite single crystals exhibit excellent crystallinity, phase purity, and spectral uniformity. Low-threshold lasing behaviors with different emission wavelengths at room temperature have been observed from the homologous 2D hybrid RPP single crystals. Our result demonstrates that solution-growth homologous organic-inorganic hybrid 2D perovskite single crystals open up a new window as a promising candidate for optical gain media.

Direct Identification of Surface Defects and Their Influence on the Optical Characteristics of Upconversion Nanoparticles

Core-shell structure is an obvious concept to suppress surface-related deactivations in lanthanide-doped upconversion nanoparticles (UCNPs). However, no direct observation of atomic-scale surface restoration, which can improve the upconversion photoluminescence, has been reported. Here, we use aberration-corrected high-angle annular dark field scanning transmission electron microscopy to study the surface condition of KLu₂F₇:Yb³⁺,Er³⁺ bare core UCNPs. Due to the very thin and uniform thickness of the UCNPs, we observe unambiguously that the recovery from surface defects enhances upconversion photoluminescence. Furthermore, the realization of dominant green lasing emission under pulsed laser excitation confirms the high crystallinity of the UCNPs.

Fabry-Pérot Oscillation and Room Temperature Lasing in Perovskite Cube-Corner Pyramid Cavities

Recently, organometal halide perovskite-based optoelectronics, particularly lasers, have attracted intensive attentions because of its outstanding spectral coherence, low threshold, and wideband tunability. In this work, high-quality CH₃ NH₃ PbBr₃ single crystals with a unique shape of cube-corner pyramids are synthesized on mica substrates using chemical vapor deposition method. These micropyramids naturally form cube-corner cavities, which are eminent candidates for small-sized resonators and retroreflectors. The as-grown perovskites show strong emission ≈530 nm in the vertical direction at room temperature. A special Fabry-Pérot (F-P) mode is employed to interpret the light confinement in the cavity. Lasing from the perovskite pyramids is observed from 80 to 200 K, with threshold ranging from ≈92 µJ cm^-2 to 2.2 mJ cm^-2 , yielding a characteristic temperature of T₀ = 35 K. By coating a thin layer of Ag film, the threshold is reduced from ≈92 to 26 µJ cm^-2 , which is accompanied by room temperature lasing with a threshold of ≈75 µJ cm^-2 . This work advocates the prospect of shape-engineered perovskite crystals toward developing micro-sized optoelectronic devices and potentially investigating light-matter coupling in quantum optics.