3D organic-inorganic hybrid perovskites have featured high gain coefficients through the electron-hole plasma stimulated emission mechanism, while their 2D counterparts of Ruddlesden-Popper perovskites (RPPs) exhibit strongly bound electron-hole pairs (excitons) at room temperature. High-performance solar cells and light-emitting diodes (LEDs) are reported based on 2D RPPs, whereas light-amplification devices remain largely unexplored. Here, it is demonstrated that ultrafast energy transfer along cascade quantum well (QW) structures in 2D RPPs concentrates photogenerated carriers on the lowest-bandgap QW state, at which population inversion can be readily established enabling room-temperature amplified spontaneous emission and lasing. Gain coefficients measured for 2D RPP thin-films (≈100 nm in thickness) are found about at least four times larger than those for their 3D counterparts. High-density large-area microring arrays of 2D RPPs are fabricated as whispering-gallery-mode lasers, which exhibit high quality factor (Q ≈ 2600), identical optical modes, and similarly low lasing thresholds, allowing them to be ignited simultaneously as a laser array. The findings reveal that 2D RPPs are excellent solution-processed gain materials potentially for achieving electrically driven lasers and ideally for on-chip integration of nanophotonics.

Abstract2D Ruddlesden–Popper perovskites (RPPs) are a class of quantum‐well (QW) materials, composed of layered perovskite QWs encapsulated between two hydrophobic organic layers. Different from widely investigated 3D‐perovskites with free carriers at room temperature, 2D‐RPPs exhibit strongly bound electron–hole pairs (excitons) for high‐performance solar cells and light emitting diodes (LEDs). Herein, it is reported that self‐organized multiple QWs in 2D‐RPP thin films naturally form an energy cascade, which enables an ultrafast energy transfer process from higher energy‐bandgap QWs to lower energy‐bandgap QWs. Therefore, photoexcitations are concentrated on lower‐bandgap QWs, facilitating the build‐up of population inversion. Room‐temperature amplified spontaneous emission (ASE) from 2D‐RPP thin films is achieved at dramatically low thresholds, with gain coefficients as high as >300 cm−1, and stoichiometrically tunable ASE wavelengths from visible to near‐infrared spectral range (530–810 nm). In view of the high efficiency reported for LEDs, these solution‐processed 2D‐RPP thin films may hold the key to realize electrically driven lasers.

Zero-dimensional (0D) perovskite CsPbBr has been speculated to be an efficient solid-state emitter, exhibiting strong luminescense on achieving quantum confinement. Although several groups have reported strong green luminescence from CsPbBr powders and nanocrystals, doubts that the origin of luminescence comes from CsPbBr itself or CsPbBr impurities have been a point of controversy in recent investigations. Herein, we developed a facile one-step solution self-assembly method to synthesize pure zero-dimensional rhombohedral CsPbBr micro-disks (MDs) with a high PLQY of 52% ± 5% and photoluminescence full-width at half maximum (FWHM) of 16.8 nm. The obtained rhombohedral MDs were high quality single-crystalline as demonstrated by XRD and SAED patterns. We demonstrated that CsPbBr MDs and CsPbBr MDs were phase-separated from each other and the strong green emission comes from CsPbBr. Power and temperature dependence spectra evidenced that the observed strong green luminescence of pure CsPbBr MDs originated from direct exciton recombination in the isolated octahedra with a large binding energy of 303.9 meV. Significantly, isolated PbBr octahedra separated by a Cs ion insert in the crystal lattice is beneficial to maintaining the structural stability, depicting superior thermal and anion exchange stability. Our study provides an efficient approach to obtain high quality single-crystalline CsPbBr MDs with highly efficient luminescence and stability for further optoelectronic applications.

Cesium lead halide (CsPbX ) perovskite has emerged as a promising low-threshold multicolor laser material; however, realizing wavelength-tunable lasing output from a single CsPbX nanostructure is still constrained by integrating different composition. Here, the direct synthesis of composition-graded CsPbBr I nanowires (NWs) is reported through vapor-phase epitaxial growth on mica. The graded composition along the NW, with an increased Br/I from the center to the ends, comes from desynchronized deposition of cesium lead halides and temperature-controlled anion-exchange reaction. The graded composition results in varied bandgaps along the NW, which induce a blueshifted emission from the center to the ends. As an efficient gain media, the nanowire exerts position-dependent lasing performance, with a different color at the ends and center respectively above the threshold. Meanwhile, dual-color lasing with a wavelength separation of 35 nm is activated simultaneously at a site with an intermediate composition. This position-dependent dual-color lasing from a single nanowire makes these metal halide perovskites promising for applications in nanoscale optical devices.

Miniaturized nanowire nanolasers of 3D perovskites feature a high gain coefficient; however, room-temperature optical gain and nanowire lasers from 2D layered perovskites have not been reported to date. A biomimetic approach is presented to construct an artificial ligh-harvesting system in mixed multiple quantum wells (QWs) of 2D-RPPs of (BA) (FA) Pb Br , achieving room-temperature ASE and nanowire (NW) lasing. Owing to the improvement of flexible and deformable characteristics provided by organic BA cation layers, high-density large-area NW laser arrays were fabricated with high photostability. Well-controlled dimensions and uniform geometries enabled 2D-RPPs NWs functioning as high-quality Fabry-Perot (FP) lasers with almost identical optical modes, high quality (Q) factor (ca. 1800), and similarly low lasing thresholds.

Mercury is a major threat to the environment and to human health. It is highly desirable to develop a user-friendly kit for on-site mercury detection. Such a method must be able to detect mercury below the threshold levels (10 nM) for drinking water defined by the U.S. Environmental Protection Agency. Herein, we for the first time reported catalytically active gold amalgam-based reaction between 4-nitrophenol and NaBH4 with colorimetric sensing function. We take advantage of the correlation between the catalytic properties and the surface area of gold amalgam, which is proportional to the amount of the gold nanoparticle (AuNP)-bound Hg(2+). As the concentration of Hg(2+) increases until the saturation of Hg onto the AuNPs, the catalytic performance of the gold amalgam is much stronger due to the formation of gold amalgam and the increase of the nanoparticle surface area, leading to the decrease of the reduction time of 4-nitrophenol for the color change. This sensing system exhibits excellent selectivity and ultrahigh sensitivity up to the 1.45 nM detection limit. The practical use of this system for Hg(2+) determination in tap water samples is also demonstrated successfully.

Miniaturized nanowire nanolasers of 3D perovskites feature ah igh gain coefficient;h owever,r oom-temperature optical gain and nanowire lasers from 2D layered perovskites have not been reported to date.Ab iomimetic approach is presented to construct an artificial ligh-harvesting system in mixed multiple quantum wells (QWs) of 2D-RPPs of (BA) 2 -(FA) nÀ1 Pb n Br 3n+1 ,a chieving room-temperature ASE and nanowire (NW) lasing.O wing to the improvement of flexible and deformable characteristics provided by organic BA cation layers,high-density large-area NW laser arrays were fabricated with high photostability.W ell-controlled dimensions and uniform geometries enabled 2D-RPPs NWs functioning as highquality Fabry-Perot (FP) lasers with almost identical optical modes,h igh quality (Q) factor (ca. 1800), and similarly low lasing thresholds.Ever-increasing demands on high-speed optical communication and data processing had stimulated ag reat deal of research interest in nanophotonics. [1] Semiconductor nanowire (NW) lasers are promising as miniaturized building blocks for on-chip integration of photonic circuits,o wing to their ultra-compact physical sizes,h ighly localized coherent output, and efficient wave-guiding. [1b, 2] Forp ractical use, development of NW laser arrays is of great importance for full-color laser displays,l aser lighting, and sensing applications. [3] Nevertheless,monolithic growth and patterning of III-Vs emiconductor NWs onto an arbitrary substrate remains af ormidable task, owing to material lattice mismatch and incompatible growth temperature. [4] Organic-inorganic halide hybrid perovskite materials are an emerging class of solution-processed semiconductors for high-efficiencyoptoelectronic devices, [5] which are promising for solar cells(SCs), [5b] light-emitting diodes (LEDs), [6] optical amplifiers, [7] and optically pumped lasers. [2,8] Recently,3 D perovskite nanowire (NW) lasers were demonstrated with low lasing thresholds and high quality factors. [2] On the one hand, these self-assembly NWs were solution grown with random orientation by exposing al ead acetate film to as olution of MA halide salt. [2] On the other hand, the instability owing to atmospheric moisture and halide ion migration is another challenge in 3D perovskite technology. [9] Tw o-dimensional (2D) organic-inorganic hybrid Ruddlesden-Popper perovskites (RPPs) are solution-processed quantum well (QW) materials [10] that show unique and promising advantages as compared with their 3D counterparts, [11] including both technologically relevant photo-/chemical stability and quantum tunable optoelectronic properties. [12] 2D RPPs adopt ac hemical formula as A' 2 A nÀ1 M n X 3n+1 with A' ao rganic cation larger than A. Thep erovskite framework [A nÀ1 M n X 3n+1 ] 2À layers are sandwiched between two organic layers composed of A' cations. [13] Dielectric constants difference between RPP and organic layers leads to effective confinement of electron-hole pairs within the [A nÀ1 M n X 3n+1 ] 2À layer, therefore inducing excitons th...

Optical resonator arrays are highly important fundamental units for integrated photoelectric devices, such as on‐chip logical circuits, high‐precision sensors, and laser displays. Whispering gallery mode (WGM) microrings (MRs) could reduce the optical losses and provide a small mode volume, which is helpful for the integration of miniaturized devices. However, there still is a great challenge to produce and pattern the circular resonator. Here, a facile poly(dimethylsiloxane) (PDMS) ring‐hole‐stamp confined solution‐growth method is used to fabricate organic (E)‐3‐(4‐(di‐p‐tolylamino)phenyl)‐1‐(1‐hydroxynaphthalen‐2‐yl)prop‐2‐en‐1‐one (DPHP) MR arrays. Low‐threshold multi‐mode near‐infrared lasing is successfully achieved in the single MRs and DPHP MR arrays at room temperature. At the same time, their lasing behaviors change obviously in the lasing intensity, emission position, lasing mode, and lasing threshold after contacting with water and NaOH solution. The present work is a major step for realizing compact near‐infrared optoelectronic devices.