Electrically Driven White Light Emission from Intrinsic Metal–Organic Framework

Light-emitting diodes (LEDs) have drawn tremendous potential as a replacement of traditional lighting due to its low-power consumption and longer lifetime. Nowadays, the practical white LEDs (WLED) are contingent on the photon down-conversion of phosphors containing rare-earth elements, which limits its utility, energy, and cost efficiency. In order to resolve the energy crisis and to address the environmental concerns, designing a direct WLED is highly desirable and remains a challenging issue. To circumvent the existing difficulties, in this report, we have designed and demonstrated a direct WLED consisting of a strontium-based metal–organic framework (MOF), {[Sr­(ntca)­(H₂O)₂]·H₂O}_<i>n</i> (<b>1</b>), graphene, and inorganic semiconductors, which can generate a bright white light emission. In addition to the suitable design of a MOF structure, the demonstration of electrically driven white light emission based on a MOF is made possible by the combination of several factors including the unique properties of graphene and the appropriate band alignment between the MOF and semiconductor layer. Because electroluminescence using a MOF as an active material is very rare and intriguing and a direct WLED is also not commonly seen, our work here therefore represents a major discovery which should be very useful and timely for the development of solid-state lighting

Electrically Driven White Light Emission from Intrinsic Metal–Organic Framework

Light-emitting diodes (LEDs) have drawn tremendous potential as a replacement of traditional lighting due to its low-power consumption and longer lifetime. Nowadays, the practical white LEDs (WLED) are contingent on the photon down-conversion of phosphors containing rare-earth elements, which limits its utility, energy, and cost efficiency. In order to resolve the energy crisis and to address the environmental concerns, designing a direct WLED is highly desirable and remains a challenging issue. To circumvent the existing difficulties, in this report, we have designed and demonstrated a direct WLED consisting of a strontium-based metal–organic framework (MOF), {[Sr­(ntca)­(H₂O)₂]·H₂O}_<i>n</i> (<b>1</b>), graphene, and inorganic semiconductors, which can generate a bright white light emission. In addition to the suitable design of a MOF structure, the demonstration of electrically driven white light emission based on a MOF is made possible by the combination of several factors including the unique properties of graphene and the appropriate band alignment between the MOF and semiconductor layer. Because electroluminescence using a MOF as an active material is very rare and intriguing and a direct WLED is also not commonly seen, our work here therefore represents a major discovery which should be very useful and timely for the development of solid-state lighting

Whispering Gallery Mode Lasing from Self-Assembled Hexagonal Perovskite Single Crystals and Porous Thin Films Decorated by Dielectric Spherical Resonators

Lasing in self-assembled hybrid organic–inorganic lead halide perovskites semiconductors has attained intensive research for low cost and high performance optoelectronic devices due to their inherent outstanding optical response. However, to achieve the controllable laser action from a small single crystal remains as a challenging issue. Here, we present a novel technique to fabricate self-assembled high-quality hexagonal perovskite single crystals for realizing room-temperature near-infrared whispering-gallery-mode (WGM) laser action. Quite interestingly, the lasing spectrum for an individual CH₃NH₃PbI₃ hexagonal single crystals encompasses the aspects of high quality factor (<i>Q</i>) and low threshold WGM lasing around 1200 and 26.8 μJ/cm², respectively. In addition, we demonstrate that when the porous perovskite thin films were decorated with dielectric spheres, the laser oscillation can be achieved through the coupling of WGM with perovskite gain material. We found that the lasing spectra can be well manipulated by the size of hexagonal single crystals and SiO₂ spheres. Moreover, the discovered laser action and chemical stability of hexagonal single crystal perovskites not only render them significant practical use in highly efficient near-infrared emitting devices for laser photonics, solid-state lighting, and display applications, but also provide a potential extension toward various optoelectronic devices

Highly Stretchable and Sensitive Photodetectors Based on Hybrid Graphene and Graphene Quantum Dots

Stretchable devices possess great potential in a wide range of applications, such as biomedical and wearable gadgets and smart skin, which can be integrated with the human body. Because of their excellent flexibility, two-dimensional (2D) materials are expected to play an important role in the fabrication of stretchable devices. However, only a limited number of reports have been devoted to investigating stretchable devices based on 2D materials, and the stretchabilities were restricted in a very small strain. Moreover, there is no report related to the stretchable photodetectors derived from 2D materials. Herein, we demonstrate a highly stretchable and sensitive photodetector based on hybrid graphene and graphene quantum dots (GQDs). A unique rippled structure of poly­(dimethylsiloxane) is used to support the graphene layer, which can be stretched under an external strain far beyond published reports. The ripple of the device can overcome the native stretchability limit of graphene and enhance the carrier generation in GQDs due to multiple reflections of photons between the ripples. Our strategy presented here can be extended to many other material systems, including other 2D materials. It therefore paves a key step for the development of stretchable electronics and optical devices

Semiconductor Behavior of a Three-Dimensional Strontium-Based Metal–Organic Framework

The self-assembly of a three-dimensional strontium-based metal–organic framework [Sr­(Hbtc)­(H₂O)]_<i>n</i> (<b>1</b>) was achieved through the reaction of Sr­(NO₃)₂ with a 1,2,4-benzenetricarboxylic acid (1,2,4-H₃btc) ligand under hydrothermal conditions. This Sr-based metal–organic framework exhibits remarkable semiconducting behavior, as evidenced by theoretical calculations and experimental measurements. Temperature-dependent DC conductivity, near-room-temperature AC conductivity, diffuse reflection spectra, and photoluminescence spectra provide strong proof that compound <b>1</b> shows a band gap of 2.3 eV, which is comparable to that for other commonly available semiconducting materials (e.g., CdSe, CdTe, ZnTe, GaP, etc.). The optimized molecular structure and electronic properties (density of states and band gap energy) of <b>1</b> were calculated using density functional theory, and the results are consistent with experimental findings. This is the first report on the semiconducting properties of a strontium-based MOF, which will pave the way for further studies in semiconducting MOFs with interesting potential applications in optoelectronic devices

Chiral Light Emission from a Hybrid Magnetic Molecule–Monolayer Transition Metal Dichalcogenide Heterostructure

Hybrid layered materials assembled from atomically thin crystals and small molecules bring great promises in pushing the current information and quantum technologies beyond the frontiers. We demonstrate here a class of layered valley–spin hybrid (VSH) materials composed of a monolayer two-dimensional (2D) semiconductor and double-decker single molecule magnets (SMMs). We have materialized a VSH prototype by thermal evaporation of terbium bis-phthalocyanine onto a MoS2 monolayer and revealed its composition and stability by both microscopic and spectroscopic probes. The interaction of the VSH components gives rise to the intersystem crossing of the photogenerated carriers and moderate p-doping of the MoS2 monolayer, as corroborated by the density functional theory calculations. We further explored the valley contrast by helicity-resolved photoluminescence (PL) microspectroscopy carried out down to liquid helium temperatures and in the presence of the external magnetic field. The most striking feature of the VSH is the enhanced A exciton-related valley emission observed at the out-of-resonance condition at room temperature, which we elucidated by the proposed nonradiative energy drain transfer mechanism. Our study thus demonstrates the experimental feasibility and great promises of the ultrathin VSH materials with chiral light emission, operable by physical fields for emerging opto-spintronic, valleytronic, and quantum information concepts

Integration of Nanoscale Light Emitters and Hyperbolic Metamaterials: An Efficient Platform for the Enhancement of Random Laser Action

Hyperbolic metamaterials have emerged as novel materials with exciting functionalities, especially for optoelectronic devices. Here, we provide the first attempt to integrate hyperbolic metamaterials with light emitting nanostructures, which enables to strongly enhance random laser action with reduced lasing threshold. Interestingly, the differential quantum efficiency can be enhanced by more than four times. The underlying mechanism can be interpreted well based on the fact that the high-<i>k</i> modes excited by hyperbolic metamaterials can greatly increase the possibility of forming close loops decreasing the energy consumption for the propagation of scattered photons in the matrix. In addition, out-coupled propagation of the high-<i>k</i> modes reaches to the far-field without being trapped inside the metamaterials due to the coupling with the random distribution of light emitting nanoparticles also plays an important role. Electromagnetic simulations derived from the finite-difference time-domain (FDTD) method are executed to support our interpretation. Realizing strong enhancement of laser action assisted by hyperbolic metamaterials provides an attractive, very simple and efficient scheme for the development of high performance optoelectronic devices, including phototransistors, and many other solid state lighting systems. Besides, because of increasing light absorption assisted by hyperbolic metamaterials structure, our approach shown is also useful for the application of highly efficient solar cells

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)_{<i><i>n</i></i>−1}Pb_{<i><i>n</i></i>}I_{3<i><i>n</i></i>+1} (<i>n</i> = 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

Transparent, Wearable, Broadband, and Highly Sensitive Upconversion Nanoparticles and Graphene-Based Hybrid Photodetectors

Numerous investigations of photon upconversion in lanthanide-doped upconversion nanoparticles (UCNPs) have led to its application in the fields of bioimaging, biodetection, cancer therapy, displays, and energy conversion. Herein, we demonstrate a new approach toward lanthanide-doped UCNPs and a graphene hybrid planar and rippled structure photodetector. The multi-energy sublevels from the 4fⁿ electronic configuration of lanthanides results in longer excited state lifetime for photogenerated charge carriers. This opens up a new regime for ultra-high-sensitivity and broadband photodetection. Under 808 nm infrared light illumination, the planar hybrid photodetector shows a photoresponsivity of 190 AW^–1, which is higher than the currently reported responsivities of the same class of devices. Also, the rippled graphene and UCNPs hybrid photodetector on a poly­(dimethylsiloxane) substrate exhibits an excellent stretchability, wearability, and durability with high photoresponsivity. This design makes a significant contribution to the ongoing research in the field of wearable and stretchable optoelectronic devices

Plasmonic Carbon-Dot-Decorated Nanostructured Semiconductors for Efficient and Tunable Random Laser Action

Carbon dots have emerged as popular materials in various research fields, including biological and photovoltaic areas, while significant reports are lacking related to their applications in laser devices, which play a significant role in our daily life. In this work, we demonstrate the first controllable random laser assisted by the surface plasmon effect of carbon dots. Briefly, carbon dots derived from candle soot are randomly deposited on the surface of gallium nitride (GaN) nanorods to enhance the ultraviolet fluorescence of GaN and generate plasmonically enhanced random laser action with coherent feedback. Furthermore, potentially useful functionalities of tunable lasing threshold and controllable optical modes are achieved by adjusting the numbers of carbon dots, enabling applications in optical communication and identification technologies. In addition to providing an efficient alternative for plasmonically enhanced random laser devices with simple fabrication and low cost, our work also paves a useful route for the application of environmentally friendly carbon dots in optoelectronic devices