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Hybrid lead halide perovskites have generated increasing attention for their high performance in optoelectronic applications. One main drawback of these materials is the sensitivity to moisture, which contributes heavily to the ultimate decomposition. Here, this study takes advantage of the reported representative white‐light emitting lead bromide perovskite and three‐dimensional (3D) perovskite as the subject of water‐stability study. It is reported here that other than observed phase transformation in one case, the majority of these perovskites break down in water rapidly, precipitating out as an inorganic salt compound Pb3Br6[H2O]·H2O. As these materials are studied in detail, it is discovered that better coverage of the hydrophobic organic cation enhances the water stability. Taking this idea further, it is demonstrated here that five new one‐dimensional (1D) lead bromide compounds have superior water stability, where the longest stability when completely immersed in water is more than one year and counting. This work provides a new mechanism regarding the degradation process when encountering moisture and general guidelines to increase the water stability for the lead bromide hybrids. [ABSTRACT FROM AUTHOR]

Core–shell perovskite nanocrystals (NCs) have emerged as a promising class of materials for optoelectronic applications due to their unique properties and stability. Although much research has been conducted on the shell growth mechanism and properties of the core–shell NCs, little is known about the role of shell thickness in determining their optical properties. Herein, a heteroepitaxial method is employed to prepare a series of core–shell FAPbBr3/CsPbBr3 NCs with different shell thicknesses. Through temperature‐dependent photoluminescence measurement, it is found that the electronic structure of core–shell FAPbBr3/CsPbBr3 NCs evolves from quasi‐type‐II to type‐I with the increase in shell thickness. This abnormal transition can be attributed to the thickened gradient alloy layer FA1‐xCsxPbBr3, which effectively relieves the lattice mismatch and releases strain in the NCs, resulting in variations in the bandgap between the core and the shell. Furthermore, the biexciton Auger lifetimes in these samples exhibit a non‐monotonic dependence on shell thickness, indicating the electronic structure transition. These results provide valuable insights into the relationship between shell thickness, electronic structure, and optical properties in core–shell perovskite NCs, which may offer guidance for the design of high‐performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

Chiral hybrid Cu(I)‐based iodides with d10 closed shell demonstrate great potential for circularly polarized luminescence (CPL) because of high photoluminescence quantum yield (PLQY). Herein, by incorporating mono‐ or bi‐dentate coordination mode ligands as chiral source, the self‐assembly of four pairs of chiral hybrid Cu(I)‐based iodides, namely, (R/S)‐Cu4I4(Hmpy)4·H2O (R/S‐1), (R/S)‐Cu4I4(3Hpy)4 (R/S‐2), (R/S)‐Cu4I4(2MePI)4 (R/S‐3), and (R/S)‐Cu4I4(3AD)4 (R/S‐4) (where R/S‐Hmpy = R/S‐2‐pyrrolidinemethanol, R/S‐3Hpy = R/S‐3‐hydroxypyrrolidine, R/S‐2MePI = R/S‐2‐methylpiperazine, and R/S‐3AD = R/S‐3‐aminopiperidine), are reported. With the monodentate and bidentate ligands, these materials belong to two different structural types: 0D molecular clusters (R/S‐1, R/S‐2) and 3D porous metal–organic frameworks (R/S‐3, R/S‐4). These materials all crystallize in non‐centrosymmetric space groups containing similar basic Cu4I4 cubane tetramer building units but with different coordination modes. They are also semiconductors, with optical bandgaps ranging from 2.70 to 2.94 eV. The photoluminescence (PL) and circularly polarized luminescence (CPL) emissions are further characterized, where the highest PLQY of ≈95% and CPL dissymmetry factor (glum) of ≈7 × 10−3 are achieved in R/S‐1. This work offers a systematic comparison between different structural types with similar building blocks, bridging by the flexible chiral ligands, and shows that the hybrid copper iodides are highly promising candidates for next‐generation optoelectronics and chiroptics. [ABSTRACT FROM AUTHOR]

As the most promising candidate for luminescent semiconductor materials in the future environmentally friendly society, InP nanocrystals (NCs) have attracted strong attention in the past decade. Tremendous efforts have been devoted to address the unstable and poor optical properties of InP NCs for practical applications. An extensive and in‐depth summary of existing literatures can not only provide an important reference for further optimizing of the optical properties of InP NCs, but also lay a foundation for subsequent related applications. In this review, the methods for the synthesis with different P sources and different ZnE (E = Se, S) shells are briefly summarized. The research progress in the optical properties investigation of InP/ZnE and InP/ZnE/ZnE NCs, including absorption, fluorescence, carrier dynamics, and nonlinear optics, are summarized. The relevant applications based on InP/ZnE and InP/ZnE/ZnE NCs are also presented, ranging from light emitting diodes, bioimaging, and solar cells to photocatalytic hydrogen production. [ABSTRACT FROM AUTHOR]

Here, a metasurface‐based fiber‐to‐chip multiplexing coupler is presented that can realize flexible mode conversion and multiplexing coupling between few‐mode fibers and on‐chip single‐mode waveguides. The proposed approach makes use of the symmetrical characteristics of fiber eigenmodes and high freedom of light phase manipulation to obtain the functional phase distribution of metasurfaces. The use of cylindrical nanopillar as metasurface nanostructures ensures its polarization independent optical response. Several fiber‐to‐chip multiplexing couplers are demonstrated by using the angular spectrum methods and the finite‐difference time‐domain (FDTD) simulations. It is found that the two or three modes can be flexibly demultiplexed and then be coupled into the corresponding on‐chip waveguides with low crosstalk. Further, two possible fabrication schemes for multiplexing couplers are proposed and then the related fabrication tolerances and misalignment effects are evaluated and discussed. Compared with traditional on‐chip couplers, metasurface‐based couplers have advantages of ultracompact footprint and low crosstalk. Such study explores the application of metasurfaces in multiplexing coupling between few‐mode fiber and on‐chip single‐mode waveguides, which is expected to break through the bottleneck of current mode‐division multiplexing technologies in optical interconnection and meet the ever‐increasing demand for large data throughput of the photonic integrated chips. [ABSTRACT FROM AUTHOR]

Circularly polarized luminescent inorganics arouses attentions due to scalable preparation and versatile chiral optoelectronic applications. Here, strong circularly polarized luminescence (CPL) activity has been developed from self‐assembled cellulose nanocrystals decorated with blue emitting silicon quantum dots (QDs). The electrostatic attraction promotes the successful incorporation of QDs into chiral template matrix to form homogeneous hybrid nanoarchitecture films. It is found that their circular dichroism behaviors are closely related to the photonic band gap (PBG) while the CPL behaviors are determined by the QDs and PBG simultaneously. Furthermore, the as‐prepared chiral composite thin films have been employed as an efficient circularly polarized light source for preparing enantioselective polymer, which can induce chirality and photopolymerization simultaneously. Such strong CPL activity in nanoarchitecture films is highly promising for future inorganic optoelectronics. [ABSTRACT FROM AUTHOR]

The amplified spontaneous emissions in blue quantum dots (QDs) are still constrained by their high thresholds due to the challenge in engineering alloyed core–shell interface in the QDs with a wide bandgap to suppress Auger recombination. Compared with their red and green counterparts, the larger reactivity difference between the alloyed shell precursors makes it hard to regulate the composition and structure of the shell, and the smaller potential barrier between the core and the alloyed shell in blue QDs renders charge carriers tunneling into surface defects easier. Here, we employ a Lewis soft base ligand, 1‐decanethiol, to balance the mismatched reactivity between Zn and Cd precursors for crafting a thick gradient alloyed shell with gradually increased potential barrier, which can not only restrict the charge carriers tunneling but also smooth the confinement potential. As a result, the resulting blue QDs show a long Auger lifetime of 1.3 ns, and a low threshold of 6.9 µJ cm−2 excited by a femtosecond laser, which is the record value among all reported blue‐emitting nanocrystals and comparable to those of state‐of‐the‐art red and green QDs. [ABSTRACT FROM AUTHOR]

As a significant part in optical computation, analogue optical spatial/temporal differentiators could play a great role in all‐optical signal processing, feature extraction, and optical storage. In the past few years, they have experienced rapid development but mostly for a single function. For many scenarios, optical computation with integrated functionalities is highly desired. In this work, an analogue optical spatiotemporal differentiator utilizing all‐dielectric multilayer is proposed. The film stack is specifically engineered to satisfy the requirements for both spatial and temporal transfer functions of the ideal differentiator. The time‐space performance of the device is numerically examined from the output field profile of the classical Gaussian beam or pulse. A wavelength‐scale high resolution for edge detection is attained using the integrated differentiator. This work may pave a potential way to establish ultracompact, high‐bandwidth, and real‐time optical multiple functional computation systems. [ABSTRACT FROM AUTHOR]

Radar and sonar technologies are generally used to detect objects in air space and water. In some cases, both technologies are involved in probing waterborne objects like submarines. However, the simultaneous stealth regarding these two detection methods is not well explored due to the difficulty in satisfying material properties for two different physical systems. In this work, an artificial ultrathin amphibious stealth coat with a minimum thickness less than 0.5 mm achieving free‐space microwave and underwater acoustic absorption is proposed and demonstrated. It is realized by combining an electromagnetic metasurface and an acoustic metasurface—a flexible printed circuit with multisized metal resonators and a polydimethylsiloxane film with multisized air cavities. These two alien metasurfaces are engineered with minimized disturbance to each other by controlling the thicknesses of the resonators as thin as possible. A free‐space microwave absorptivity over 80% in the 12.38–13.7 GHz region and an underwater acoustic reflectance less than 10% in the 80–160 kHz region are obtained experimentally. The current work may shed light on advanced stealth technologies of the free‐space microwaves and underwater acoustic waves. [ABSTRACT FROM AUTHOR]

Analog spatial differentiator is an important optical computational device that can be potentially used in the field of high‐speed edge detection and optical image processing. In the current stage, a general method is still required to robustly design compact devices for various spectrum or complex situation. In this work, a dielectric metasurface method is proposed and experimentally demonstrated to build optical spatial differentiators. This is physically realized by a high‐quality magnetic resonance mode that is hybridized with the classic bounded surface wave via grating coupling. Experimentally, a well‐defined first‐order differentiation effect is observed at oblique light incidence. The application potential of this device is evaluated by inputting various figures. It is shown that it can perform an optical processor to trace the profiles of the figure content with a resolution better than 30.8 µm. This work may pave a robust way to build ultracompact optical computation devices for real‐time image processors, which can be freely extended to various frequencies. [ABSTRACT FROM AUTHOR]

Multiphoton excited fluorescence of organic molecules is promising in the applications of efficient nonlinear optical devices and bioimaging. However, they usually have disadvantages of poor photostability and serious fluorescence quenching in aqueous media or solid state, which seriously limit their related applications. In this work, for the first time, the two‐photon excited Förster resonance energy transfer (FRET) process is used to enhance the solid‐state fluorescence of the supramolecular centre (acceptor) in an artificial 3D metal–organic complex (MLC), in which a 3D Zn (II)‐coordinated tetrahedral core is utilized as the donor. More interestingly, the two‐photon light harvesting system, which can be pumped with an optical intensity as low as 1 MW/cm2, exhibits an ultrafast energy transfer rate (∼6.9 × 108 s−1) and ultrahigh photostability. The underlying physical mechanisms are revealed through comprehensive steady‐state and time‐resolved spectroscopic analysis. This work demonstrates that the 3D MLC can be directly used in two‐photon bioimaging and also sheds light on developing other multiphoton harvesting systems, such as metal–organic frameworks. [ABSTRACT FROM AUTHOR]

2D layered halide perovskites have attracted significant attention. Apart from the linear optical properties, it is also intriguing to explore the nonlinear optics of 2D layered halide perovskites and their heterostructures. Previous nonlinear optical (NLO) studies of 2D perovskites primarily focus on the thin films or microplates. Herein, the NLO properties of (n‐C4H9NH3)2PbI4/(n‐C4H9NH3)2(CH3NH3)Pb2I7 heterostructures with centimeter size are systematically studied. The NLO properties can be continuously tuned by changing the thickness. A giant two‐photon absorption (2PA) coefficient up to 44 cm MW−1 is obtained for the heterostructures with a total thickness of 20 µm based on the nonlinear transmittance measurement. Additionally, strong multiphoton‐induced photoluminescence is observed in the heterostructures. It is proposed that the giant 2PA coefficient might arise from the small thickness (≈1 µm) of (n‐C4H9NH3)2(CH3NH3)Pb2I7 layer and possibly the nonradiative energy transfer between the different constituting layers within the heterostructures through an antenna‐like effect. Finally, benefiting from the giant 2PA coefficient, direct detection of 980 nm light is demonstrated with a responsivity of 10−7 A W−1 in the heterostructures. The findings suggest the promising applications of 2D perovskite heterostructures in the infrared photodetection and some other nonlinear absorption related optoelectronic devices. [ABSTRACT FROM AUTHOR]