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Mid‐infrared (MIR) lasers generated by nonlinear optical (NLO) crystals have aroused extensive attention in various military and civilian applications. Among the MIR NLO crystal family, LiInSe2 (LISe) is a promising candidate in the generation of MIR lasers due to its wide transmission range, large bandgap, and high laser‐induced damage threshold. However, the intrinsic defects in LISe induce optical losses, which will induce laser damage and hinder the performance of MIR laser generation. In this work, the mechanism of optical absorption induced by defects is revealed in LISe through transient absorption (TA) spectroscopy. It is verified that the deep‐level defects in LISe give rise to the extra optical absorption, which is owing to the excited state absorption (ESA) and photo‐induced absorption (PIA). Accordingly, for improving the optical properties of LISe crystals, Li2Se vapor‐mediated annealing to reduce defects concentration is rationally designed. The results confirmed that the optical properties of annealed LISe are improved due to the decrease of defects concentration. Ultimately, the performance of MIR laser generation is successfully enhanced by using the annealed LISe crystal. This work provides deep insights into the defect‐induced absorption losses in LISe crystals and promotes the application of LISe crystals in MIR laser generation. [ABSTRACT FROM AUTHOR]

Abstract LiInSe2 crystals are promising semiconductor materials for neutron detectors due to the large neutron capture cross-sectional area of the specific isotopes (6Li) and high charge transport properties. However, the optoelectronic performance fails to reach the expected level due to the difficulty of controlling the crystal defects. Herein, we modulate the stoichiometric ratio to control the type of defects in single LiInSe2 crystals grown by the vertical Bridgman method. The UV‒vis–NIR transmission results indicate that the band gap of the yellow colored Li1.01In1Se2 sample is close to ~ 2.83 eV at room temperature, and this value is consistent with the theoretical band gap of LiInSe2 (~ 2.86 eV). Photoluminescence (PL) spectroscopy was used to analyze the defect concentration. The results indicate that the defect types in the yellow Li1.01In1Se2 single crystal are VSe + and LiIn 2−; these result from the introduction of excess Li and the suppression of the adverse defects in InLi 2+ and VLi −. These results demonstrate a feasible route for obtaining high-quality yellow 6LiInSe2 crystals and promote the application of 6LiInSe2 neutron detectors.

Optical quality cm-sized LiInSe2 crystals were grown using the Bridgman–Stockbarger method, starting from pure element reagents, under the conditions of a low temperature gradient of 5–6 degrees/cm and a slight melt overheating. The phase purity of the grown crystal was verified by the powder XRD analysis. The thermophysical characteristics of LiInSe2 were determined by the XRD measurements in the temperature range of 303–703 K and strong anisotropy of the thermal expansion coefficients was established. The following values of thermal expansion coefficients were determined in LiInSe2: αa = 8.1 (1), αb = 16.1 (2) and αc = 5.64 (6) MK−1. The electronic structure of LiInSe2 was measured by X-ray photoelectron spectroscopy. The band structure of LiInSe2 was calculated by ab initio methods. [ABSTRACT FROM AUTHOR]

Optical quality cm-sized LiInSe2 crystals were grown using the Bridgman–Stockbarger method, starting from pure element reagents, under the conditions of a low temperature gradient of 5–6 degrees/cm and a slight melt overheating. The phase purity of the grown crystal was verified by the powder XRD analysis. The thermophysical characteristics of LiInSe2 were determined by the XRD measurements in the temperature range of 303–703 K and strong anisotropy of the thermal expansion coefficients was established. The following values of thermal expansion coefficients were determined in LiInSe2: αa = 8.1 (1), αb = 16.1 (2) and αc = 5.64 (6) MK−1. The electronic structure of LiInSe2 was measured by X-ray photoelectron spectroscopy. The band structure of LiInSe2 was calculated by ab initio methods.

Lithium indium selenide (LiInSe2) is being developed for use as a room temperature semiconductor detector for thermal neutrons. The material has been studied for a number of applications including non-linear optics such as parametric oscillators, as anode material for lithium ion batteries, piezoelectrics, as a scintillation detector material, and as a semiconductor detector material. The recent advances of the crystal growth, material processing, and detector fabrication have led to semiconductor neutron detectors with up to 100 mm2 active area. The theoretical thermal neutron detection sensitivity and gamma rejection ratio (GRR) are comparable to 10 atm, 3He tubes of similar size. Detector fabrication and characterization are described and the results are discussed.

Owing to their relatively high electronic conductivity and electrochemical activity, bimetallic chalcogenides exhibit promising applications in advanced lithium-ion batteries. Herein, for the first time, a uniform thin carbon layer (about 2-3 nm) derived from citric acid coating bimetallic selenide, LiInSe2, is designed. When used as an anode material for lithium-ion batteries, the novel carbon-coated LiInSe2 anode delivers high initial charge/discharge capacities of 545.2/732.0 mAhg-1 at a current density of 100 mAg-1. Even after 800 cycles at 1500 mAg-1, a high reversible capacity of 333 mAhg-1 can be achieved, suggesting its superior rate capability and cycling stability. The excellent electrochemical performance of the carbon-coated LiInSe2 anode is ascribed to the improved electronic/ionic conductivity, electrochemical activity, and reaction kinetics. This remarkable lithium storage property indicates the potential application of bimetallic selenide for future lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The electronic structure and optical properties of the LiIn1- xGa xSe2 ( x = 0, 0.25, 0.5, 0.75, 1) solid solution were studied by density functional theory (DFT) with pure functionals. The exchange-correlation is treated within the local density approximation (LDA) and generalized-gradient approximation (GGA). The electronic structures for each respective compound are discussed in detail. Calculations reveal that gallium incorporation can be used to tune the optical-electrical properties of the solid solution and correlates with the lattice parameter. The band gap trend of the LiIn1- xGa xSe2 system follows a nonlinear behavior between the LiInSe2 and LiGaSe2 ternary boundaries. The bowing parameter is estimated to be on the order of 0.1-0.3 eV at the Γ-point. Low-temperature optical absorption revealed a 30% change in the temperature dependence of the band gap for the intermediate compound LiIn0.6Ga0.4Se2 compared to ternary boundaries and suggests the heat capacity to be another control element through strain. [ABSTRACT FROM AUTHOR]

• High-quality LiInSe 2 crystals (φ26 mm) were obtained by optimized Bridgman method. • Defects of In Li , V Li and V Se in LiInSe 2 are verified by spectroscopy. • The defect concentration was reduced greatly by annealing under Li 2 Se vapor. Mid-infrared (MIR) lasers based on nonlinear frequency conversion by nonlinear optical (NLO) crystals are urgently desired for various military and civilian applications. LiInSe 2 (LISe) crystal has aroused intense attention due to its remarkable optical properties. However, the presence of point defects in LISe increases absorption loss and degrades the laser damage threshold (LDT), which limits the practical application in high-power MIR lasers. Therefore, it is essential to reveal the defect types and their formation mechanism in LISe, which is beneficial to design a rational strategy to improve the crystal quality. Here, large-sized LISe crystals with a diameter of 26 mm were successfully grown by the optimized Bridgman method using oriented seed crystal. Furthermore, three types of defects, V Se , V Li , and In Li in the as-grown LISe crystals were verified by photoluminescence (PL) spectra. Therefore, we designed the thermal annealing process under Li 2 Se vapor to compensate for the losses of Li and Se elements and reduce the defect concentration in LISe. Moreover, the evolution of defects in LISe crystals was determined by X-ray photoelectron spectroscopy (XPS), PL and ultrafast transient absorption spectra (TAS). All the experimental results confirm that the defect concentration in LISe greatly decreases and the crystal quality was obviously improved after annealing under Li 2 Se vapor. More importantly, this work provides a general strategy to reveal the defects in crystals and to improve the crystal quality of MIR chalcogenides for practical applications. [ABSTRACT FROM AUTHOR]

Evaporation and compositional changes of the liquids above the melting point of LiInSe2 crystals have been characterized quantitatively by using special techniques of a rapid thermal analysis and differential dissolution. The occurrence of a liquid immiscible region in the Li2Se-rich side of the Li2Se-In2Se3 diagram and incongruent evaporation with the preferential evaporation of In2Se3 rising markedly above boiling point were determined from the peaks on the thermal curves and from precise control over the composition of the vapour and residual solid as a function of temperature. It was shown that both the processes could be the sources of nonstoichiometry and inhomogeneity of the LiInSe2 crystals. [ABSTRACT FROM AUTHOR]

Fast neutron imaging is a powerful tool to investigate elemental/isotopic compositions of objects, supporting both scientific studies as well as cargo scanning. Current neutron imaging systems are faced with challenges associated with timing, detection efficiency, and/or spatial resolution. Here, we report on the use of a semiconducting lithium indium diselenide neutron sensor coupled to a Timepix ASIC for fast neutron imaging. Using a 15 cm thick copper knife edge, the spatial resolution of the neutron imager was found to be 1.55 mm for 9 MeV neutrons. The experimental detection efficiency at 9 MeV was in general agreement with calculations. [ABSTRACT FROM AUTHOR]

The Majorana nature of neutrinos is one of the most important questions being pursued in physics today. This has given the search for neutrinoless double-beta decay (0 ν β β) a high priority among proposed nuclear physics experiments. In this work, the objective was to evaluate several crystal compositions for possible use as a scintillating bolometer in 0 ν β β research. A crucial characteristic of the investigated crystals is that their compositions must include one of the few elements known to decay with double-beta emission. Therefore, we grew crystals containing molybdenum or selenium as a major constituent. Results are presented here for single-crystals of sodium molybdate and lithium indium diselenide. Scintillating bolometer data were measured at milli-Kelvin temperature and show good discrimination between alpha and beta/gamma emissions, which is crucial for background reduction. The lithium indium diselenide crystal was also used to measure the energy spectrum for the beta emission of indium decay, the first time a beta decay spectrum has been measured from self-emission in a scintillating bolometer. • Na 2 Mo 2 O 7 and LiInSe 2 crystals show promise as scintillating bolometers. • Na 2 Mo 2 O 7 and LiInSe 2 scintillating bolometers exhibit particle discrimination. • Beta decay spectrum of 115 In was measured in a ►LiInSe 2 scintillating bolometer. [ABSTRACT FROM AUTHOR]

Due to high density of 6Li isotope and the ability to respond to ionizing radiation through direct charge carrier transport, Li-containing chalcogenides are expected to be the replacement of 3He-tube or neutron reactive material coated semiconductor films for thermal neutron detection. However, the neutron detection efficiency of 6LiInSe 2 is limited to 82% ascribed to that 115In isotope captures neutrons and generates gamma rays, which deteriorated the neutron response. Neutron detection efficiency could be improved by gallium substitution since its low neutron capture cross-section. In this work, the electron and hole mobility (μ) of LiIn 1 − x Ga x Se 2 (x = 0, 0.25, 0.5, 0.75, 1) were studied by first-principles density functional theory (DFT) calculation, which demonstrated the electron mobility (μ e) of LiIn 0.5 Ga 0.5 Se 2 is close to that of LiInSe 2 while the hole mobility (μ h) is much improved. To further certify, both LiIn 0.5 Ga 0.5 Se 2 and LiInSe 2 crystals were grown under similar condition by vertical Bridgman method, exhibited comparable bandgap and bulk resistivity at room temperature. The charge transport behaviors were evaluated under 241Am@5.48MeV alpha particles. The full energy peak is clearly resolved in the pulse height spectra. The electron and hole mobility-lifetime products of LiIn 0.5 Ga 0.5 Se 2 are 1.5 × 10−5 cm2/V and 6.9 × 1 0 − 5 cm2/V, respectively. The resulting μ e of LiIn 0.5 Ga 0.5 Se 2 and LiInSe 2 crystals are 270 cm2V−1s−1 and 180 cm2V−1s−1, respectively, fitted by time of flight (TOF) technique. In addition, the μ h of LiIn 0.5 Ga 0.5 Se 2 is obtained with the value of 110 cm2V−1s−1, but the hole response is too weak to be resolved for LiInSe 2. [ABSTRACT FROM AUTHOR]