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Design and exploration of high-performance nonlinear optical (NLO) materials have long been sought with the goal of tunable local structures and NLO properties for advanced laser technology. Thus far, the design strategies for second-order NLO materials have been mainly focused on anionic groups that have made great progress in the development of new NLO compounds. However, few studies have focused on the effects of cationic components and their contributions to NLO properties have long been underappreciated and remain unclear. Here, by introducing pressure to continuously tune the Cu displacement, we demonstrate the significant role of the cationic configuration in NLO properties, and a remarkable enhancement by one order of magnitude in second-harmonic generation (SHG) has been achieved at 3.4 GPa in thiophosphate CuInP 2 S 6 (CIPS). In situ high-pressure structural characterization indicates that Cu cations move from the van der Waals edge to the cages of S 6 octahedra during compression and subsequently form highly distorted [CuS 6 ] octahedra at 3.2 GPa. We quantitively demonstrate the contributions of cationic displacement on the octahedral distortion and interband dipole moments, which dominate optical nonlinearity and determine the enhanced SHG. This work deepens the fundamental understanding of the relationship between cationic displacement and SHG properties, thus providing new paths to NLO material design by optimizing the cationic configurations.

Direct neutron detection based on semiconductor crystals holds promise to transform current neutron detector technologies and further boosts their widespread applications. It is, however, long impeded by the dearth of suitable materials in the form of sizeable bulk crystals. Here, high‐quality centimeter‐sized LiInP2Se6 single crystals are developed using the Bridgman method and their structure and property characteristics are systematically investigated. The prototype detectors fabricated from the crystals demonstrate an energy resolution of 53.7% in response to α‐particles generated from an 241Am source and robust, well‐defined response spectra to thermal neutrons that exhibit no polarization or degradation effects under prolonged neutron/γ‐ray irradiation. The primary mechanisms of Se‐vacancy and InLi antisite defects in the carrier trapping process are also identified. Such insights are critical for further enhancing the energy resolution of LiInP2Se6 bulk crystals toward the intrinsic level (≈8.6% as indicated by the chemical vapor transport‐grown thin crystals). These results pave the way for practically adopting LiInP2Se6 single crystals in new‐generation solid‐state neutron detectors.