Deep-Red-Emissive Organic–Inorganic Hybrid Crystal with Multifunctional Nonlinear Optical Responses

Abstract Red-emissive nonlinear optical (NLO) crystals hold considerable promise for deep-tissue detection, low-scattering imaging, frequency conversion, and integrated photonics. However, it remains highly challenging to simultaneously achieve stable red emission, pronounced NLO responses, and structural robustness within a crystalline material. In this work, we report a new organic–inorganic hybrid deep-red-emissive crystal, (4-(4-dimethylaminostyryl)-1-methylpyridinium)PbI3 (DAPbI), constructed via a room-temperature solvent evaporation method. Benefiting from the cooperative regulation of the highly polarizable DA+ chromophore and the rigid, locally distorted Pb–I framework, DAPbI exhibits complementary linear and NLO responses. Efficient deep-red emission (∼680 nm) is observed at room temperature with a photoluminescence quantum yield of 21.12%. Under near-infrared excitation (800–1300 nm), DAPbI exhibits distinct two-photon-excited fluorescence (TPEF), with a two-photon action cross-section up to 153 times that of Rhodamine B. In addition, tunable second-harmonic generation (SHG) is achieved, with intensities up to 1.5-fold relative to a potassium dihydrogen phosphate (KDP) reference. These results demonstrate that DAPbI is a multifunctional hybrid NLO crystal integrating deep-red emission, TPEF, and SHG, thereby providing a new strategy for the design of organic–inorganic NLO materials.