Efficient second-order nonlinear response and upconversion emission from a wide-bandgap quasi-1D lead bromide perovskite

Low-dimensional hybrid organic-inorganic perovskites (HOIPs) have attracted significant attention for applications such as solar cells, light-emitting diodes, and photodetectors. Compared with their three-dimensional counterparts, low-dimensional perovskites (LDPs) exhibit prominent characteristics such as stronger quantum confinement, remarkable exciton effects, and structural diversity, which are crucial for their nonlinear optical (NLO) properties. However, it remains hard to obtain ideal perovskite crystals with high optical transparency, large NLO responses, and excellent stability simultaneously, which are highly desirable for next-generation integrated photonics. In this work, a wide bandgap (4.2 eV) quasi-1D perovskite single crystal, PEA₃PbBr₅·H₂O, with a considerable second-order NLO coefficient (0.1 pm V⁻¹) that is 1/4 times that of the commercial crystal KH₂PO₄ (KDP), is reported. Power-, wavelength-, and polarization-dependent experiments are implemented, unfolding a high polarization ratio of up to 94%. Moreover, an unexpectedly anomalous green PL phenomenon from the single crystal is discovered. The upconversion emission in the crystal, as well as the time-resolved photoluminescence dynamics, is also investigated. Such a quasi-1D perovskite may provide a new platform for advancing the application of nonlinear optics.