Extrinsic Dual‐Mode Self‐Trapped Excitons Emission With Highly Linear Polarization From Cu₃PS₃Se

Abstract Benefiting from the potential application as a single component white light source, the broadband self‐trapped excitons (STEs) emission in low‐dimensional metal halides has attracted wide attention. However, such broadband STE emission in metal thio‐ and seleno‐phosphates is scarce, and the formation mechanism is ambiguous. Herein, the broadband dual‐mode (red and near‐infrared) light emission and their linear polarization in orthorhombic Cu₃PS₃Se crystals are reported. The absorption and photoluminescence (PL) spectra show a large Stokes shift of 0.43/0.76 eV and a broad emission wavelength range of ≈200 nm, exhibiting the significant STEs feature. Transient absorption spectroscopy (TAS) reveals a broad positive photo‐induced absorption, further proving the formation of STE states. These STEs exhibit a highly linear polarized emission behavior with a degree of polarization up to 0.51. According to the excitation angles dependent polarized PL and Raman spectroscopy measurements, it is assigned that both the anisotropic optical absorption and electron‐phonon interaction contribute to the STEs emission polarization in Cu₃PS₃Se. These findings not only extend the STEs from metal halides to metal thio/seleno‐phosphates but also offer the potential prospects for novel optical polarizers, polarization‐sensitive photodetectors, optical and optoelectronic synaptic devices application of anisotropic STEs emission.