Polarized Photoluminescence and Raman Spectra of a Lead-Free 1D CsCu₂I₃ Single Crystal

Lead-free CsCu₂I₃ perovskites are promising luminescent materials with strong optical performance and environmental stability, but the fundamental origins of their emission polarization remain unclear, particularly whether the intrinsic polarization of self-trapped excitons (STEs) can be maintained. Here, we systematically present the photophysical properties of high-quality CsCu₂I₃ single crystals. Temperature-dependent photoluminescence reveals broadband emission from STEs with strong electron-phonon coupling (γ_LO ≈ 120 meV) and a negative thermal quenching behavior (activation energy of ∼77.5 meV) due to shallow trap states. Crucially, polarized photoluminescence experiments unambiguously demonstrate that the linear polarization (∼14.3% at 80 K) arises specifically from anisotropic absorption and not intrinsic STE emission polarization. Furthermore, angle-dependent Raman spectroscopy demonstrates strong anisotropy, evidenced by the intensity variation across different polarization directions, consistent with the anisotropic absorption behavior of the material. These findings clarify the photophysical origin of emission anisotropy in CsCu₂I₃ and highlight its potential for polarization-related optoelectronic applications.