Near‐Unity Linear Polarization of Self‐Trapped Exciton Emission in Cu 3 PS 4 With Highly Anti‐Thermal‐Quenching for Sensitive Optical Thermometry

ABSTRACT Recently, self‐trapped exciton (STE) emission has attracted considerable attention. However, reports on the STE emission in transition‐metal phosphorus chalcogenides remain scarce, and their interesting luminescence and underlying photo‐physical mechanism aren't yet fully revealed. Herein, we reveal the near‐unity linearly polarized STE emission in Cu 3 PS 4 along with its intriguing anti‐thermal‐quenching luminescence and optical thermometry. The Cu 3 PS 4 show two broadband emissions with full‐width at half‐maximum of ∼200 nm and large Stokes shifts of 0.63/1.03 eV. Both temperature‐dependent photoluminescence and transient absorption spectroscopy (TAS) confirm that inherent lattice distortion, large exciton binding energy, and strong electron‐phonon interaction underlie the emission of Cu 3 PS 4 , validating unambiguously their STE origin. Remarkably, Cu 3 PS 4 demonstrates an interesting anti‐thermal‐quenching emission and optical thermometry. The quenching threshold temperature and thermometry relative sensitivity are as high as 400 K and 2.01% K −1 , respectively. Moreover, Cu 3 PS 4 exhibits a near‐unity linearly polarized STE emission with degree of polarization up to 0.93. According to the TAS and angle‐resolved polarized Raman spectroscopy, it is rational to assign that the anisotropic optical absorption and electron‐phonon interaction predominantly contribute to this exceptional linear polarization emission. These findings elucidate the STE emission of Cu 3 PS 4 and establish its promising applications in broadband optical polarizers and high‐power light‐emitting diodes.