Enhanced Extrinsic Self‐Trapped Exciton Photoluminescence for Highly Linearly Polarized Emission in Thin Layered Er:In ₂ P ₃ S ₉

ABSTRACT Recently, self‐trapped excitons (STEs) emission has attracted worldwide attention due to its broadband and high photoluminescence quantum yield. Compared with the prevailing STEs in halides, there is little report on the STEs emission in thiophosphates, and their PLQY is relatively low. This paper reports the enhanced extrinsic STEs and thickness‐tunable linear polarized emission in Er:In 2 P 3 S 9 . The absorption of the defect state that contributes to the formation of STEs greatly enhances after Er doping. PL spectra reveal that Er doping can dramatically improve the extrinsic STEs emission intensity by two orders of magnitude. Temperature‐dependent PL demonstrates the higher Huang‐Rhys factor, larger exciton binding energy, stronger electron‐phonon interaction, and increased radiation recombination rate in Er:In 2 P 3 S 9 . Moreover, the Er:In 2 P 3 S 9 exhibits a thickness‐tunable linear polarized emission. When the thickness is reduced to 12 nm, the degree of polarization (DOP) up to 0.48 is obtained. Angle‐resolved polarized Raman spectroscopy and the thickness‐dependent behavior verify there is are remarkable anisotropy of lattice vibration and electron‐phonon interaction, which makes a significant contribution to the linear polarized emission and thin‐layer induced DOP improvement. This work provides an effective doping strategy to enhance the extrinsic STEs emission and extend the potential polarized nanophotonics application of layered thiophosphates.