Brillouin Light Scattering of Halide Double Perovskite

Cs 2 Ag 1− x Na In y Bi Cl 6 with high photoluminescence quantum yield (PLQY) and broadband emission due to self‐trapped excitons (STEs) is one of the promising candidates for single‐emitter‐based white light–emitting materials devices. Considering fundamental physical mechanisms, structure design performance optimization devices, comprehensive knowledge elasticity, thermal properties are imperative understand formation STEs in minimize thermomechanical stresses induced device failure, respectively. However, its elastic still poorly understood. Herein, first angle‐resolved Brillouin light scattering (BLS) measurements study a bulk 0.4 0.6 InCl :0.04%Bi 3+ crystal reported, first‐principles calculations phonon dispersions used further validate our experimental results. Using measured frequency shifts, we evaluate low elasticity : C 11 = 38.63, 12 16.11, 44 10.20 GPa, which supports thesis that exist semiconductors soft lattice. Additionally, an ultralow‐acoustic Debye temperature (87 K) lattice conductivity (1.03 W m −1 K ) along [111] direction , indicates weak interatomic interactions estimated. Furthermore, general approach also provided investigate different structures utilizing BLS spectroscopy.