Rationalizing the Photoluminescence of Bi³⁺and Sb³⁺in Double Perovskite Halide Crystals

Bi- and Sb-doped halide perovskites have been widely reported for their high absorption coefficients, bright emission, and impressive photoluminescence quantum yields. However, several different transition processes can be involved and the mechanisms have not been well understood. We present first-principles calculations with hybrid density functionals on a variety of representative Bi- and Sb-doped chloride systems to resolve these problems and rationalize behaviors. The results show that excitation and emission energies are well predicted in general, and the latter shows a good correlation with the metal-Cl bond length in the host. The remarkably different manifestations of Sb³⁺and Bi³⁺in hosts with In and Ag and the emission energies are predicted and well interpreted with calculated relaxation processes. Negatively charged neighboring cation-vacancy compensators greatly uplift defect levels but reducesp→s²emission energies. In contrast, a positively charged neighboring anion vacancy downshifts the defect levels and reduces thesp→s²emission energies in both Bi³⁺and Sb³⁺. The results obtained provide a significant insight in understanding the photoluminescence processes and excited-state dynamics of chloride double perovskites activated by Bi³⁺and Sb³⁺, as well as rock-salt and K₂PtCl₆-type systems, and inspire the revelation of the mechanisms of other luminescent materials containing ions with a lonens²pair.