Understanding photoluminescence of Cs2ZrCl6 doped with post-transition-metal ions using first-principles calculations

Doped lead-free halide perovskites have been widely reported for impressive photoluminescence properties. Herein we study the mechanisms of photoluminescence in Se4+-, Te4+-, Sb3+-, and Bi3+-doped Cs2ZrCl6 and also in this undoped host via first-principles calculations with hybrid density functionals. The results show that the main photoluminescence in the host, as well as isovalent and aliovalent dopants, can be attributed to highly localized self-trapped excitons composed of an electron on Zr and a Vk center (molecular-like Cl2-), MCl6 (M=Se4+,Te4+), and MCl5 (M=Bi3+,Sb3+) complexes, respectively. The systematic underestimation of the emission energies is discussed and is attributed to the over-relaxation of the excited-state geometric structures. Our results illustrate the photoluminescence processes and excited-state dynamics in host and aliovalent dopant of Cs2ZrCl6, which may inspire further revelations of the mechanisms of photoluminescence of other materials in the tetravalent halide perovskite family.