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 ${\mathrm{Se}}^{4+}$-, ${\mathrm{Te}}^{4+}$-, ${\mathrm{Sb}}^{3+}$-, and ${\mathrm{Bi}}^{3+}$-doped ${\mathrm{Cs}}_{2}{\mathrm{ZrCl}}_{6}$ 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 ${V}_{k}$ center (molecular-like ${\mathrm{Cl}}_{2}^{\ensuremath{-}}$), $M{\mathrm{Cl}}_{6}$ ($M=\phantom{\rule{0.28em}{0ex}}{\mathrm{Se}}^{4+},{\mathrm{Te}}^{4+}$), and $M{\mathrm{Cl}}_{5}$ ($M=\phantom{\rule{0.28em}{0ex}}{\mathrm{Bi}}^{3+},{\mathrm{Sb}}^{3+}$) 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 ${\mathrm{Cs}}_{2}{\mathrm{ZrCl}}_{6}$, which may inspire further revelations of the mechanisms of photoluminescence of other materials in the tetravalent halide perovskite family.