Origin of Luminescence in Sb3+- and Bi3+-Doped Cs2SnCl6 Perovskites: Excited State Relaxation and Spin-Orbit Coupling

Sb3+- and Bi3+-doped Cs2SnCl6 zero-dimensional perovskites are emerging as stable and nontoxic phosphors for light emitting diodes. The outermost s-electrons (ns(2)) of the dopants are responsible for both light absorption (ns(2) to ns(1)np(1)) and emission (ns(1)np(1) to ns(2)). At cryogenic temperatures, the Sb3+ dopant shows two emission peaks, but Bi3+ shows only one emission peak. Why? Here we address such questions, revealing the origin of luminescence in Sb3+- and Bi3+-doped Cs2SnCl6. We find that the emitting excited state ns(1)np(1) is a triplet state T-3(1u)*. The notation * implies spin-orbit coupling between the T-3(1u) and T-1(1u) states. After light absorption, T-3(1u)* is occupied with one electron, which then undergoes Jahn-Teller distortion yielding a relaxed excited state (RES). For the Sb3+ dopant, the combination of Jahn-Teller distortion and spin-orbit coupling gives rise to two minima in RES T-3(1u)*, resulting in two emission peaks, whereas for the Bi3+ dopant, the spin-orbit coupling significantly dominates over the Jahn-Teller splitting yielding a single minimum in RES T-3(1u)* and, therefore, a single emission peak.

Automated summary

Sb3+ and Bi3+ doped Cs2SnCl6 zero-dimensional perovskites are stable and nontoxic phosphors for LEDs. The luminescence originates from the spin-orbit coupling of the s-electrons of the dopants and the ns(1)np(1) excited state. The different number of emission peaks in Sb3+ and Bi3+ doping is due to the interplay between Jahn-Teller distortion and spin-orbit coupling.