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

Abstract

Sb3+- and Bi3+-doped Cs2SnCl6 zero-dimensional perovskites are emerging as stable and nontoxic phosphors for light emitting diodes. The outermost s-electrons (ns2) of the dopants are responsible for both light absorption (ns2 to ns1np1) and emission (ns1np1 to ns2). 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 ns1np1 is a triplet state 3T1u *. The notation “*” implies spin–orbit coupling between the 3T1u and 1T1u states. After light absorption, 3T1u * 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 3T1u *, 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 3T1u * and, therefore, a single emission peak.

Dual‐Band‐Tunable White‐Light Emission from Bi3+/Te4+ Emitters in Perovskite‐Derivative Cs2SnCl6 Microcrystals

“…Upon Bi 3+ doping, additional absorption bands at 324, 347, and 372 nm were observed, accompanied by the enhanced intensities as the Bi 3+ concentration increased, indicating that these absorption bands were associated with the Bi 3+ ‐related centers. The absorption band at 372 nm was also observed in Cs 2 SnCl 6 : Bi 3+ crystals as previously reported by Tang and Nag et al [7a, 11] . Tang et al.…”

“…Instead, Nag et al. attributed the 372 nm absorption band to the A‐band absorption, namely, the spin‐orbital allowed 1 S 0 ( 1 A 1g )→ 3 P 1 ( 3 T 1u ) transition of Bi 3+ ion, [11] which, however, is neither reasonable as it did not match with the PL excitation band of the MCs. Actually, the 372 nm absorption band contributed merely a little to the PL emission, as visualized by the deconvolution of the PL excitation spectrum (Figure S11).…”

Sb3+–Er3+‐Codoped Cs2NaInCl6 for Emitting Blue and Short‐Wave Infrared Radiation

“…The new absorptions are attributed to 5 s 2 5 s 1 p 1 transitions of Sb 3+ . The ground state (5 s 2 ) is and the excited states (corresponding to 5 s 1 p 1 ) are , , and ; “*” indicates spin‐orbit coupling between the and excited states which is significant for Sb 3+ ions with high atomic number [6c, 17, 18] . is a forbidden transition.…”

Colloidal Sb3+-Doped Cs2InCl5·H2O Perovskite Nanocrystals with Temperature-Dependent Luminescence

“…The new PL and PLE peaks obtained after Sb 3+ doping might be attributed to the 5s 2 electrons of the dopant. Absorption of light by Sb 3+ -doped metal halides can excite a 5s 2 electron ( 1 S 0 state) yielding a configuration of 5s 1 p 1 that can have four states of 1 P 1 and 3 P n ( n = 0, 1, 2). − There is spin–orbit coupling between 3 P 1 and 1 P 1 states, and therefore, these states are presented as 3 P 1 * and 1 P 1 * , respectively. The excitation from 1 S 0 to 3 P 1 * becomes partially allowed because of the spin–orbit coupling and is the lowest energy absorption for Sb 3+ dopants.…”