Dopant-Induced Slow Spin Relaxation in CsPbBr₃ Perovskite Nanocrystals

Lead halide perovskites comprise a class of materials holding great promise for spin-related applications due to their strong spin–orbital coupling (SOC) effect. However, the strong SOC also shortens the lifetime of spin states and thus limits their further application. Herein we take Bi-doped CsPbBr3 perovskite nanocrystals (NCs) as an example material to study how metal doping can affect the spin-relaxation process, by using circularly polarized transient absorption (TA) spectroscopy. We demonstrate that in undoped CsPbBr3 NCs the spin relaxation is governed by the electron–hole exchange (EHE) mechanism and in doped NCs the Bi-dopants significantly slow down the spin relaxation by creating an ultrafast (∼0.13 ps) hole trapping process and thus disturbing the EHE spin de-coherent process. By tuning the Bi-doping ratio, the spin-relaxation time in doped NCs is prolonged to ∼24.6 ps, much longer than that (∼4.4 ps) in undoped NCs. Our finding suggests that doping a metal element is an effective way to tune the spin relaxation in perovskites NCs and likely also in many other types of quantum-confined NCs.