Enhancing thePhotoexcited Carrier Spin RelaxationLifetime in CsPbBr₃ Perovskite Quantum Dots by ²⁰⁸Pb Isotope Enrichment

CsPbBr₃ perovskite quantum dot (PQD) films enriched with ²⁰⁸Pb (<i>I</i> = 0) or ²⁰⁷Pb (<i>I</i> = 1/2) isotope were used to study the effect of nuclear spin on the photoexcited carrier spin relaxation using circularly polarized femtosecond transient absorption spectroscopy at 293 and 77 K. At 293 K, the short carrier spin relaxation lifetimes of ²⁰⁸Pb-enriched PQDs (2.0 ps) and ^natPb PQDs (0.70 ps) indicate that electron–phonon interactions dominate. At 77 K, the ²⁰⁷Pb-enriched PQD carrier spin relaxation lifetime was not detectible within the instrumental limit (<0.30 ps). However, the carrier spin relaxation lifetime increased to 5.0 ps for ^natPb PQDs and 170 ps for ²⁰⁸Pb-enriched PQDs. The dramatic increase in the ²⁰⁸Pb-enriched PQD carrier spin relaxation lifetime suggests that decreasing the concentration of ²⁰⁷Pb in the PQDs can reduce spin decoherence from nuclear spin–carrier spin coupling and enhance the lifetime.