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A series of Mn2+-doped CsPbCl3 nanocrystals (NCs) was synthesized using reaction temperature and precursor concentration to tune Mn2+ concentrations up to 14%, and then studied using variable-temperature photoluminescence (PL) spectroscopy. All doped NCs show Mn2+ 4T1g → 6A1g d–d luminescence within the optical gap coexisting with excitonic luminescence at the NC absorption edge. Room-temperature Mn2+ PL quantum yields increase with increased doping, reaching ∼60% at ∼3 ± 1% Mn2+ before decreasing at higher concentrations. The low-doping regime is characterized by single-exponential PL decay with a concentration-independent lifetime of 1.8 ms, reflecting efficient luminescence of isolated Mn2+. At elevated doping, the decay is shorter, multiexponential, and concentration-dependent, reflecting the introduction of Mn2+–Mn2+ dimers and energy migration to traps. A large, anomalous decrease in Mn2+ PL intensity is observed with decreasing temperature, stemming from the strongly temperature-dependent exciton lifetime and slow exciton-to-Mn2+ energy transfer, which combine to give a strongly temperature-dependent branching ratio for Mn2+ sensitization.
Yuan et al. (Fri,) studied this question.