Sn2+ doping-induced large extra vibrational energy of an excited state for efficient blue emission in Cs2SnCl6:Bi

Luminescent metal halides doped with ns2-metal ions, such as 6s2-metal Bi3+, show excellent optoelectronic properties. However, the origin of the high photoluminescence quantum yield (PLQY) of Cs2SnCl6:Bi remains controversial and unclear. In this study, a series of Cs2SnCl6:Bi were synthesized by adopting different tin precursors of SnCl2/SnCl4. The samples from SnCl2 exhibited much higher PLQY than those from SnCl4, and the doping concentrations of Bi3+ had little effect on the high PLQY. When H3PO2 is added to the precursor of SnCl4 to reduce Sn4+ to Sn2+, the prepared Cs2SnCl6:Bi shows bright emission light and high PLQY. The high PLQY of Cs2SnCl6:Bi is attributed to the co-doping of Bi3+ and Sn2+. [SnCl4]2− and two VCl induce a large extra vibrational energy of the heavy localized excitons from [BiCl5]2− to enhance the efficiency of radiative recombination for high PLQY. This work deepens the understanding of the luminescence mechanism of Cs2SnCl6:Bi and supplies significant references for developing more perovskite materials with outstanding luminescence.