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

Abstract

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 V_Cl 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.