Unraveling the triplet excited-state dynamics of Bi^(3+)in vacancyordered double perovskite Cs_(2)SnCl_(6) nanocrystals

Luminescent metal halides doped with ns^(2-)metal ions such as 6s^(2-)metal Bi^(3+)have aroused reviving interest owing to their outstanding optical properties;however,the origin of the photoluminescence(PL)remains controversial and unclear.Herein,we report a strategy for the controlled synthesis of Bi^(3+)-doped vacancy-ordered double perovskite Cs_(2)SnCl_(6)nanocrystals(NCs)and unravel the triplet excited-state dynamics of Bi^(3+)through temperature-dependent PL and ultrafast femtosecond transient absorption spectroscopies.Owing to the aliovalent Bi^(3+)doping in the spatially confined zero-dimensional(0D)structure of Cs2SnCl6,Bi^(3+)ions experience an enhancive Jahn-Teller distortion in the excited state,which results in intense broadband blue PL originating from the inter-configurational 3P0,1→1S0 transitions of Bi^(3+)at 450 nm,with a large Stokes shift and a quantum yield of 35.2%.Specifically,an unusual thermal-enhanced Jahn-Teller splitting of the excitation band and a remarkable transition of the PL lifetime from ms at 10 K toμs at 300 K were observed,as solid evidence for the isolated Bi^(3+)emission.These findings clarify the controversy about the PL origin in ns^(2-)metal ion-doped lead-free luminescent metal halides,thereby paving the way for exploring their optoelectronic applications.