Highly efficient Sb3+ emitters in 0D cesium indium chloride nanocrystals with switchable photoluminescence through water-triggered structural transformation

All-inorganic lead-free luminescent metal halide nanocrystals (NCs) have shown great promise in optoelectronics but their applications are limited by the low photoluminescence (PL) efficiency. Herein, we report a strategy via Sb3+ alloying to achieve highly emissive 0D In-based halide NCs and investigate the effect of NC size on the optical properties and excited-state dynamics of Sb3+. Owing to the strong electron-phonon coupling of Sb3+ in the spatially confined 0D structure of Cs3InCl6, Sb3+ ions experience a dynamic Jahn-Teller distortion in the 3P1 excited state and an off-center position in the 1S0 ground state, which results in intense broadband emission of Sb3+ from the inter-configurational 3P1 → 1S0 transition with a large Stokes shift and a high PL quantum yield (QY) of 52.3%. Furthermore, through an interfacial reaction with water, the green-emitting Cs3InCl6: Sb3+ NCs can be transformed into the orange-emitting Cs2InCl5·H2O: Sb3+ NCs with a PLQY up to 75.3%. These findings reveal the unique advantage of the 5s2-metal Sb3+ luminescence in 0D metal halide NCs, thereby opening up a new avenue for exploring novel and versatile lead-free luminescent metal halide NCs through ns2-metal ion doping or alloying.