Role of Octahedron Alloying in Photodynamics of Lead-Free Halide Double Perovskite Nanoplatelets

The lead-free halide double perovskites have attracted great interest owing to their unique photophysical properties. Among them, the luminescence mechanisms of the Cs 2 AgInCl 6 crystallites are still under debate. A hot-injection method is developed to synthesize novel hollow and spatially symmetric Cs 2 AgInCl 6 nanoplatelets (NPLs) and study the effect of the cation/octahedron alloying on their photodynamics by using the experimental characterizations in conjunction with the density functional theory calculations. The results reveal that the pure Cs 2 AgInCl 6 NPLs exhibit wide-band and double-peaked photoluminescence originating separately from free and self-trapped excitons. The Ag + /Na + and In 3+ /Bi 3+ alloying, that is, the partial substitution of the [AgCl 6 ] 5− and [InCl 6 ] 3− octahedra by [NaCl 6 ] 5− and [BiCl 6 ] 3− octahedra, leads to crystal symmetry breaking and strongly enhanced exciton localization. As a result, the self-trapped exciton luminescence becomes predominant in the yielded Cs 2 AgInCl 6 :NaBi nanoplatelets, and the quantum yield is highly improved to 10.8%. These results improve the understanding of the role of octahedron alloying in the photophysics of the double perovskite nanocrystals and pave the way for their applications in solid-state lighting.