Colloidal synthesis and optical properties of Cs2ZnBr4 and Cs3ZnBr5 nanocrystals

A framework to understand the effects of an oxide-ligand environment on the photoluminescence (PL) of rare-earth-element-doped oxynitride compounds is well established, whereas the effects of halide coordination on crystal field splitting and the associated PL emission are rarely studied. In this paper, we report a synthetic route to alkali metal halide NCs of Cs2ZnBr4 and Cs3ZnBr5 with a broad blue PL emission and large Stokes shift. In particular, the zero-dimensional Cs3ZnBr5 phase, in which the isolated [ZnBr]42− units were completely separated by surrounding Cs+ cations, exhibited a strong blue PL emission at 437 nm with a PL quantum yield of 8.92 %. The formation of additional trap states or defects in the Cs3ZnBr5 crystalline lattice can be associated with a relatively considerable bands at 345 and 400 nm of the optical band edge, resulting in singlet-to-singlet transition of localized excitons with a short lifetime of 3.74 ns. Therefore, herein we demonstrate that tunable alkali metal halide NCs have considerable potential for optoelectronic applications.