Quantum confinement luminescence of trigonal cesium lead bromide quantum dots

Cesium lead halides are novel and superior optoelectronic materials. Unlike the cases of the widely investigated cubic CsPbXr(3) (X = Cl, Br, or I) nanocrystals, people know little about the optical properties of the zero-dimensional perovskite Cs4PbX6 nanocrystals. We study the photoluminescence properties of the Cs4PbBr6 quantum dots (QDs) with sizes of only a few nanometers. They exhibit stable wavelength-tunable (from 340 to 378 nm) luminescence stemming from quasi-self-trapped excitons. The spectral characterizations in conjunction with first-principles calculations reveal there is remarkable quantum confinement effect in the Cs4PbBr6 QDs. The large exciton binding energy obtained from both calculation and experiment explains why the trigonal Cs4PbX6 QDs have strong exciton-related absorption and emission at room temperature. This family of wide-gap trigonal cesium lead halide QDs with intrinsic near-UV luminescence have potential applications in short-wavelength photonic nanodevices.