Strongly luminescent and highly stable CsPbBr3/Cs4PbBr6 core/shell nanocrystals and their ultrafast carrier dynamics

All-inorganic lead halide perovskites nanocrystals (NCs) have been demonstrated to be promising candidates for optoelectronic devices, but preparing perovskite NCs with high photoluminescence quantum yields (PLQYs) and excellent stability has been a challenge. In this work, CsPbBr3/Cs4PbBr6 core/shell NCs with a PLQYs of 87.23% and long-term stability in ambient environments was prepared by room temperature inverse microemulsion method. The excellent stability of the sample was attributed to the protection of Cs4PbBr6, and higher PLQYs could be owing to the passivation effect of the core/shell structure. To illustrate the distribution of photogenerated carrier in the core/shell structure, a confined excitons model was proposed based on time-resolved PL and temperature dependent PL measurements. Femtosecond time-resolved transient absorption spectra measurements were performed upon different excitation wavelength to unveil the photogenerated carrier dynamics in core/shell NCs. Upon 300 nm excitation, a carrier transfer process with the time of 3.18 ps from shell to core layer was observed. Furthermore, both two- and three-photon absorption PL was discovered in core/shell NCs, further verifying the carrier transfer process.