Role of Trap States in Excitation Wavelength-Dependent Photoluminescence of Strongly Quantum-Confined All-Inorganic CsPbBr3 Perovskites with Varying Dimensionalities

All-inorganic CsPbBr3 perovskites have emerged as promising luminescent materials for light-emitting devices owing to their unprecedented photoluminescence (PL) properties. The fundamental understanding of their photophysical properties offers new opportunities to develop high-performance devices. However, the investigation of optical properties of strongly quantum-confined CsPbBr3 perovskites of different morphologies is lacking. Herein, we report the PL properties of strongly quantum-confined CsPbBr3 perovskites with varying dimensionalities, specifically zero-dimensional quantum dots (0D-QDs), one-dimensional quantum wires (1D-QWs), and two-dimensional quantum platelets (2D-QPLs). Results reveal that the PL efficiency displays an overall increase for 0D-QDs and 1D-QWs but a negligible change for 2D-QPLs against the excitation wavelength, all with the observation of multiple local minima. A combined analysis of the excitation wavelength dependence of the PL efficiency, dimensionality dependence of excitonic transition, and time-resolved PL decays implies the presence of two different types of trap states—a continuum of electron trap states and discrete localized trap states. We conclude that both trap states are equally important in both 0D-QDs and 1D-QWs, while discrete localized trap states are dominant in 2D-QPLs. In all these quantum structures, the two trap states do not affect the intrinsic exciton relaxation but could interact with energetically excited electrons beyond the conduction band minimum, thereby decreasing the PL efficiency. Our study presents a fundamental understanding of the PL properties of quantum-confined CsPbBr3 perovskites and may guide the development of the corresponding light-emitting devices.