Temperature-Dependent Photoluminescence of Cesium Lead Halide Perovskite Quantum Dots: Splitting of the Photoluminescence Peaks of CsPbBr3 and CsPb(Br/I)3 Quantum Dots at Low Temperature

We investigated the temperature-dependent photoluminescence (PL) properties of colloidal CsPbX3 (X = Br, I, and mixed Br/I) quantum dot (QD) samples in the 30–290 K temperature range. Temperature-dependent PL experiments reveal thermal quenching of PL, blue shifting of optical band gaps, and line width broadening for all CsPbX3 QD samples with increasing temperature. Interestingly, side-peak emissions that are spectrally separated from the excitonic PL peaks were observed for both CsPbBr3 and CsPb(Br/I)3 QD samples at temperatures below ∼250 K. The side-peak emission for the CsPbBr3 QD sample is located at a lower energy compared to the band-edge peak, whereas that of the Br-rich CsPb(Br/I)3 alloy QD sample is located at a higher energy than that of the band-edge peak. We found that the CsPbBr3 QDs have two emissive states, a band-edge state, and one involving shallow defects, which can be spectrally separated by narrowing the emission line widths at low temperature. In the case of the Br-rich CsPb(Br/I)3 QD sample, the partial halide-segregation-induced heterogeneity of the alloy phase within the ensemble at low temperature leads to blue-shifted radiative recombination channels.