Photostable Cs0.5Rb0.5PbBr3 Quantum Dots for Whispering Gallery Mode Lasing

TiO2 microspheres encapsulated with photostable Cs0.5Rb0.5PbBr3 quantum dots (QDs) are shown to exhibit whispering gallery mode (WGM) microcavity lasing. Cs0.5Rb0.5PbBr3-QDs have high photostability and photoluminescence quantum yield (PLQY) compared to CsPbBr3- and CsPbI3-QDs. A strong synergy between the TiO2 optical microcavity and the PL emission from Cs0.5Rb0.5PbBr3-QDs serving as the gain medium is evidenced from the WGM-less spontaneous emission arising at a low excitation laser power transitioning to the stimulated lasing emission characteristics of WGM modes beyond the critical threshold of 7.98 kW/cm2. Upon excitation with an Ar-ion laser (lambda ex = 488 nm), a substantial amplification exceeding an order of magnitude is observed at this threshold. The WGM lasing in this system exhibits a high quality factor (Q) of similar to 1807 at room temperature. Remarkably, the Cs0.5Rb0.5PbBr3-QDs remains photostable, with no discernible photodegradation even under an elevated continuous laser power of similar to 20.03 kW/cm2 for 90 min. WGM lasing is also observed in coupled doublet and triplet microspheres; however, the Q-factor decreases as the number of coupled microcavities increases. Rb-substituted halide QDs show potential for photostable, tunable WGM microlaser applications.