Ultralow Threshold Lasing from a Continuous-Wave-Pumped SiNx/CsPbBr3/Ag Thin Film Mediated by the Whispering Gallery Modes of a SiO2 Microsphere

Thin-film pervoskite lasers driven by a continuous wave (CW) laser with ultralow thresholds, which is crucial for the development of on-chip electrically driven lasers, have not yet been realized owing to the low excitation power density of the CW laser. Here, we reported the CW-laser-pumped lasing from a thin film of CsPbBr₃ quantum dots (QDs) sandwiched by a SiN_x and a Ag thin film and mediated by the whispering gallery modes of a SiO₂ microsphere. The stable photoluminescence from CsPbBr₃ QDs with a quantum efficiency of ∼45% is realized by encapsulating with a thin SiN_x film. Upon CW-laser pumping, lasing from the whispering gallery modes with a threshold of ∼11.6 W/cm² is successfully demonstrated at room temperature. The strong localization of electric field achieved in the particle-on-film system, which is revealed in the numerical simulations and lifetime measurements, plays a crucial role in the realization of the ultralow threshold lasing. Our findings open a new avenue for designing photostable CW-laser-pumped pervoskite lasers.