Ultrahigh Quality Upconverted Single‐Mode Lasing in Cesium Lead Bromide Spherical Microcavity

Abstract The realization of ultrahigh quality upconverted single‐mode lasing in wavelength‐scale cavity is still a great challenge, because of limitation of microcavity quality, gain medium, and low spontaneous emission coupling efficiency β. In this work, it is demonstrated that inorganic cesium lead bromide (CsPbBr₃) perovskite spheres with size of ≈780 nm serve as a gain medium and whispering‐gallery cavity simultaneously for two‐photon excited single‐mode laser. Lasing mode with a very narrow linewidth (≈0.037 nm) is realized, corresponding to an ultrahigh Q factor ≈1.5 × 10⁴. Surprisingly, the lasing performance of such small microcavity is best among reported naturally formed semiconductor microcavities. Furthermore, room‐temperature single‐mode lasing at same wavelength can be obtained at any angle between −30° and 30°, showing the nearly uniform emission output of the spherical microcavity. This work paves a simple and straight way to obtain ultrahigh Q two‐photon excited single‐mode lasing in micro/nanostructures, holding great promise for practical applications in frequency upconversion, high sensitive sensing in nano‐optics.