Multiband lasers are attractive for their potential applications in color display, lighting, wavelength-division multiplexing, optical communications, and computing.1–4 Rare earth (RE) elements with abundant long-lived intermediate energy levels and intraconfigurational transitions can emit light from the deep-ultraviolet to mid-infrared by pumping high-energy or low-energy photons, i.e., downshifting or upconversion, respectively, and thus can be applied in data storage,5,6 three-dimensional display,7,8 luminescent biomarkers,9–11 and lasers.12,13 Whispering-gallery-mode (WGM) optical microcavities with an ultrahigh quality () factor and small mode volume exhibiting ultrahigh energy density and strong light–matter interaction can be applied in sensing,14–16 nonlinear optics,17–22 cavity optomechanics,23,24 and lasers.25–33 Therefore, doping RE elements into an ultrahigh- microcavity without degrading its intrinsic factor is an effective way to construct a low-threshold and narrow-linewidth multiband microlaser.