Fig. 1. Characterizations of RbPbBr3 MCCs. (a) Typical SEM images of the RbPbBr3 MCCs. Inset: magnified image of an individual RbPbBr3 MCC. (b) Selected area electron diffraction pattern of an individual RbPbBr3 MCC. Inset: TEM image of a RbPbBr3 MCC. (c) EDX elemental mapping of a RbPbBr3 MCC, displaying its uniform composition. (d) SEM images of several RbPbBr3 microstructures located at different growth positions. (e) Shape evolution process from a microsphere to a microcube. (f) PL spectrum of as-grown RbPbBr3 MCCs excited using a 405 nm continuous wave laser at room temperature. Inset: PL image of an individual RbPbBr3 microcube. (g) Time-resolved PL curves of a RbPbBr3 microcube (red line) and a RbPbBr3 microsphere (blue line).

Fig. 2. Single-mode lasing characteristics of RbPbBr3 MCC lasers. (a) Individual RbPbBr3 MCC pumped by a 400 nm fs-laser (approx. 40 fs, 10 kHz). (b) Resonant optical modes of RbPbBr3 MCCs with different sizes. Single-mode lasing was achieved, and the spacing between two adjacent modes decreased with increasing cavity size. (c) Excitation power-dependent lasing spectra obtained from a single RbPbBr3 MCC. (d) Output intensity (red) and FWHM (blue) as a function of the pump intensity. The integrated lasing intensity as a function of the pumping density obtained from the RbPbBr3 MCC indicates that the lasing threshold Pth is 6.76  μJ/cm2. (e) Lorentz fitting of a lasing oscillation mode at 471.7 nm, yielding an ultrasmall linewidth of ≈2200, corresponding to a high Q-factor of ≈2200. (f) Single-mode lasing spectra of four RbPbBr3 MCCs with different sizes. Inset: relationship between the wavelength of single-mode lasing and the sizes of RbPbBr3 MCCs.

Fig. 3. Polarization properties of RbPbBr3 MCC lasers. (a) Emission spectrum below the lasing threshold (≈0.6Pth) obtained from a single RbPbBr3 MCC under various polarizer rotation angles (θ, in degree). (b) Integrated PL intensity as a function of θ. (c) Emission spectrum above the lasing threshold (≈1.2Pth) obtained from the same RbPbBr3 MCC under various polarizer rotation angles. (d) Integrated lasing peak intensity as a function of θ.

Fig. 4. RbxCs1−xPbBr3 MCCs with wavelength tunable emission and high heat stability. (a) PL spectra of RbxCs1−xPbBr3 MCCs. (b) Temperature-dependent PL spectra of CsPbBr3 and Rb0.75Cs0.25PbBr3 MCCs. (c) Comparison of the fluorescence intensity for CsPbBr3 (blue) and Rb0.75Cs0.25PbBr3 (red) MCCs with increasing temperature. (d) Single-mode lasing spectra of RbxCs1−xPbBr3 MCCs.