Fig. 1. Phase-change perovskite vertical microcavity laser. (a) Schematic of a tunable microlaser based on phase-change perovskite gain medium, sandwiched between Au mirror and DBR reflector sitting on a quartz glass substrate, pumped by blue-violet laser (λ = 405 nm) and emitting a tunable beam in the near-IR from 790.7 nm to 799.5 nm. (b) Conceptual depiction of the two crystal structures of MAPbI₃, the low-temperature (130 K) orthorhombic state and room-temperature (298 K) tetragonal state. (c) Cross-sectional SEM picture of the VCSEL. The inset shows a zoomed-in image to present the optimized morphology of Ta₂O₅/ SiO₂ films. Scale bar: 1 μm. (d) The SEM image of a ~300 nm-thick MAPbI₃ film residing on the DBR reflectors. Scale bar: 500 nm. The inset is a photograph of the vertical microcavity, scale bar: 1 cm.

Fig. 2. (a) The absorptance and PL spectra of MAPbI₃ nanocrystalline film with tetragonal (130 K, orange line) and orthorhombic (160 K, green line) states, respectively. (b) The ASE spectra of MAPbI₃ phase change perovskite with the structural states of tetragonal (130 K, orange line) and orthorhombic (160 K, green line), respectively. (c) Reflectance spectra of top Au flake (orange line) and bottom DBR (green line), the green dashed line is the simulation of the bottom DBR reflectance spectra. (d) The measured PL spectra of the MAPbI₃ based microcavity with the different states of tetragonal (29.5 μJ cm⁻²) and orthorhombic (8.1 μJ cm⁻²).

Fig. 3. Laser performance of the VCSEL microlaser at different perovskite phase states. (a) Performance of the VCSEL microlasers based on the tetragonal MAPbI₃: 130 K radiation spectra of the VCSEL against pump fluence (left column); light-light curve of the tetragonal laser at 130 K (right column). (b) Performance of the VCSEL with the orthorhombic MAPbI₃: room-temperature radiation spectra of the VCSEL against pump fluence (left column); light-light curve of the orthorhombic laser at 160 K (right column).

Fig. 4. (a) The L−L curve for the MAPbI₃ VCSEL by increasing the temperature from 130 K to 160 K. (b) Lasing threshold pumping fluence versus temperature for the device. Stability characterizations of the VCSEL under fs pulsed excitation with pumping fluence at 1.1 F_th for both (c) tetragonal and (d) orthorhombic states, respectively.