Metal-halide perovskites are promising optical gain materials because of their excellent photophysical properties. Recently, large perovskite single crystals with phase purity, less defects, and over millimeter dimensions have been successfully synthesized. However, the optical gain effect from these large-size single crystals has not yet been realized. Herein, we for the first time report efficient two-photon pumped amplified spontaneous emission (ASE) from millimeter-sized CsPbBr 3 single crystals (SCs) with a low threshold of 0.65 mJ cm −2 and an optical gain of 38 cm −1 . Furthermore, the CsPbBr 3 SCs also exhibit ultrastable ASE under continuous laser irradiation for more than 40 h (corresponds to 1.5 × 10 8 laser shots) at ambient condition. This work suggests the potential application of large-size perovskite single crystals in practical nonlinear optical devices.

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In optically pumped laser systems, rare gas lasers (RGLs) are a field of great interest for researchers. Gas laser regimes with metastable Ne, Ar, and Kr atoms have been investigated, while studies of RGLs based on metastable Xe are sparse. In this work, when a strong excitation laser (2.92 mJ/pulse, 7.44 × 10 W/cm) was applied to excite Xe atoms from the ground state to the 6p[1/2] state, an interesting phenomenon emerged: An intense fluorescence of 980 nm (6p[1/2]-6s[3/2]) was produced. However, when the energy of excitation laser was decreased to 0.50 mJ/pulse (1.27 × 10 W/cm), the fluorescence of 980 nm became very weak. Besides, lifetime and decay rate constant of the 6p[1/2] state under the condition of E = 2.92 mJ are significantly different from either those measured by other groups or those of E = 0.50 mJ. These phenomena indicate that the high energy of excitation laser should trigger some new kinetic mechanisms. Further works identified that the new kinetic mechanism is the MIR ASE of 3408 nm (6p[1/2]-6s'[1/2]). The mechanisms are proposed as follows. Substantial 6p[1/2] atoms are produced by laser excitation. Then, the ASE of 3408 nm (6p[1/2]-6s'[1/2]) is quickly produced to populate substantial 6s'[1/2] atoms. The 6s'[1/2] atoms can readily arrive at the 6p[1/2] states through collision by virtue of the small energy difference (84 cm) and high collision rate constant of the transition from the 6s'[1/2] state to the 6p[1/2] state. As a result, the intense fluorescence of 980 nm is generated.