Room-temperature synthesis of CsPbBr3@CsPb2Br5 microcrystals and their upconversion luminescence

In this work, a convenient and environmental-friendly aqueous-phase method is used to synthesize CsPbBr3@CsPb2Br5 microcrystals (MCs) at room temperature, of which structural and optical properties are characterized by powder X-ray diffraction (PXRD), absorption, and photoluminescence (PL) spectroscopic techniques. Two obvious absorption peaks at 307 and 515 nm are attributed to CsPb2Br5 matrix and CsPbBr3 impurity, respectively. Full-width at half-maximum (FWHM) of PL for MCs is 83.5 meV at room temperature, and its emission peak is observed at 518 nm. With the temperature changed from 80 to 340 K, the fitted value of the exciton binding energy is 84.1 meV from temperature-dependent steady-state PL. Upconversion luminescence (UCL) can be observed obviously under near-infrared femtosecond laser pulse excitation, which is compared with normal luminescence from steady-state and time-resolved PL measurements. The experimental investigations show that CsPbBr3@CsPb2Br5 MCs have excellent stability against thermal, water and light irradiation, which will provide a new choice for the commercial applications to lasering and displaying.