Abstract: The zero-dimensional perovskite composite Cs₄ PbBr6 /CsPbBr₃ has attracted significant attention for its remarkable photoluminescence (PL), which remains highly effective even in solid state. This work presents a detailed analysis of the steady-state and time-resolved PL (TRPL) behavior of millimeter-scale Cs₄ PbBr₆ /CsPbBr₃ crystals over a temperature range of 80 to 360 K, which covers exciton binding en-ergy, phonon energy, and PL peak energy shifting with increasing temperature. According to the results, Cs₄ PbBr6 /CsPbBr₃ exhibits high exciton binding energy and phonon energy, with calculated values of 358.7 and 94.8 meV, respectively. Specifically, when the temperature is below ∼235 K, thermal expan-sion dominates to influence the TRPL and peak energy, whereas electron-phonon interaction becomes the dominant factor as temperature rises from 235 to 325 K. It is found that Cs₄ PbBr₆ /CsPbBr₃ has a PL behavior similar to CsPbBr₃, and characterization and TRPL results demonstrate that nanometer-scale CsPbBr₃ crystals embed in the Cs4 PbBr6 bulk matrix. Meanwhile, a white light-emitting diode (WLED) device based on Cs4 PbBr₆ /CsPbBr₃ with luminous efficiency of 64.56 lm/W is fabricated, and its color coordinate is measured as (0.34,0.31) under 20 mA, which is in close proximity to the standard white color coordinate. Moreover, the color gamut of the device is measured as 128.66% of the National Televi-sion Systems Committee (NTSC). The WLED electroluminescence (EL) spectra show high Correlated Color Temperature (CCT) stability for the working current varying from 5 to 100 mA, and after continuous oper-ation for 12 h, the EL intensity decreases and stabilizes at ∼70% of the initial EL intensity. These findings suggest that Cs₄ PbBr₆ /CsPbBr₃ crystals are a promising candidate for WLEDs.

Key words: Zero-dimensional perovskites, Photoluminescence, Exciton binding energy, White light-emitting diode