Highly efficient blue luminescence from stable lead-free Cu-doped Rb₂LiBiBr₆ double perovskites

Highly efficient three-dimensional (3D) lead-free halide perovskites that produce blue light emission with outstanding stability have attracted global research attention. In order to increase the light emission efficiency of Rb₂LiBiBr₆ perovskites, band structure engineering can be performed by doping Cu²⁺ ions. In this work, the structural, chemical and optical characteristics of pure Rb₂LiBiBr₆ (RLBB) and Cu²⁺-doped Rb₂LiBiBr₆ (RLBBC) phosphors produced through conventional wet chemical processes are reported. A narrow and comparatively unique blue emission was exhibited by Cu²⁺-doped Rb₂LiBiBr₆ double perovskites (DPs) as a result of electron-phonon interactions. The phase purity and microstructure of the Rb₂LiBiBr₆:Cu²⁺ DP were assessed using X-ray diffraction and scanning electron microscopy, respectively. All the synthesized samples showed a orthorhombic crystal structure, and B sites had a substantial impact on the Pnma space group in the Rb₂LiBiBr₆ DP framework. The Bi³⁺ ions at the B′ sites were replaced by the doped Cu²⁺ ions, which distributed themselves to an equilibrium valence state and showed minimal variation in the ionic radius. Photoluminescence (PL) spectra were used to explore the corresponding mechanism of the Cu²⁺ → Bi³⁺ energy-transfer process. The Cu²⁺-doped Rb₂LiBiBr₆ (RLBBC) phosphors exhibited a blue emission at 469 nm when excited at 367 nm. It showed an optical bandgap of 2.87 eV at room temperature. This as-prepared perovskite showed outstanding stable chromaticity with (x,y) coordinate values of (0.1367, 0.0596) under a continuous irradiation of 367 nm UV light. This lead-free and highly effective Cu²⁺-Rb₂LiBiBr₆ DP has a wide range of applications in the rarest blue photonic and optoelectronic domains as it demonstrates the potential to overcome the obstacles of extreme toxicity and inadequate stability.