Efficient White Photoluminescence from Self-Trapped Excitons in Sb³⁺/Bi³⁺-Codoped Cs₂NaInCl₆ Double Perovskites with Tunable Dual-Emission

Efficient and stable inorganic lead-free halide perovskites have attracted tremendous attention for next-generation solid-state lighting. However, single perovskite phosphors with strong, tunable-color-temperature white-light emission are rare. Here, a doping strategy was developed to incorporate Sb3+ and Bi3+ ions into Cs2NaInCl6 single crystals. Blue and yellow emission for white light with a 77% quantum yield was observed. The dual-emission originates from different [SbCl6]3– octahedron-related self-trapped excitons (STEs). The blue emission is attributable to limited Jahn–Teller deformation from Sb3+ doping. Large-radii Bi3+ increase the deformation level of the [SbCl6]3– octahedron, enhancing yellow STE emission. Density functional theory calculations indicated that the Bi3+ doping forms a sub-band level, which produces yellow STE emission. Tuning between warm and cold white light can be realized by changing the Sb3+/Bi3+ doping ratio, which suggests a unique interaction mechanism between Sb3+ and Bi3+ dopants, as well as Bi3+-induced lattice distortion in double perovskites.