Efficient and stable emission of warm-white light from lead-free halide double perovskites

Lighting accounts for one-fifth of global electricity consumption¹. Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties^2,3; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn-Teller distortion of the AgCl₆ octahedron in the excited state. By alloying sodium cations into Cs₂AgInCl₆, we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor⁴. This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs₂AgInCl₆. The optimally alloyed Cs₂(Ag_0.60Na_0.40)InCl₆ with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies.