Eu³⁺-Bi³⁺ Codoping Double Perovskites for Single-Component White-Light-Emitting Diodes

Double perovskites (DPs) with Cs₂AgInCl₆ composition, as one of the lead-free perovskites, have been in the spotlight owing to their intriguing optical properties, namely, self-trapped exciton (STE) emission and dopant-induced photoluminescence. However, the current DPs still face the challenge of low photoluminescence efficiency and cannot be applied in practice. Herein, we synthesize the Bi³⁺ and Eu³⁺ codoped Cs₂AgInCl₆ DPs, which displays enhanced STE and Eu³⁺ ions characteristic emissions. Our results indicate that the Eu³⁺ ions mainly substitute the In sites and can increase the radiative recombination rate and exciton binding energy of STEs, which is discovered that Eu³⁺ ions can promote the localization of STEs by breaking the inversion symmetry of the Cs₂AgInCl₆ lattice. The existence of Bi³⁺ ions decreases the excitation (absorption) energy, provides a new absorption channel, and increases the energy transfer rate to Eu³⁺ ions. Through adjusting the Bi³⁺ and Eu³⁺ concentrations, a maximum photoluminescence quantum yield of 80.1% is obtained in 6% Eu³⁺ and 0.5% Bi³⁺ codoped Cs₂AgInCl₆ DPs. Finally, the high-quality single-component white-light-emitting diodes based on Bi³⁺ and Eu³⁺ codoped Cs₂AgInCl₆ DPs and a 410-nm commercial ultraviolet chip are fabricated with the optimum color rendering index of 89, the optimal luminous efficiency of 88.1 lm/W, and a half-lifetime of 1,493 h. This work puts forward an effective lanthanide and transition metals codoping strategy to design single-component white-light emitter, taking a big step forward for the application lead-free DPs.