Efficient Broadband Yellow-Green Emission of Vacancy Halide Double Perovskites Through the Ion-Exchanged Strategy

Broadband high-efficiency luminescent materials have become a hot spot in lead-free perovskite research. There are relatively few broadband yellow-green phosphors with both ultraviolet and blue excitation ranges, which make them more suitable for phosphor-converted white LEDs. Through the ion-exchanged strategy, Cs₂Hf_1-TeCl₆ (CH_1-TC) vacancy halide double perovskites were successfully prepared at room temperature. Using different excitation ranges of CH_1-TC, two types of high-quality white LEDs are obtained. By combining density functional theory calculations and experiments, it is proved that this bright broadband yellow-green emission (photoluminescence quantum yield of 83.46%) is not only derived from the ion transitions of Te⁴⁺ but also exhibits the inherent characteristics of self-trapped exciton emission. Our results not only broaden the application fields of lead-free halide perovskites but also provide further insights into the luminescence mechanism.