Red‐Emitting Perovskite Variant Cs₂PtCl₆ Phosphor: Material Design, Luminous Mechanism, and Application in High‐Color‐Rendering White Light‐Emitting Diodes

Abstract Recently, A₂BX₆‐type halide perovskite variant phosphors have been applied for white light‐emitting diodes (LEDs) due to their superior photoluminescence properties, excellent stability, and low‐cost solution‐processability. However, the reported white LEDs, particularly the all‐A₂BX₆ white LEDs, exhibit insufficient color rendering due to the shortage of red light. In this work, through a rational material design, a red‐emitting perovskite variant Cs₂PtCl₆ phosphor is developed. The synthesized Cs₂PtCl₆ powders exhibit a relatively narrow bandgap of 2.91 eV and an intrinsic broadband red emission centered at 670 nm, which is attributed to the triplet self‐trapped excitons associated with the Jahn−Teller‐distorted [PtCl₆]²⁻ octahedra in the excited state. Using Cs₂PtCl₆ as the red phosphor component, an all‐A₂BX₆ white LED is constructed, achieving a standard white light with a Commission Internationale de l'Eclairage chromaticity coordinate of (0.33, 0.33), a correlated color temperature of 5318 K, and a record high color rendering index of 90. This work represents a significant step toward the application of A₂BX₆ perovskite variant phosphors for solid‐state lighting.