Zr Alloying‐Induced Bandgap Tunability and Enhanced NIR Photoluminescence in Vacancy‐Ordered Cs ₂ WCl ₆ Double Perovskites

Broadband near‐infrared (NIR) light‐emitting materials are essential for developing the next generation of intelligent NIR light sources. Emerging halide perovskite materials are considered highly promising candidates in the field of optoelectronics due to their excellent optical properties and suitability for solution‐based fabrication. However, achieving efficient and thermally stable broadband NIR photoluminescence in these materials remains a significant challenge. In this study, a zirconium (Zr) alloying strategy was employed to modify the vacancy‐ordered double perovskite Cs 2 WCl 6 , significantly enhancing its broadband NIR photoluminescence and enabling the tunability of its optical bandgap. A series of Cs 2 W 1‐x Zr x Cl 6 samples (0 ≤ x ≤ 1) were successfully synthesized, with the optical bandgap expanding from 1.17 eV for x = 0 to 3.26 eV for x = 1. The Zr 4+ ‐alloyed material exhibited a 24‐fold increase in NIR photoluminescent quantum yield and an extension of the exciton lifetime from 9.94 to 42.77 µs. Furthermore, density functional theory (DFT) calculations and temperature‐dependent photoluminescence spectra indicate that Zr 4+ alloying optimizes the microstructural environment of the Cs 2 WCl 6 luminescent centers. This process weakens electron‐phonon coupling and breaks parity‐forbidden transitions of [WCl 6 ] 2− . The study demonstrates the effectiveness of metal ion alloying in tuning the bandgap and enhancing NIR photoluminescence in double perovskites.