Precise Defect Engineering of Tin and Chlorine Vacancies for Tunable Photoluminescence in Cs ₂ SnCl ₆ Perovskite Variants

Defect engineering provides a promising strategy for modulating the optoelectronic properties of metal halides for versatile photonic applications. However, precise control over defects in metal halides to achieve tunable photoluminescence remains a grand challenge. Herein, a simple yet precise defect engineering strategy based on synthesis‐defect‐luminescence modulation was proposed to develop Cs 2 SnCl 6 and Cs 2 SnCl 6 :Ln 3+ (Ln = Tb 3+ , Eu 3+ ) perovskite variants as tunable emitters via a combined computational‐experimental approach. By controlling the ratio of tin vacancies (V Sn ) and chlorine vacancies (V Cl ), intrinsic Cs 2 SnCl 6 features a tunable emission color from blue to near‐white and to yellow, along with a record‐high yellow emission (photoluminescence quantum yield, PLQY: 28.76%) and anti‐thermal quenching performance, which overcomes the limitation of inefficient and monochromatic emission in traditional Cs 2 SnCl 6 . Moreover, by facilitating more V Cl defects, Cs 2 SnCl 6 :Ln 3+ with stable Ln 3+ doping and remarkably enhanced Ln 3+ emission have been realized through charge‐compensation effects. Furthermore, tunable emission from green to red could be realized via energy transfer (ET) from Tb 3+ to Eu 3+ . Finally, we explored potential applications in solid‐state lighting and information anti‐counterfeiting. Our study not only reveals the intrinsic relationship between defect formation and optical properties in metal halides, but also establishes a rational defect engineering pathway for tuning photophysical properties.