Chemical Group Substitution Enables Highly Efficient Mn4+ Luminescence in Heterovalent Systems

Hong Ming, Yifei Zhao, Yayun Zhou, Maxim S. Molokeev, Yuanjing Wang, Enhai Song, Qinyuan Zhang// Advanced Optical Materials//

Defects are a double-edged sword for heterovalent metal-ion doping phosphors. Along with the luminescence tunability of phosphors bestowed by defects, their expected luminescence efficiency would also be inevitably lowered due to the presence of these quenching sites. Herein, a chemical group substitution strategy is proposed, where inorganic polyhedrons act as the smallest chemical units during the structural evolution of the doping process. Such a method can not only effectively prevent the defect generation for charge compensation in heterovalent doping systems, but also facilitate the incorporation of activators into the matrix, leading to extremely high luminescence efficiency. The concept is first confirmed energetically favorable by first-principles simulations. As a robust experimental proof, two newly reported Mn4+-incorporated hexavalent organic-inorganic hybrid oxyfluorides (TMA)2BO2F4:Mn4+ (where TMA stands for tetramethylammonium, and B = W6+ or Mo6+) present high quantum efficiency (up to 94.4%) and short lifetime (down to 2.26 ms) that are superior to the commercial red phosphor K2SiF6:Mn4+ (≈84.8%, ≈8.06 ms). Utilizing the differences in decay lifetimes and thermal quenching behaviors of (TMA)2BO2F4:Mn4+ and K2SiF6:Mn4+, a time- and temperature-resolved single-color multiplexing mode with high-safety and easy-access is developed for information security. This work offers an effective strategy to manipulate defect generation in luminescent materials.