Luminescence Enhancement of K2LiAlF6:Mn4+ Phosphors by Zn2+-Mediated Charge Compensation for Fast-Response Backlighting Applications

Wide-spectrum displays require narrow-band red phosphors activated by Mn⁴⁺, but most of them, such as K₂SiF₆:Mn⁴⁺, have long fluorescence decay lifetimes (>7 ms) that hinder their use in fast-response backlights. Interestingly, K₂LiAlF₆:0.05Mn⁴⁺ has a shorter fluorescence lifetime (3.43 ms), but its disadvantage is that its luminescence intensity is relatively weak. So, in this study, the luminescence intensity of K₂LiAlF₆:0.05Mn⁴⁺ is improved by doping with Zn²⁺. The experimental results show that enhancement of the luminous intensity is as high as 39%, the fluorescence lifetime is only increased by 13% (3.89 ms), and it is still less than 4 ms. Through experiments and differential charge density calculations, it has been revealed that the luminescence intensity improvement is due to an increased crystalline quality during the synthesis process. Specifically, the co-doping of Zn²⁺ reduces the formation of impurity ions Mn²⁺ and Mn³⁺ and the generation of K⁺ vacancies caused by nonequivalent doping. We demonstrate the advantage of this phosphor over K₂SiF₆:Mn⁴⁺ in terms of response speed by using a camera. It emits only weak red light after the blue chip stops working for 5 ms, indicating its potential application in next-generation fast-response displays.