Enhancing quantum efficiency of Mn4+-doped fluoride phosphors through reverse doping strategy toward potential biological detection

Mn4+-doped fluoride red-emitting materials are renowned for their distinct characteristics, including fixed emission peaks and narrow spectral emission, rendering them highly favored in photoluminescent light-emitting diodes (LEDs). However, achieving ultra-high-concentration Mn4+ doping in fluoride phosphors is imperative to enhance quantum efficiency. Nevertheless, attaining such doping levels in metastable compound systems poses considerable challenges. In this study, we introduce an innovative reverse doping strategy, leading to the synthesis of Mn4+-doped cubic K2SiF6 phosphor (11.38 mol %) from hexagonal K2MnF6. Remarkably, this approach significantly improves the external quantum efficiency (EQE) to 66.7 % upon 450 nm excitation. Through systematic comparisons with conventional co-precipitation and ion exchange methods, our findings unequivocally demonstrate the superior efficacy of this approach in achieving high-concentration Mn4+ ion doping within relatively insoluble matrices. The successful application of our optimized phosphor enabled the fabrication of a red light-emitting diode (LED) that exhibits an exceptional photoelectric efficiency of 31.67 % at 350 mA, surpassing the performance of a commercial red LED chip. Furthermore, the stable red-light emission from the phosphor-converted LED (pc-LED) proves instrumental in rapid-response vascular imaging, showcasing the potential of our findings in advancing light sources for biological detection applications. This research provides valuable insights into enhancing red emission efficiency in slightly-soluble fluoride phosphors via novel synthetic strategy, unlocking possibilities for the development of highly efficient light sources in biological detection and imaging applications.