Geometrical and Electronic Structures of Red Phosphors Doped with 3d Transition Metals

Phosphors have become increasingly important in our lives with the spread of white LEDs in recent years. The most basic structure of a white LED is a combination of a blue LED and a yellow phosphor, but this combination results in a white color with a high color temperature that leans toward bluish-white. Therefore, red and green phosphors are demanding in order to adjust the color temperature and improve color rendering property. In addition to the demands of high efficiency and long-term stability for such phosphors, it is also important that the raw materials are low-priced. Many red phosphors achieve red fluorescence by adding a few percent or less concentration of rare earth elements. However, their supply may become unstable, since rare earth elements are unevenly distributed in certain regions of the earth. Therefore, it is requested that the phosphors without rare-earth elements. Recently we have reported stable rare-earth free res phosphors using 3d transition metals with 3d3 configuration, such as Cr3+ and Mn4+, to replace rare-earth elements [1-3]. In the current study, geometrical and electronic structures of phosphor materials doped with Cr3+ and Mn4+ are demonstrated both experimentally and theoretically. Especially, we focus upon the local environment of doped 3d transition element, which are studied in detail by X-ray absorption near edge structure (XANES) and electron spin resonance (ESR) analysis with the aid of the first-principles calculations. References [1] M.S. Kurboniyon et al., Phys. Status Solidi B260 (2023) 2200575. [2] U. Zafari et al., Opt. Mater.: X 16 (2022) 100197. [3] M. Sagayama et al., ECS J. Solid State Sci. Tech. 10 (2021) 076004.