Experimental and Theoretical Analysis of Photoluminescence from Mn-Doped Oxide Phosphors

Abstract

Most of the current phosphor materials are prepared by doping dilute amount of rare-earth or transition metal ions, which act as emission center, in matrix materials. Among such phosphors, rare-earth doped oxides show good properties such as high luminescence and high stability for long term use, etc. However, due to the limitation of the rare-earth elements in the earth, rare-earth free phosphor materials have been strongly demanding, and therefore such materials have been extensively investigated these years. Although there are wide varieties of dopants for such rare-earth free phosphors, Mn4+ doped phosphor materials, which show red emission, are one of the most attractive materials. In order to design new phosphors doped with Mn ions, it is essential to know the local environment of the doped Mn ions in an atomic scale and the electronic structures of Mn-doped materials. Although the local environment analysis is mandatory, such analysis is very difficult for dilute dopants. In the current study, local environment analysis of Mn ions doped in some oxides were carried out by using the X-ray absorption near edge structure (XANES) measurements and the electronic structure calculations for such materials have been performed with the first principles calculations.All the samples were fabricated with the conventional solid-state reaction method changing the concentration of Mn ions and/or matrix oxides, such as CaTiO3, CaZrO3, CaSnO3, CaAl12O19, Mg2TiO4 and so on. Crystal structures of the synthesized materials were characterized with powder X-ray diffraction technique. Mn K- and L- XANES spectra were observed at BL9C of KEK-PF in the transmission mode and BL4B in UVSOR in total electron yield mode, respectively. Theoretical XANES spectra to be compared with the experimental ones were prepared with the WIEN2k package [1]. Prior to the detailed electronic structure calculations, geometry optimizations were carried out computationally to investigate the local environment of the doped Mn ions in the matrix oxides by the first principles calculations within a density functional theory level using the Vienna Ab-initio Simulation Package, VASP [2]. The electronic structures of the Mn-doped materials after above geometry optimizations were investigated with modified Becke-Johnson potential [3], which was recently developed electron-electron correlation functional and implemented in WIEN2k package is accurate for the band-gap estimation of the wide variety of semiconductors.AcknowledgementThis work was partially supported by the Joint Research Center for Environmentally Conscious Technologies in Materials Science (project No. 30009, 30012, 31008, and 31017) at ZAIKEN, Waseda University.