Analysis of the Local Structure around Eu and Mn Ions in Alkaline-Earth Silicate Phosphors for White Light Illumination

M2SiO4-based phosphors (M: alkaline-earth metal) that emit red to blue light are expected to offer high color rendering to white light-emitting diodes (LEDs) in combination with blue or near-UV excitation sources. It is very important for the complete control of the emission color to understand the crystal field around the active elements (rareearth and transition metals). XAFS spectroscopy is applied to a (Ba,Ca)2SiO4:Eu,Mn phosphor at Eu L3and Ba, Ca, Eu, Mn K-edges to elucidate the local environments of Eu and Mn. Eu L3and Mn K-edge XANES spectra showed that Eu and Mn are both divalent, like Ba and Ca. K-edge EXAFS spectra indicated that the local structures of Eu and Mn are similar to those of Ba and Ca, respectively. However, the curve-fitting analysis showed that the first coordination shell of Eu has two Eu–O bonds that are both shorter than the Ba–O bond. FEFF calculations were also performed based on a BaCaSiO4 model constructed from the crystal structure of KNaSO4. They suggested that Eu substitutes both of Ba and Ca sites with some structural modification while Mn is clearly at the octahedral Ca site that is the smallest of the substitution sites.