Investigation on Luminescent Properties of Rare Earth Doped Mullite Phosphors and the Occupation Site of the Doped Rare Earths

Abstract

© The Author(s) 2019. Full color phosphors based on a host material of mullite (Al6Si2O13) doped with rare earth (Ce3+, Eu2+, Ce3+-Tb3+, and Eu3+) were investigated for the possible application for high power LED lightings. Doping these rare earth ions separately resulted in blue, green and red emissions. The mullite phosphors kept 70% of the luminescence intensity even at 200°C, which was explained by the low thermal lattice vibration associated with the low thermal expansion coefficient. Based on the ionic radii and the bond valence sums, the rare earth ions were considered to occupy the vacant Oc site surrounded by 8 oxygens with a void of 2.14 Å in diameter. Electron density mapping derived from the Rietveld analysis revealed the excess electron density around the Oc site as the possible occupation site for the rare earth ions.