The thermal stability and structural site-distribution of Eu3+ ions in the red-emitting phosphors Ca9Eu2W4O24 and Sr9Eu2W4O24

Abstract

The red-emitting phosphors Ca9Eu2W4O24 and Sr9Eu2W4O24 were synthesized by the solid-state reaction method. The crystal phases were characterized by X-ray powder diffraction. The photoluminescence excitation and emission spectra were investigated. The luminescence excitation and emission spectra confirm that the phosphors are efficiently excited by near UV light. The dependence of luminescence intensities on the heating temperatures was investigated. The Ca9Eu2W4O24 phosphor exhibits higher thermal stability than that of Sr9Eu2W4O24. The crystallographic sites for Eu3+ ions in Ca9Eu2W4O24 and Sr9Eu2W4O24 are investigated by the site-selective excitation spectra in the 5D0→7F0 wavelength region. It is identified that the Eu3+ ions occupy only M sites (statistically occupied by 0.5Eu and 0.5Ca) in Ca9Eu2W4O24 and, however, the Eu3+ ions can substitute both M sites (Eu3++Sr2+) and Sr2+ sites in Sr9Eu2W4O24. The luminescence spectra and the thermal stability are discussed on the basis of the crystal structure, Eu3+ site-distributions and the energy transfer.