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

► The photoluminescence spectra of Ca9Eu2W4O24 and Sr9Eu2W4O24 were investigated. ► The site-occupancy of Eu3+ ions were determined by the laser site-selective spectra. ► Eu3+ ions have only one site in Ca9Eu2W4O24 and have two disordered sites in Sr9Eu2W4O24. ► The luminescence thermal stability was discussed on the base of the crystal structure. ► The microstructure of Eu3+ ions has great influence on the luminescence.