The R and Y/B values due to 5D0–7F2/5D0–7F1 and 4F9/2–6H15/2/4F9/2–6H13/2 luminescence intensity ratios of Eu3+ and Dy3+ ions, respectively, increase with increasing heavy metal (PbO) content, suggesting higher asymmetry and more covalent bonding character between rare earth and oxygen ions.