Abstract A series of europium doped Na₂O-B₂O₃-SiO₂, PbO-GeO₂ and ZnOTeO₂ glasses was investi-gated by means of¹⁵¹ Mössbauer spectroscopy. The distortion of the Eu sites has been evaluated in the Na₂O-B₂O₃-SiO₂ glasses by means of the quadrupolar interaction parameter and the asym-metry parameter; the disorder has been estimated by the line width. The occupancy of the sites in the borosilicate glasses is discussed. The correlation of the isomer shift with the optical basicity of the glass is discussed in terms of the degree of covalence of the Eu-O bond.