Samarium doped zinc-phosphate glasses having composition Sm 2 O 3 (x) ZnO (60Àx) P 2 O 5 (40) (where x ¼ 0.1-0.5 mol%) were prepared by melt quenching method. The density of these glasses was measured by Archimedes method; the corresponding molar volumes have also been calculated. The values of density range from 3.34 to 3.87 gm/cm 3 and those of molar volume range from 27.62 to 31.80 cm À3. The optical absorbance studies were carried out on these glasses to measure their energy band gaps. The absorption spectra of these glasses were recorded in UV-visible region. No sharp edges were found in the optical spectra, which verifies the amorphous nature of these glasses. The optical band gap energies for these glasses were found to be in the range of 2.89-4.20 eV. The refractive index and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. The values of refractive index range from 2.13 to 2.42 and those of polarizability of oxide ion range from 6.51 Â 10 À24 to 7.80 Â 10 À24 cm 3 .