Lithium based zinc-phosphate containing Sm2O3 glasses of the system (5-x) Li2SO4 − 20Li2O − 45P2O5 − 30ZnO - xSm2O3, (where x = 0, 0.1, 0.5, 1, 2 and 3 mol%) were prepared by melt quenching technique. The amorphous nature of the prepared glasses is ascertained by X-ray diffraction. The density and molar volume are found to vary non-linearly with Sm2O3 content. The addition of modifier oxides such as Li2O to P2O5 glass would break P-O-P bonds and resulting in the creation of non-bridging oxygen’s. The creation of non-bridging oxygen atoms makes the structure less rigid and would leads to the formation of weaker phosphate structural entities. This would lead to the formation of voids between the phosphate groups. The addition of alkali and samarium content in the phosphate glasses is accountable for the collective number of the non– bonded oxygens and this may cause a non-linear variation in the volume of the network structure which in turn lead to non-linear variation in the density. The optical spectrum consists of a characteristic Ultraviolet absorption bands of Sm3+ ions in the range 200–400 nm and other strong bands at 940 nm and 1100 nm which are considered to originate from the transitions of ground state to the different excited states. The optical band gap energies were determined from both ultraviolet band edges and Tauc’s plots. The band gap energy varies non-linearly with Sm2O3 content. The non-linear variation in density, molar volume and band gap energy discloses the intermediate-range structure composed of PO4and ZnO4tetrahedra and are discussed in view of the polymeric chain of phosphate network structure.