Blue Na2O - CoO - P2O5 glasses: Structural, physico-chemical, thermal and optical characterizations

Two blue phosphate glasses series, (50-x/2)Na2O - xCoO - (50-x/2)P2O5 (0 ≤ x ≤ 35) and (50-x)Na2O - xCoO - 50P2O5 (0 ≤ x ≤ 50) labelled NaCoPO(I) and NaCoPO(II), were synthesized by the melt quenching route and characterized by diverse techniques. Introduction of cobalt oxide CoO in vitreous NaPO3 metaphosphate induces an increase in the glass transition temperature, a decrease in the molar volume and the dissolution rate of the glasses in distilled water, and therefore a strengthening of the glass network. Raman spectra of NaCoPO(I) series, where O/P ratio varies from 3 to 3.54, show that Co2+ ions breakdown the infinite metaphosphate chains and provoke remarkable structural modifications. In contrast, no significant change was observed in the glassy network of NaCoPO(II) series, where O/P ratio is constant and equal to 3. Optical study results show that Co2+ ions have both octahedral and tetrahedral environments with predominance of tetrahedral coordination. The reduction in band gap energy when CoO content rises is due to the increase of non-bridging oxygen number in the vitreous network. The values of CIE L∗a∗b∗ parameters are consistent with the blue color, sought for commercial pigments. The physical parameters deduced from optical spectra suggest that the studied glasses are promising materials for several applications such as pigments and nonlinear optical materials. Raman and optical study of glasses belonging to the Na2O–CoO–P2O5 ternary system. [Display omitted] •Blue cobalt phosphate glasses (50-x/2)Na2O - xCoO - (50-x/2)P2O5 and (50-x)Na2O - xCoO - 50P2O5 were prepared by melt-quenching method.•Structural approach of these glasses was studied by Raman, FTIR and UV–Visible.•Introduction of Co2+ ions in vitreous NaPO3 breakdowns the infinite metaphosphate chains and strengths the network in (50-x/2)Na2O - xCoO - (50-x/2)P2O5 glass series.•UV–visible study shows that Co2+ ions are in both four and six coordinations.