The influence of different alkaline earth oxides on the structural and optical properties of undoped, Ce-doped, Sm-doped, and Sm/Ce co-doped lithium alumino-phosphate glasses

- Structural study of 10 Al2O3 - 10 Li2O - 50 P2O5 - 30 MO (M = Mg, Ca, Sr, Ba) glasses by FT-IR and Raman spectroscopy.
- The optical basicity Λ correlates with the oxygen polarizability αO2- and the optical band gap Eg.
- Due to electronic transitions of trace level impurities absorbing in the UV-Vis region, Eg is often underestimated.
- After CeO2 and/or Sm2O3 doping, increased the intensity of Sm3+ f-f transitions with increasing optical basicity of the glass.
- The extend of overlap of Ce3+ and Sm3+ absorptions depends not only on the CeO2 concentration but also on the modifier type.

Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with different alkaline earth modifiers were prepared by melt quenching. The structure of the prepared glasses was investigated by FT-IR and Raman, as well as by optical spectroscopy. The effect of the optical basicity of the host glass matrix on the added active dopants was studied, as was the effect doping had on the phosphate structural units. The optical edge shifts toward higher wavelengths with an increase in the optical basicity due to the increased polarizability of the glass matrix, but also with increasing CeO2 concentration as a result of Ce3+/Ce4+ inter valence charge transfer (IV-CT) absorption. The optical band gap for direct and indirect allowed transitions was calculated for the undoped glasses. The glass sample containing Mg2+ modifier ions is found to have the highest value (4.16 eV) for the optical band gap while Ba2+ has the lowest value (3.61 eV). The change in the optical band gap arises from the structural changes and the overall polarizability (optical basicity). Refractive index, molar refractivity Rm and molar polarizability αm values increase with increasing optical basicity of the glasses. The characteristic absorption peaks of Sm3+ were also investigated. For Sm/Ce co-doped glasses, especially at high concentration of CeO2, the absorption of Ce3+ hinders the high energy absorption of Sm3+ and this effect becomes more obvious with increasing optical basicity.