Structural and optical properties of 60B2O3–(20−x)Na2O–10PbO–10Al2O3:xTiO2:yNd2O3 glasses

• Investigation of the BO4 to BO3 back conversion effect in borate glasses.
• The influence of the substitution of Na2O by TiO2 on the Nd2O3 optical properties.
• Investigation of the structural properties of rare earth doped borate glasses.

In this work we investigate the effect of replacing Na2O by TiO2 on the structural and spectroscopic characteristics of the Nd2O3-doped 60B2O3–(20−x)Na2O–10PbO–10Al2O3:xTiO2:yNd2O3 borate glass matrix. Measurements of X-ray patterns, glass temperatures (Tg), vibrational (Raman and infrared (IR)) and optical (absorption and emission) spectra were carried out. The trend of Tg, the Judd–Ofelt parameters and Nephelauxetic ratio as the TiO2 and Nd2O3 concentration increases was interpreted quantitatively and qualitatively in terms of the network bonds and coordination numbers. Measurements of Tg across the Nd-doped glass series for different levels of Ti suggests changes in the rigidity of the matrix due to change of coordination of boron oxide resulting from the BO4–BO3 back conversion effect. The changes observed in the Raman and IR spectra are related to the BO3 → BO4 conversion effect. The variation of the Judd–Ofelt parameters Ω(2)Ω(2) and Ω(6)Ω(6) indicates that the average rare earth-ligand radius decreases establishing an electronic density distribution when Nd3+ concentration increases. This effect is interpreted in terms of Judd–Ofelt parameters and by the bonding parameter b1/2b1/2 due to Nephelauxetic effect.