Effect of TiO2 on thermal, structural and third-order nonlinear optical properties of Ca–La–B–O glass system

A series of calcium lanthanum metaborate glasses in the composition (wt%) of 23.88CaO–28.33La2O3–47.79B2O3 modified with TiO2 up to 20 wt% are prepared by a melt quenching technique to study the influence of TiO2 on their thermal, structural, linear and nonlinear optical properties. The differential thermal analysis (DTA) studies have demonstrated significant effects due to the presence of TiO2 on the glass forming ability and crystallization situations. The glass with 15 wt% TiO2 has achieved a eutectic composition and also exhibited a better glass forming ability among the glasses studied. The FT-IR spectra of these glasses show mainly vibration modes corresponding to stretching of BO3 trigonal, BO4 tetrahedral units and of B–O–B bending bonds. At higher concentrations of TiO2, development of vibration band around 400 cm−1 has indicated the formation of TiO6 structural units in the glass network. The red shift of optical absorption edge (UV cutoff) shows a monotonous decrease in direct and indirect optical band gap energies (Eopt) with an increase of TiO2 content in the glasses based on their absorption spectra. The optical transparency of these glasses is found to be varied from 64 to 87% within the wavelength range 450–1100 nm depending on the TiO2 content. Besides these studies, linear refractive indices, the nonlinear optical properties of these glasses have also been evaluated.