Physical and optical properties of Nd³⁺ co-doped Al in sol–gel silicate glasses

The optical properties of varying concentrations of Nd3 + ions co-doped with Al in the chemical compositions (80-x)SiO₂ + 20Al₂O₃ + xNdF₃ (SiAlNd), where x = 0.6, 1.2, 1.8, and 2.4 mol%, were investigated using the sol–gel method. Structural characterization was carried out using XRD and FTIR techniques. It was found that the polarizability of oxide ions increased with the concentration of rare earth ions, as evidenced by the observed values of density, refractive index, and Nd³⁺ ion concentration in the glasses. Even after heating to 800 °C, XRD results indicated that the prepared glass samples remained amorphous. FTIR was employed to identify the functional groups present in the synthesized sol–gel silica glass. The UV–Vis-NIR absorption spectra revealed seven peaks, corresponding to the excitation of electrons from the ground state ⁴I_9/2 to ⁴G_9/2 (~ 513 nm), ⁴G_7/2 (~ 528 nm), ⁴G_5/2 + ²G_7/2 (~ 585 nm), ²H_11/2 (~ 622 nm), ⁴F_9/2 (~ 684 nm), ⁴F_7/2 + ⁴S_3/2 (~ 747 nm), ⁴F_5/2 + ²H_9/2 (~ 807 nm), and ⁴F_3/2 (~ 878 nm). The Judd–Ofelt intensity parameters were derived from the absorption spectra of Nd³⁺-co-doped alumino-silicate glass. The fluorescence properties were also examined by assessing the radiative lifetime (τ_R), luminescence branching ratio (β_R), and spontaneous transition probability (A_R).