Optical properties of Ho3Â + in sol-gel silica glass co-doped with Aluminium

Ho3 + in SiO2 glass samples co-doped with Aluminium at different concentrations have been synthesized by sol-gel method. The Judd-Ofelt parameters Ω2, Ω4 and Ω6 were obtained from the absorption spectra in the visible region and the value of Ω2 increases in the presence of Aluminium. Photoluminescence emissions in the visible region at 492, 550, 662 and 756 nm were observed under 450 nm excitation. In addition to the overall luminescence enhancement, selective enhancement of the 550 and 756 nm emissions was observed in the presence of Aluminium. The selective enhancement was observed only after annealing above 950 °C. The results obtained show the lowering of site symmetry of the Ho3 + ions as well as the reduction in cross-relaxation in the presence of Aluminium.