Erbium-activated silica xerogels: spectroscopic and optical properties

Silica-based sol–gel glasses activated by Er³⁺ ions are attractive materials for integrated optics (IO) devices such as frequency upconverters and optical amplifiers. Monolithic erbium-activated silica xerogels with erbium content ranging from 0 up to 40 000 ppm were prepared by the sol–gel technique. Samples were densified by thermal treatment in air at 950°C for 120 h. The densification degree and the relative content of hydroxyl groups were studied by Raman spectroscopy. Refractive indices were measured at 632.8 and 543.5 nm by a prism coupling technique. Green to blue and violet upconversion luminescence upon continuous-wave excitation at 514.5 nm was observed for all samples. Emission at 1.5 μm, characteristic of the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ ions, was observed at room temperature for all samples upon continuous-wave excitation at 980 nm. For the 5000 Er/Si ppm-doped xerogel, a photoluminescence was observed and a lifetime of 8 ms for the metastable ⁴I_13/2 level was measured.