Fabrication of highly concentrated Er³⁺ doped aluminosilicate films via sol-gel processing

Optically active highly concentrated Er³⁺-Al³⁺ codoped silica thin films were fabricated on fused silica substrates by sol-gel method. The synthesis of the Er³⁺-Al³⁺ double alkoxide was intended to prevent the optically harmful Er clustering by the selective coordination of Al³⁺ around Er³⁺ ions. The molar Er ion concentration was varied from 3811 to 23719 ppm. Photoluminescence (PL) measurements indicated that Er ions were optically active in all films of different Er concentrations. A broadband peak was observed at 1531 nm with the full width at half-maximum (FWHM) of 42 nm, which corresponds to the ⁴I_13/2→⁴I_15/2 transition. The shape, peak position, and FWHM of the PL signals from the sol-gel derived Er³⁺ doped silica were quite comparable to those prepared by other methods. The PL peak showed maximum intensity at an Er concentration of 8535 ppm. This implies the concentration quenching at higher Er concentrations.