Structural and optical properties of Er³⁺ doped SiO₂–Al₂O₃–GeO₂ compounds prepared by a simple route

Highlights: • We developed a simple route to obtain gels and powders using GeO₂, TEOS and TMAH solution. • Al₆Ge₂O₁₃ crystalline nanoparticles embedded in amorphous matrix were obtained. • The Al₂O₃ enhance Er³⁺ dispersion in GeO₂–SiO₂ increasing its emission and the full width at half maximum from 41 to 56 nm. • The ⁴I_13/2 Er³⁺ level lifetime varies between 4.8 and 5.6 ms (1533 nm emission). - Abstract: Samples of (1 − x)[0.70SiO₂ + 0.30Al₂O₃] + xGeO₂ compositions, containing x = 0.05, 0.10, 0.20, 0.30, 0.40 and 0.50, and doped with 1 mol% of Er³⁺, were prepared by a mixed route (sol–gel process and Pechini method). Transparent gels were synthesized and homogeneous powders were obtained by heat treatments from 800 °C to 1050 °C. The final powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and high-resolution transmission electron microscopy. The optical properties were studied by photoluminescence measurements in the infrared region, and the average lifetime of the metastable state ⁴I_13/2 of Er³⁺ ions and the full-width at half maximum (FWHM) were determined. A silica-rich amorphous phase and nanocrystallites with orthorhombic structure of Al₆Ge₂O₁₃ phase were obtained. The samples present a broad emission centered at around 1532 nm under excitation at 977 nm, with a FWHM of 53 nm and a lifetime of 5.6 ms. The synthesized compounds by an easy chemical procedure are potentially applicable in integrated optical systems