Er3+-doped SiO2–Al2O3 thin films prepared by the sol–gel route

The synthesis of homogeneous and pure silica–alumina binary glasses doped with rare-earth (RE) ions such as Er3+ is currently a key challenge for the development of integrated optics devices such as lasers, optical amplifiers or waveguides. In this study Er3+-doped SiO2–Al2O3 films were prepared by the sol–gel route. Aluminium sec-butoxide, Al(O-sec-C4H9)3 (ASB), and tetraethoxysilane, Si(OC2H5)4 (TEOS), were used as glass oxide precursors, whereas erbium was introduced as Er(NO3)3. The alumina content in the silica matrix was 10 at.%, while erbium doping ranged between 200 and 5000 ppm. The preparation of the starting sol–gel solution and the layer deposition by a dip-coating procedure were performed in dry-box under nitrogen atmosphere. The obtained films were subsequently annealed in air between 300 and 1000 °C. After treatment at 500 °C, layers 200 nm thick were obtained. The composition, microstructure and surface morphology of the films were investigated by X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), glancing incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). Crack-free, transparent, high purity films were obtained, characterised by compositional and microstructural homogeneity.