Optical properties of Er-doped Al2O3-SiO2 films prepared by a modified sol-gel process

Er-doped Al2O3-SiO2 (1/9 in mol ratio of Al2O3/SiO2) thin films were prepared by using a modified sol-gel process. The modified process entails the precipitation and digestion of Er(OH)3, obtained from the reaction between Er ions and NH4OH in solution. Thin films were deposited on Si wafers by using a spin coating technique (3000 rpm) and the coated films were heat treated at different temperatures for 1 h in an oxygen-purged furnace. All the films were structurally characterized by the X-ray diffraction technique using CuK alpha radiation. Refractive indices and the morphologies of the films were studied using a spectroscopic phase modulated ellipsometer and atomic force microscopy, respectively. It was observed that the films were crack free and of about 0.4 mu m thickness in a single spin coating and both the lifetime and the photoluminescence intensity of Er ions increased with increasing the annealing temperature. The luminescence properties of the Er-doped Al2O3-SiO2 made by a conventional and our modified doping process were compared and discussed from the stand point of peak intensities and lifetimes as a function of annealing temperatures. It is to be noted here that our modified process was found to be more effective in reducing the clustering of Er ions in Al2O3-SiO2 materials as compared to that of the conventional method.