White-Light and Yellow/Blue Photoluminescence Emission Based on Dy3+-Doped SiO2–Gd2O3 Composites

Abstract

This work attempts to obtain Dy3+-doped SiO2–Gd2O3 by sol–gel process, with a molar ratio of 70Si4+–30Gd3+ and Dy3+ concentrations of 0.1, 0.3, 0.5, and 1 mol%. Heat treatment at temperatures of 1000°C, 1100°C, 1200°C, and 1300°C have been performed. From XRD, the Gd2O3 cubic phase was observed at 1000°C and 1100°C, at 1200°C also were observed Gd2O3 monoclinic phase, predominant at 1300°C. The band-gap values vary between 4.4 and 5.3 eV, showing dependence on the crystalline phase. Under UV excitation, emission spectra show bands assigned to the Dy3+ transitions: 4F9/2→6H15/2 (484 nm), 4F9/2→6H13/2 (572 nm), and 4F9/2→6H11/2 (668 nm). The excitation at 275 nm has shown more effective. The ratio between the most intense emission bands (yellow/blue) show values around 0.84 and 1.63. CIE chromaticity diagrams show color coordinates at blue, yellow, and white regions, as a function of Dy3+ concentration and heat treatment. The lifetime values of excited state 4F9/2 were around 0.20 and 0.69 ms. The morphology of particles changed from spherical to coral-like shape as a function of heat treatment are observed. The sol–gel process showed to be an interesting route to obtain Dy3+-doped binary system materials.