Morphological, structural, optical and dielectric properties of 91SiO2:4Li2O:4Nb2O5:1Dy2O3 (% mole) glass prepared by sol-gel

Abstract

We report on the structural, morphological and optical characterization of glass and glass-ceramic samples, with nominal composition of 91SiO2:4Li2O:4Nb2O5:1Dy2O3 (% mole). The samples were heated treated in air in the temperature range between 500 °C and 800 °C. The glass-ceramics samples start to crystallize at temperatures above 600 °C and besides the SiO2 and LiNbO3 crystalline phases, sub micron DyNbO4 precipitates were identified by X-ray diffraction and scanning electron microscopy for temperatures above 750 °C. Using Raman spectroscopy was possible to identify the vibration modes assigned to the crystalline phases detected by the XRD analysis. Also, the performed Photoluminescence Spectroscopy analysis suggest that the optical activation of Dy3+ ions in the glass and glass-ceramics hosts was found to be dependent of the heat treatment temperature. Intraconfigurational transitions between the 4F9/2 and 6HJ(=15/2, 13/2) multiplets of Dy3+ ions were only observed for samples without the presence of the DyNbO4 crystalline phase. Moreover, for samples heat treated between 500 °C and 700 °C the intensity ratio of the 4F9/26H13/2 and 4F9/26H15/2 transitions of the lanthanide ion changes, suggesting different ion environments which are dependent on the thermal annealing temperature. The dielectric measurements revealed that ε′ value depends mainly in the number of network modifier ions and the relaxation phenomenon observed at frequencies above 10 kHz, in all samples, can be assigned to the increase of the volume ratio between the LiNbO3 particles and the glass network