Sol-gel (chitosan-mediated) synthesis of europium-doped zinc (clay, silicate and sulphide) for light emitting applications

Abstract

This study reports the sol-gel (chitosan-mediated) synthesis of europium-doped zinc silicates from a cheap and locally available clay (Eu:Znclay), commercial silica(Eu:ZnSiO3)  as well as zinc sulphide (ZnS) for light emitting applications. This was done to provide alternative and cheaper silica source for the same purpose while ZnS was used as a known phosphor. The samples were synthesized from their nitrate salts using a sol-gel (chitosan-mediated) route and characterized with PXRD, SEM, UV-Vis and FT-IR. The PXRD results showed that reflections from Eu:Znclay matched with thoer was less crystalline with lower peak intensities. The ZnS reflection pattern on the other hand matched with the wurtzite ZnO/ZnS crystal structures indicating a mixed phase material. Particle size estimations from XRD data were 68.86, 70.35 and 68.05 nm for Eu:Znclay, Eu:ZnSiO3 and Eu:ZnS respectively. The SEM micrographs also showed more scattered polycrystallites in those of Eu:Znclay and Eu:ZnS than in Eu:ZnSiO3. The FT-IR spectra showed that both samples had the four characteristic symmetrical and asymmetrical Si-O-Si stretching and bending  modes around 466, 693, 777 and 1097 cm-1 in Eu:Znclay and 463, 694, 778 and 1075 cm-1 in Eu:ZnSiO3 respectively with higher intensities for Eu:ZnSiO3 bands.. The UV-Vis spectra of Eu:Znclay and Eu:ZnSiO3 showed weak bands at 248, 296 nm and a strong broad band at (490-505) and (487-496) nm attributed to emission due to 5D0 →7F1-3 Eu3+transitions while the bands of Eu:ZnS were at 296 nm, a  long gap between 340-482 nm and a λmax at 761 nm. The slight red shift and more light scattering (smaller sizes) observed for Eu:Znclay indicated better light emitting properties over the conventional Eu:ZnSiO3.Keywords: Chitosan, Europium-doped-metal, Clay, Silicate, Sulphide%2-metal, Clay, Silicate, Sulphide, Phosphors.