Effects of SiO2 coating on luminescence property and thermostability of Sr2MgSi2O7: Eu2+, Dy3+ phosphors

Abstract

Sr2MgSi2O7: Eu2+, Dy3+ phosphor powders are unstable and degrade at elevated temperature, thus limiting their applications in the medium to high temperature range. To prevent or minimize this degradation, a SiO2 coating on the surface of Sr2MgSi2O7: Eu2+, Dy3+ phosphors was prepared using a sol–gel method with tetraethyl orthosilicate (TEOS) precursor. The phosphor powder samples were characterized by X-ray diffraction, Fourier Transform infrared spectroscopy, transmission electron microscope, scanning electron microscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. The transmission electron microscope and scanning electron microscopy images show that the SiO2 nano-layer was uniformly formed on the surface of the phosphors, and the thickness of the SiO2 coating is about 8.4 nm. The X-ray diffraction and Fourier Transform infrared spectroscopy analysis indicated that the crystal phase did not change after the coating. The experimental results show that the photoluminescence intensity of the SiO2-coated phosphors is 23 % higher than that of uncoated phosphors. In addition, when the annealing temperature is below 1100 °C, the SiO2-coated phosphors show better thermostability than that of the uncoated phosphor due to the coating acts as a protective layer that can retard oxygen diffusion into the phosphors thus preventing oxidation of the Eu2+ ions. Surface modification of the Sr2MgSi2O7: Eu2+, Dy3+ phosphors by SiO2 coating is an effective way to improve photoluminescence intensity and thermostability of the Sr2MgSi2O7: Eu2+, Dy3+ phosphors. Emission spectra of uncoated and SiO2-coated phosphors under 365 nm excitation