Influence of the synthesis conditions of Y0.9Dy0.1VO4 and silica-coated Y0.9Dy0.1VO4 nanophosphors on the powder morphology and luminescence emission intensity

Abstract

Y0.9Dy0.1VO4 nanophosphors were prepared by a sol-gel process and a hydrothermal synthesis at different pH values of the reaction medium. Samples prepared by hydrothermal synthesis at pH = 2 were also coated with silica. All obtained samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), micro-Raman, and micro-photoluminescence (PL). XRD patterns of Y0.9Dy0.1VO4 samples show diffraction maxima which can be indexed to a tetragonal symmetry of space group I41/amd with Z = 4, compatible with a zircon-type structure. A higher intensity of the XRD maxima is observed in patterns of samples prepared by the sol-gel method at acid pH. TEM images reveal that the particle morphology and size, ranging from 20 to 45 nm in the different nanophosphors, depend on the preparation method and the synthesis conditions. Raman and FTIR spectra of the samples have been correlated with XRD results. An increased thickness of the silica coating is observed in TEM images as the reaction time with tetraethyl orthosilicate (TEOS) increases. The presence of silica is also evidenced by FTIR absorption spectra. The different synthesis routes modify the overall PL intensity, as well as the relative weight of the dominant blue and yellow emissions characteristics of Dy3+ ions. An enhanced PL emission intensity has been found in samples coated with silica, which can be attributed to a reduction of surface defects.