Synthesis of new non-covered and silica-covered Y0.9Tm0.1-xYbxVO4 nanophosphors with emission in the visible and NIR ranges

Abstract

The development of new materials of interest in the bioimaging field is a relevant topic in current research. We present and study here novel non-covered and silica-covered Y0.9Tm0.1-xYbxVO4 samples with x = 0, 0.01, 0.05 and 0.09 that were prepared by hydrothermal synthesis. For comparison purposes, the study of Y0.9Tm0.1VO4 sample synthesized by the sol-gel method was also included. The relationships between the synthesis method, dopant content and luminescence emission were systematically studied by X-ray diffraction (XRD), FTIR spectroscopy and transmission electron microscopy (TEM). XRD profiles and FTIR spectra confirm the zircon-type structure of the obtained samples. Particles of two different morphologies were found in TEM images of uncoated samples, some spherical with sizes between 42 and 50 nm and others elongated. A shell thickness between 8 and 13 nm was also observed in silica-covered samples. Photoluminescence studies of our samples revealed emission in the NIR and visible ranges. Under excitation at 790 nm, the spectra of thulium-doped samples showed the characteristic emission band of Tm3+ ions. Substitution of thulium by ytterbium successfully led to an up-conversion emission under excitation at 980 nm. Finally, the fluorescent emission study in the NIR of samples that could be more biocompatible demonstrated that they are suitable for use as luminescent thermometers in the physiological temperature range.