Spherical core–shell structured nanophosphors on the basis of europium-doped lutetiumcompounds

Abstract

Crystalline Lu2O3:Eu3+ nanolayers with a europium content from 1 to 10 at.% were immobilized onto amorphousSiO2 submicrospheres by a sol–gel technique, forming monodisperseSiO2/Lu2O3:Eu3+ core–shell structured nanophosphors. The nanostructure, morphology and composition of thecore–shell particles obtained were investigated by transmission electron microscopy (TEM),energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), Fouriertransform infrared spectroscopy (FT-IR) and x-ray diffraction (XRD) techniques. TheLu2O3 nanolayers are found to begin to crystallize on theSiO2 cores at500 °C and a solid-phasereaction between the Lu2O3 and SiO2 componentsoccurs at 1000 °C. phase transitions in the core–shell particles were observed at temperatures ranging from1000 to1200 °C. Underx-ray excitation, europium-doped core–shell nanophosphors are characterized by effective luminescencein the λ = 575–725 nm range corresponding to transitions (J = 0–4) of Eu3+ ions. It has been shown that the radioluminescence intensity of theheterostructures strongly depends on the annealing temperature, the numberof coated layers and the dopant concentration. The radioluminescence of theSiO2/Lu2O3:Eu3+ heterostructures coated with a protective undopedLu2O3 shell is higher than in the case of the unprotectedSiO2/Lu2O3:Eu3+ core–shell phosphors. The possible reasons for such a phenomenon are also discussed.