title: Spherical core-shell structured nanophosphors on the basis of europium-doped lutetium compounds.
abstract: Crystalline Lu(2)O(3):Eu(3+) nanolayers with a europium content from 1 to 10 at.% were immobilized onto amorphous SiO(2) submicrospheres by a sol-gel technique, forming monodisperse SiO(2)/Lu(2)O(3):Eu(3+) core-shell structured nanophosphors. The nanostructure, morphology and composition of the core-shell particles obtained were investigated by transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and x-ray diffraction (XRD) techniques. The Lu(2)O(3) nanolayers are found to begin to crystallize on the SiO(2) cores at 500 degrees C and a solid-phase reaction between the Lu(2)O(3) and SiO(2) components occurs at 1000 degrees C. Lu(2)O(3) --> Lu(2)SiO(5) --> Lu(2)Si(2)O(7) phase transitions in the core-shell particles were observed at temperatures ranging from 1000 to 1200 degrees C. Under x-ray excitation, europium-doped core-shell nanophosphors are characterized by effective luminescence in the lambda = 575-725 nm range corresponding to (5)D(0) --> (7)F(J) transitions (J = 0-4) of Eu(3+) ions. It has been shown that the radioluminescence intensity of the heterostructures strongly depends on the annealing temperature, the number of coated layers and the dopant concentration. The radioluminescence of the SiO(2)/Lu(2)O(3):Eu(3+) heterostructures coated with a protective undoped Lu(2)O(3) shell is higher than in the case of the unprotected SiO(2)/Lu(2)O(3):Eu(3+) core-shell phosphors. The possible reasons for such a phenomenon are also discussed.
authors.affiliation: Scientific and Technological Corporation Institute for Single Crystals, NAS of Ukraine, Kharkov, Ukraine. yermolayeva@isc.kharkov.ua
authors.forename: Yu V
authors.initials: YV
authors.lastname: Yermolayeva
authors.forename: A V
authors.initials: AV
authors.lastname: Tolmachev
authors.forename: T I
authors.initials: TI
authors.lastname: Korshikova
authors.forename: R P
authors.initials: RP
authors.lastname: Yavetskiy
authors.forename: M V
authors.initials: MV
authors.lastname: Dobrotvorskaya
authors.forename: N I
authors.initials: NI
authors.lastname: Danylenko
authors.forename: D S
authors.initials: DS
authors.lastname: Sofronov