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.

A search for double β decay of dysprosium was realized for the first time with the help of an ultra-low background HP Ge γ detector. After 2512 h of data taking with a 322 g sample of dysprosium oxide limits on double beta processes in 156Dy and 158Dy have been established on the level of T⩾1014-1016 yr. Possible resonant double electron captures in 156Dy and 158Dy were restricted on a similar level. As a by-product of the experiment we have measured the radioactive contamination of the Dy2O3 sample and set limits on the α decay of dysprosium isotopes to the excited levels of daughter nuclei as T⩾1015-1017 yr

Y2O3:Yb3+ 5 at% ceramics have been synthesized by the reactive sintering method using different commercial yttria powders (Alfa-Micro, Alfa-Nano, and ITO-V) as raw materials. It has been shown that all Y2O3 starting powders consist from agglomerates up to 5–7 µm in size which are formed from 25–60 nm primary particles. High-energy ball milling allows to significantly decreasing the median particle size D50 below 500 nm regardless of the commercial powders used. Sintering experiments indicate that powder mixtures fabricated from Alfa-Nano yttria powders have the highest sintering activity, while (Y0.86La0.09Yb0.05)2O3 ceramics sintered at 1750 °C for 10 h are characterized by the highest transmittance of about 45%. Y2O3:Yb3+ ceramics have been obtained by the reactive sintering at 1750–1825°C using Alfa-Nano Y2O3 powders and La2O3+ZrO2 as a complex sintering aid. The effects of the sintering temperature on densification processes, microstructure, and optical properties of Y2O3:Yb3+ 5 at% ceramics have been studied. It has been shown that Zr4+ ions decrease the grain growth of Y2O3:Yb3+ ceramics for sintering temperatures 1750–1775 °C. Further increasing the sintering temperature was accompanied by a sharp increase of the average grain size of ceramics referred to changes of structure and chemical composition of grain boundaries, as well as their mobility. It has been determined that the optimal sintering temperature to produce high-dense yttria ceramics with transmittance of 79%–83% and average grain size of 8 µm is 1800 °C. Finally, laser emission at ∼1030.7 nm with a slope efficiency of 10% was obtained with the most transparent Y2O3:Yb3+ 5 at% ceramics sintered.

No abstract

No abstract