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High-temperature oxidation of europium (II) sulfide
Yuriy G. Denisenko,Maxim S. Molokeev,Alexander S. Krylov,Aleksandr S. Aleksandrovsky,Aleksandr S. Oreshonkov,Victor V. Atuchin,Nikita O. Azarapin,Pavel E. Plyusnin,Elena I. Sal’nikova,Oleg V. Andreev 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.79 No.-
The process of high-temperature oxidation of EuS in the air was explored in the temperature range of500–1000 C. The oxidation reaction enthalpy was determined (DH0exp =1718.5 kJ/mol). The study ofoxidation products allowed to establish the mechanism of EuS oxidation with oxygen. At 500–600 C, EuSis oxidized to a mixture of Eu3+-containing compounds (Eu3S4, Eu2O2S). In the range of 700–1000 C, onlyeuropium oxysulfate Eu2O2SO4 is formed. The structure refinement for Eu2O2SO4 was performed by theRietveld method. The luminescence intensity of europium oxysulfate Eu2O2SO4 with characteristic 4f-4ftransitions from the 5D0 state was investigated as a function of oxidation temperature.
Synthesis and luminescence properties of β-NaRE0.95Eu0.05F4 (RE¼Y, Lu)
Illariia A. Razumkova,Alexander E. Sedykh,Yuriy G. Denisenko,Klaus Müller-Buschbaum 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.92 No.-
On the base of β-NaYF4 and β-NaLuF4 compounds, optimal synthesis methods were selected to obtainhighly crystalline Eu3+-doped compounds in the hexagonal (β) structure. The compounds β-NaY0.95Eu0.05F4 and β-NaLu0.95Eu0.05F4 were synthesized by hydrothermal synthesis. The concentrationof Na2EDTA introduced into the reaction system as a modifier affects the shape and size of the productfrom elongated hexagonal prisms to quartz-like crystals. The thermal behavior of the compounds hasbeen studied; the temperature of the polymorphic transition from hexagonal to cubic structure is 680 Cfor β-NaY0.95Eu0.05F4 and 624 C for β-NaY0.95Eu0.05F4, the melting point of α-NaRE0.95Eu0.05F4 is about900 C. Under excitation with UV-light of l = 393 nm, β-NaY0.95Eu0.05F4 and β-NaLu0.95Eu0.05F4 show theemission lines of direct Eu3+ f-f transitions, with the presence of the emission from higher Eu3+ excitedstates (up to 5H3) in both samples, which is responsible for the more orange color of emission instead ofthe usual red for Eu3+. Emission decay times are slightly longer for β-NaY0.95Eu0.05F4 than for β-NaLu0.95Eu0.05F4, which is the result of a bigger unit cell for the former, leading to longer interatomicdistances between Eu3+ ions in the lattice. The luminescence mechanisms for the doped lanthanide ionswere thoroughly analyzed.
Lim, Chang Sung,Atuchin, Victor V.,Aleksandrovsky, Aleksandr S.,Denisenko, Yuriy G.,Molokeev, Maxim S.,Oreshonkov, Aleksandr S. Materials Research Society of Korea 2019 한국재료학회지 Vol.29 No.12
New triple tungstate phosphors NaPbLa(WO<sub>4</sub>)<sub>3</sub>:Yb<sup>3+</sup>/Ho<sup>3+</sup> (x = Yb<sup>3+</sup>/Ho<sup>3+</sup> = 7, 8, 9, 10) are successfully fabricated by microwave assisted sol-gel synthesis and their structural and frequency upconversion (UC) characteristics are investigated. The compounds crystallized in the tetragonal space group I4<sub>1</sub>/a and the NaPbLa(WO<sub>4</sub>)<sub>3</sub> host have unit cell parameters a = 5.3927(1) and c = 11.7961(3) Å, V = 343.05(2) Å<sup>3</sup>, Z = 4. Under excitation at 980 nm, the phosphors have yellowish green emissions, which are derived from the intense <sup>5</sup>S<sub>2</sub>/<sup>5</sup>F<sub>4</sub>→<sup>5</sup>I<sub>8</sub> transitions of Ho<sup>3+</sup> ions in the green spectral range and strong <sup>5</sup>F<sub>5</sub>→<sup>5</sup>I<sub>8</sub> transitions in the red spectral range. The optimal Yb<sup>3+</sup>:Ho<sup>3+</sup> ratio is revealed to be x = 9, which is attributed to the quenching effect of Ho<sup>3+</sup> ions, as indicated by the composition dependence. The UC characteristics are evaluated in detail under consideration of the pump power dependence and Commission Internationale de L'Eclairage chromaticity. The spectroscopic features of Raman spectra are discussed in terms of the superposition of Ho<sup>3+</sup> luminescence and vibrational lines. The possibility of controlling the spectral distribution of UC luminescence by the chemical content of tungstate hosts is demonstrated.