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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.
Lim, Chang Sung,Aleksandrovsky, Aleksandr S.,Molokeev, Maxim S.,Oreshonkov, Aleksandr S.,Atuchin, Victor V. ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.713 No.-
<P><B>Abstract</B></P> <P>Ternary scheelite-type molybdate NaSrLa<SUB>(1-<I>x</I>-<I>y</I>)</SUB>(MoO<SUB>4</SUB>)<SUB>3</SUB>:<I>x</I>Er<SUP>3+</SUP>,<I>y</I>Yb<SUP>3+</SUP> (<I>x</I> = <I>y</I> = 0, <I>x</I> = 0.1 and <I>y</I> = 0.2, <I>x</I> = 0.05 and <I>y</I> = 0.45, <I>x</I> = 0.2 and <I>y</I> = 0) phosphors were successfully synthesized by the microwave sol-gel method for the first time. Well-crystallized particles formed after the heat-treatment at 900 °C for 16 h showed a fine and homogeneous morphology with a particle size of 2–3 μm. The crystal structures were refined by the Rietveld method in space group <I>I</I>4<SUB>1</SUB>/<I>a</I>. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under the excitation at 980 nm, the NaSrLa<SUB>0.7</SUB>(MoO<SUB>4</SUB>)<SUB>3</SUB>:0.1Er<SUP>3+</SUP>,0.2Yb<SUP>3+</SUP> and NaSrLa<SUB>0.5</SUB>(MoO<SUB>4</SUB>)<SUB>3</SUB>:0.05Er<SUP>3+</SUP>,0.45Yb<SUP>3+</SUP> particles exhibited a strong 525-nm emission band, a weaker 550-nm emission band in the green region and weak 655-nm, 490-nm and 410-nm emission bands in the red, blue and violet regions. The pump power dependence and Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail. The presence of Sr in NaSrLa(MoO<SUB>4</SUB>)<SUB>3</SUB>, in comparison with NaCaLa(MoO<SUB>4</SUB>)<SUB>3</SUB> compound, leads to frequency shift mainly in the low region of Raman spectra. The MoO<SUB>4</SUB> bending vibrations are most susceptible to changes in the distance between the nearest oxygen atoms in the nearest neighboring MoO<SUB>4</SUB> groups.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The NaSrLa(MoO<SUB>4</SUB>)<SUB>3</SUB>:Er<SUP>3+</SUP>,Yb<SUP>3+</SUP> phosphors were synthesized by the microwave method. </LI> <LI> The crystal structures were refined by the Rietveld method in space group <I>I</I>4<SUB>1</SUB>/<I>a</I>. </LI> <LI> Under the excitation at 980 nm, a strong green emission is observed in the phosphors. </LI> </UL> </P>
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.