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Ivantsov Ruslan D.,Lin Chun-Rong,Ivanova Oxana S.,Altunin Roman R.,Knyazev Yuriy V.,Molokeev Maxim S.,Zharkov Sergey M.,Chen Ying-Zhen,Lin En-Szu,Chen Bing-Yi,Shestakov Nikolai P.,Edelman Irina S. 한국물리학회 2021 Current Applied Physics Vol.25 No.-
Greigite (Fe3S4) nanoparticles (NPs) were fabricated by the thermal decomposition method using two different surfactants: oleylamine (OLA) and 1-hexadecylamine (HDA). In both cases, the synthesized NPs were characterized as the Fe3S4 nanocrystals with minor inclusions of Fe9S11 phase. FT-IR spectroscopy and thermogravimetric analysis allow concluding about OLA or HDA shells covering magnetic core of NPs. M¨ossbauer spectra has revealed deviations of iron ions distribution among crystal positions from that presented in literature for pure greigite. In accordance with these deviations, the pronounce changes are observed in the magnetic circular dichroism (MCD) spectra which manifest themselves as the spectrum shift to higher energies of electromagnetic waves and redistribution of the MCD maximum intensities. These effects are associated with a change in the density of electronic states in the samples due to the redistribution of iron ions between octahedral and tetrahedral positions in nanocrystals under the influence of surfactants.
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.
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>
The Vis-NIR multicolor emitting phosphor Ba4Gd3Na3(PO4)6F2: Eu2+, Pr3+ for LED towards plant growth
Ziwei Zhou,Niumiao Zhang,Jiayu Chen,Xianju Zhou,Maxim S. Molokeev,Chongfeng Guo 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.65 No.-
Photosynthesis process is the basic for plant growth, which needs energy from the light. The pigments of chlorophyll a, b and bacteriochlorophyll are responsible for the absorption of light, in which blue, red and near-infrared (NIR) light directly or indirectly promote the plant growth and enhancement of nurtiments. It is important for plant to support absorbable light, and phosphhor-converted light emitting diodes (pc-LEDs) are low-cost, energy-saving and enviromental friendly devices for plant growth. To develop a phosphor with emission covering the blue, red and NIR, a series of phosphors Ba4Gd3Na3(PO4)6F2: Eu2+, Pr3+ with blue, red and NIR multi-emitting were prepared. Their emissions not only match well with the absorption spectra of pigments in the plant, but also could be excited by near ultraviolet (n-UV) LED chip. The crystal structure of host Ba4Gd3Na3(PO4)6F2 was refined from the XRD data and three different crystallographic sites occupied by Eu2+ were determined through low temperature photoluminescence spectra. The energy transfer from Eu2+ to Pr3+ ions was also discussed in detail. Results indicated that the multi-emitting Ba4Gd3Na3(PO4)6F2: Eu2+, Pr3+ can serve as a phosphor candidate for plant growth LEDs.