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[en] Terbium doped strontium yttrium borate phosphor is prepared by solution combustion method. Structural characterization of Sr3Y(BO3)3:Tb3+ (SYB:Tb) has been carried out with X-ray powder diffraction (XRD) analysis. Particle size of 0.5–2 μm and perfect element composition were seen in SEM-EDS. Using FTIR at room temperature the presence of (BO3)- group; complete combustion of nitrates, organic material, absence of O-H bond were firmed up. Photoluminescence properties of the phosphor have been investigated by measuring the excitation and emission spectra. Several luminescence bands of Tb3+ ions are observed under 233 nm excitation wavelengths in 350–700 nm spectral region. The emission spectra were composed of three bands, in which the dominated emission of green luminescence SYB:Tb attributed to the transition 5D4→7F5 is centered at 543 nm. The dependence of the emission intensity on the Tb3+ concentration for the Sr3Y1-x(BO3)3:xTb3+ (0.01 ≤ x ≤ 0.05) was studied and observed that the optimum concentration of Tb3+ in phosphor was 3 mol% for the highest emission intensity at 543 nm. The CIE coordinates (X=0.251363409, Y=0.736605581) fall at the border of green region in the CIE 1931 chromaticity. (author)
[en] We measure the electrical resistivity and Hall effect of alkaline-earth-metal hexaboride single crystals as a function of temperature, hydrostatic pressure, and magnetic field. The transport properties vary weakly with the external parameters and are modeled in terms of intrinsic variable-valence defects. These defects can stay either in (1) delocalized shallow levels or in (2) localized levels resonant with the conduction band, which can be neutral or negatively charged. Satisfactory agreement is obtained for electronic transport properties in a broad temperature and pressure range, though fitting the magnetoresistance is less straightforward and a combination of various mechanisms is needed to explain the field and temperature dependences.
[en] The aim of this project was to develop an analytical method for the analysis of five of the platinum group metals and gold already present in aqueous solutions of variable and mostly unknown matrices
[en] Sm2+-doped strontium borophosphate, Sr6BP5O20, was prepared by high-temperature solid-state reaction method. The photoluminescence excitation and emission spectra together with the decay curves of Sm2+ ions were investigated from 10 to 300 K. The emission arises from the 5D0 level of Sm2+ ions. The investigations were focused mainly on the distribution of Sm2+ sites in Sr6BP5O20 crystal, which exhibits different spectroscopic features. There exist two isolated Sm2+ crystallographic sites in Sr6BP5O20 at low temperature (10 K), where no energy transfer could be detected. Only one Sm2+ site could be detected at high temperature above 100 K. Luminescence and microstructure of Sm2+ ions were discussed based on the structure of Sr6BP5O20 crystal.
[en] Two new intermetallic alkaline-earth palladium borides, SrPd_4B and BaPd_4B were synthesised and their physical properties were investigated. The crystal structure of SrPd_4B was solved from powder X-ray diffraction data: new structure type, space group Pnma, a = 6.0014(1) Aa, b = 5.5041(1) Aa, c = 11.8723(2) Aa, R_I = 0.065, R_P = 0.093. BaPd_4B is isostructural with a = 6.0883(1) Aa, b = 5.6066(1) Aa, c = 12.0050(2) Aa, R_I = 0.062, R_P = 0.097. The relationship of this structure type with the series of derivatives of the CaCu_5 type is discussed. Calculated electronic band structures for palladium, Pd_3B, SrPd_5, SrPd_4B and SrPd_3B are compared. The role of boron and strontium for the electronic properties is discussed in detail. SrPd_4B shows metallic behaviour with a DOS(E_F) ∼ 1.7 eV"-"1.f.u."-"1 at the Fermi level. Magnetic properties, electrical resistivity and specific heat capacity measurements reveal that the two compounds are diamagnetic metallic conductors with low electronic density of states, in agreement, with the electronic structure calculations. (Abstract Copyright , Wiley Periodicals, Inc.)
[en] SrBPO_5: UO_2"2"+ was synthesized using solid state reaction method and characterized using powder X-ray diffraction. PXRD data showed the formation of single phase confirming successful doping of UO_2"2"+. Photo luminescence investigation informed stabilization of Uranium as Uranyl (UO_2"2"+) in SrBPO_5 matrix. Luminescence decay time data suggested two possible environments for UO_2"2"+ with two different life time values
[en] The elastic, phonon and thermodynamic properties of the divalent alkaline-earth hexaboride SrB6 are investigated by using plane-wave pseudopotential density functional theory method. The calculated structure parameters and bulk modulus are well consistent with the available experiment and theoretical data. The pressure dependences of elastic constants Cij, bulk modulus B0, shear modulus G, Young's modulus E and Poisson's ratio σ are also presented. With these elastic parameters, we investigate the mechanical stability and compressibility of SrB6. For the thermodynamic properties, both phonon and quasi-harmonic Debye model methods are adopted. Through the comparison with experimental and other theoretical results, we found the method of quasi-harmonic Debye model is a little better. Moreover, the phonon dispersion relations are also obtained. It is found that there are two LO/TO splitting around 5 THz and 26 THz, respectively.
[en] Highlights: • We found a novel red phosphor to use for white LED. • The main emission peak of the phosphor excited by 466 nm is at 611 nm. • We established the energy level and transition of Eu"3"+ ions in the phosphor. • The phosphor has some helps to improve white LED properties. - Abstract: The Sr_1_._9_3B_2O_5:0.07Eu"3"+ phosphor was synthesized at 1050 °C for 2 h by high-temperature solid state reaction. The crystal structure, luminescent properties and luminescence mechanism were discussed. X-ray powder diffraction (XRD) analysis indicates that the crystal structure of Sr_1_._9_3B_2O_5:0.07Eu"3"+ phosphor is monoclinic Sr_2B_2O_5. Spectra analysis indicate that phosphor demonstrate classic transition of Eu"3"+ ions except matrix absorption, the emission spectrum is composed of six emission peaks at 579 nm, 592 nm, 611 nm, 620 nm, 650 nm and 700 nm and the strongest emitting peak is at 611 nm originated from "5D_0 → "7F_2 electric dipole transition of Eu"3"+ ions, the excitation spectrum shows that phosphor can be excited by UV, near UV and blue light. It is found that Eu"3"+ ions occupy the center of asymmetrical octahedral polyhedron and form C_2 point group. The Stokes frequency shift is 4568 cm"−"1 and the chromaticity coordinate of the Sr_1_._9_3B_2O_5:0.07Eu"3"+ phosphor is x = 0.524, y = 0.316. White LED with the phosphor and YAG:Ce"3"+ phosphor was prepared. The chromaticity coordinate of LED is x = 0.315, y = 0.359, and its irrelative color temperature is 6248 K. The phosphor can be used in white LED
[en] Thermochemical data have been determined for a number of fission product and reactor materials' compounds. Critical assessments have also been made of the available thermochemical data on a number of systems. These data complement the results from similar studies conducted in 1990, and can be used in the appropriate computer codes for calculations of the speciation and transport properties of the fission products during a severe reactor accident. Experimental studies have focussed on the vaporization of tellurium dioxide, caesium ruthenate, strontium and barium borate, indium hydroxide, caesium tellurides, caesium phosphate, caesium hydroxide and caesium iodate and on the thermodynamic properties of the condensed phases CdI2, Cs2CdI4, Cs2Si4O9, Cs2ZrO3, SrB4O7, Ba3B2O6. Critical evaluations have been made of a number of tellurides of importance in severe accident assessments, and analyses have been made of the Fe-Te, Ni-Te and Cr-Te systems. Tables of thermodynamic properties over the temperature range 298.15 K to 3000 K are given. The data should enable the fission product species stabilized in the event of a severe accident and their transport to be predicted with greater confidence. (author). 136 refs.; 18 figs.; 41 tabs