Shun-ichi Kubota

Luminescence of Eu3+, Tb3+ and Tm3+ in SrLaGa3O7

The luminescence properties of Eu3+, Tb3+ and Tm3+ in strontium–lanthanum gallate, SrLaGa3O7, solid solutions were systematically examined. The emission intensity of Eu3+, Tb3+ have maxima at x=0.8 of SrLa1−xRxGa3O7 (R=Eu3+, Tb3+) under UV excitation and the activator concentration dependencies of the emission intensity are unique. The mechanism of concentration dependence is discussed by the crystal structure and the energy migration.

Sr3Al10SiO20:Eu2+ as a blue luminescent material for plasma displays

A new luminescent material, Sr3Al10SiO20:Eu2+, has been synthesized. The material exhibits an emission peak at 466 nm for the (Sr0.993Eu0.007)3Al10SiO20 and a CIE chromaticity of (x=0.145, y=0.124), with relative intensity of 60% of commercial phosphor BaMgAl10O17:Eu2+ under vaccum ultraviolet excitation.

Power factors of Ca3Co2O6 and Ca3Co2O6-based solid solutions

Abstract A polycrystalline sample of Ca3Co2O6 was prepared by solid state reaction of CaCO3 and Co3O4 at 1243 K in air. The electrical resistivity (ρ) of Ca3Co2O6 exhibited semiconducting behavior and ranged from 1.6×102 to 1.3×10−1 Ω cm with temperature from 400 to 1170 K. The Seebeck coefficient (S) showed positive value, and decreased from 660 to 140 μV/K with increasing the temperature from 350 to 1170 K. The power factor (S2/ρ) tended to increase with increasing temperature, and the maximum value was 1.6×10−5 W/(m K2) at 1150 K. Samples with the starting compositions of (Ca1−xAx)3Co2O6 (A=Y, La, and Bi, x=0.03) and Ca3(Co1−yMy)2O6 (M=Cr and Cu, y=0.03) were also heated at 1243 K in air to prepare Ca3Co2O6-based solid solutions. The changes of lattice parameters and widths of X-ray diffraction peaks for the obtained samples indicated substitutions of Y, La, Bi for Ca, Cr and Cu for Co, although the samples included trace amount of impurities. Substitutions of Bi and Cu increased the power factors of the solid solutions, and the maximum values were 3.4×10−5 W/(m K2) (A=Bi at 1130 K) and 2.3×10−5 W/(m K2) (M=Cu at 1150 K). The Seebeck coefficients of the solid solutions with Y and La were negative below 400 K.

Luminescent Property of Eu3 + in a New Compound, ( Sr0.99La1.01 ) Zn0.99 O 3.495

The luminescent property of Eu 3+ in (Sr 0.99 La 1.01 )Zn 0.99 O 3.495 solid solution was systematically examined. (Sr 0.99 La 1.01 )Zn 0.99 O 3.495 was newly found in the Sr-La-Zn-O system. Under ultraviolet excitation, emission intensity increases with increasing Eu 3+ concentration to y = 0.7 in (Sr 0.99 La 1.0μ1-x Eu y )Zn 0.99 O (3.495-0.015y ) solid solution. The crystal system of the solid solution changed from tetragonal (y = 0.1 - 0.4) to orthorhombic (y = 0.5 ∼ 0.7).

Luminescent Properties of Eu3 + in Defect Apatite, Sr3La6 ( SiO4 ) 6

Sr 3 La 6 (SiO 4 ) 6 is one of the defect silicate apatites. Eu 3+ -doped Sr 3 La 6 (SiO 4 ) 6 , i.e., Sr 3 (La 1-x Eu x ) 6 (SiO 4 ) 6 solid solutions, were synthesized and their luminescent properties were studied. The emission intensity increased with increasing Eu 3+ concentration up to x = 0.2 and decreased to x = 0.8. At x = 0.9, it raised again dramatically. In addition, the lattice parameter, a, decreased quickly with increasing Eu 3+ concentration between x = 0.8 and x = 1.0. This fact was explained by the change of site occu-pancies of Eu 3+ , La 3+ , and Sr 2+ ions and defects on the 4f and 6h sites in Sr 3 (La 1-x Eu x ) 6 (SiO 4 ) 6 .

Energy migration in EuTa7O19, TbTa7O19 and La0.86 Tm0.14 Ta7O19

The energy migration processes in EuTa2O19, TbTa7O14 and La0.86 Tm0.14 Ta7O19, are reported. The decay characteristics of the Eu1. and Tb1 emission can be explained by using a quasi-two-dimensional migration model, not by a two-dimensional migration model. In contrast, the characteristics of the Tm3 emission can be explained by using the cross-relaxation energy transfer model.

Luminescence of Eu3+ in La1-xEuxTa7O19 (0≤x≤1) solid solution

Abstract The luminescence properties of Eu 3+ in La 1− x Eu x Ta 7 O 19 solid solution were examined systematically. In the structure the nearest neighbours of La 3+ sites doped with Eu 3+ ions are arranged two-dimensionally with proper separations of about 0.62 nm. An intense emission peak is observed at 610 nm together with supplementary weak peaks. All the peaks can be ascribed to 5 D j → 7 F j′ (j = 0,1; j′=0,1,2,3,4) transitions of Eu 3+ . The emission of the 5 D 0 → 7 F 2 transition becomes intense and saturates with the Eu 3+ concentration. As a result, the profile of the concentration quenching implies that energy migration of excited Eu 3+ hardly takes place in La 1− x Eu x Ta 7 O 19 solid solution.

Gd3GaO6 by X-ray powder diffraction

The structure of trigadolinium gallate, Gd 3 GaO 6 , was solved ab initio from conventional X-ray powder diffraction data. Gd 3 GaO 6 has a non-centrosymmetric orthorhombic structure (Cmc2 1 ). The structure was refined by the Rietveld method, showing that the Gd atoms are in two different sites of sevenfold coordination and that the Ga atoms are in distorted oxygen tetrahedra. Gd 3 GaO 6 was found to be isotypic with Er 3 GaS 6 .

Luminescence properties of rare earth ions in polytantalate

The luminescence properties of R 3+ (R 3+ =Eu 3+ , Tb 3+ , Tm 3+ ) in La 1-x R x Ta 7 O 19 solid solution were systematically examined. In this host lattice, the distance between nearest neighbors of the La 3+ site which were substituted by the R 3+ ions, were very long (about 0.62 nm) and the sites locate two-dimensionally. The critical concentration at which the concentration quenching occurred under UV excitation were x=1.0 in La 1-x Eu x Ta 7 O 19 , x=0.9 in La 1-x Tb x Ta 7 O 19 and x=0.14 in La 1-x Tm x Ta 7 O 19 . Furthermore the energy migration process of these samples were investigated.

Luminescence properties of Gd1−xBixTa7O19 (0<x≤1)

Abstract The luminescence properties of Bi 3+ in GdTa 7 O 19 solid solution were systematically examined. The samples were synthesized by a solid state reaction. The properties studied in this work were the excitation, luminescence, and diffuse reflection spectra. Upon UV excitation, the maximum of emission band of Bi 3+ shifted from 480 to 505nm for Gd 1− x Bi x Ta 7 O 19 . The excitation and emission spectra of Bi 3+ emission in Gd 1− x Bi x Ta 7 O 19 (0 x ≤1) consist of broad band.