In order to develop a yellow phosphor that emits efficiently under the 450–470 nm excitation range, we have synthesized a Eu2+-activated Sr3SiO5 yellow phosphor and attempted to develop white light-emitting diodes (LEDs) by combining them with a InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Sr3SiO5:Eu phosphor are clearly observed at 460 nm and at 570 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that InGaN (460 nm chip)-based Sr3SiO5:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce.

We have synthesized a Eu2+-activated Sr2SiO4 yellow phosphor and investigated an attempt to develop white light-emitting diodes (LEDs) by combining it with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr2SiO4:Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that GaN (400-nm chip)-based Sr2SiO4:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460-nm chip)-based YAG:Ce.

On the basis of the possibility that there might exist a mixed composition of the Y(As,Nb,P,V)O4 system of better luminescent performance than the single-compound phosphors at the VUV excitation, a solution combinatorial chemistry synthesis and characterization was employed in the present investigation. Quaternary and ternary combinatorial libraries were designed to implement an efficient screening process. In parallel, the first-principle calculations were also carried out on the basis of the density functional theory to give a reasonable interpretation to the results from the combinatorial chemistry screening process. It was found that a new phosphor, Y0.9(P0.92V0.03Nb0.05)O4:Eu3+, which was obtained through the three-step combinatorial screening, shows promising luminance and CIE color chromaticity that could be comparable to the commercially available red phosphor used for the PDP application. As a result of the luminescent mechanism study in association with the calculated density of states (DOS), the entire energy transfer route under the 147-nm excitation was revealed for the newly found phosphor, Y0.9(P0.92V0.03Nb0.05)O4:Eu3+.

BaMgAl 10 O 17 : Eu 2+ (BAM) phosphors used for plasma display panels (PDP) are compelled to be exposed to an oxidizing environment at about 500 °C, which is currently unavoidable in the actual manufacturing process of PDP. We investigated the mechanism of the luminance degradation of BAM caused by the annealing at 500 °C, using photoluminescence (PL), decay measurement, and synchrotron light source x-ray absorption and diffraction measurements. The annealing treatment altered the valence state of Eu ions, whereas no new Eu compounds were detected. By estimating the exact fraction of divalent Eu ions and by comparing it with the luminance data, we found that more than 30% degradation of luminance was induced at the expense of only a few percent of divalent Eu. This finding led us to suggest that the origin of the dramatic decrease in PL intensity is not due to the valence state change but due to the local structure change surrounding the Eu2+ ions.

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Y2O3:Eu phosphor particles were prepared by flame spray pyrolysis and compared with the particles prepared by general spray pyrolysis. The particles prepared by flame spray pyrolysis had a spherical and dense morphology and were finer than the particles prepared by general spray pyrolysis. Flame temperature was an important factor in the preparation of the phosphor particles by flame spray pyrolysis. To obtain Y2O3:Eu particles with a uniformly dense structure, a sufficiently high temperature to form monoclinic phase was required. Too low flame temperature generated nonspherical and hollow particles with cubic phase because the particles did not melt completely, and too high flame temperature of flame generated many nanoparticles due to evaporation. After stepwise post-treatment of as-prepared particles with monoclinic phase and the dense structure, Y2O3:Eu phosphor particles with high brightness and cubic phase were obtained. The Y2O3:Eu phosphor particles prepared by flame spray pyrolysis showed 120% photoluminescence intensity in comparison with the particles prepared by general spray pyrolysis.

Oxidation studies were conducted on AI2O3-SiC and mullite-Sic composites at 1375" to 1575°C in O2 and in Ar-l% 02. The composites were prepared by hot-pressing mixtures of A1203 or mullite and SIC powders. The reaction products contained alumina, mullite, an aluminosilicate liquid, and gas bubbles. The parabolic rate constants were about 3 orders of magnitude higher than those expected for the oxidation of Sic. Higher rates are caused by higher oxygen permeabilities through the reaction products than through pure silica. Our results suggest that oxygen permeabilities are comparable in the three condensed phases observed in the reaction products. [Key words: composites, silicon carbide, oxidation, mullite, alumina.] used were 1-to 4-pm Sic particles,' 0.3-pm alumina,' and <6-pm mullite.g Powder mixtures of desired composition were homogenized, in batches of -0.1 kg, by ball-milling for 18 h using alumina balls and 2-propanol as a dispersing agent. The ball-milled powders were dried at room temperature, and subsequently pressed into pellets 31.6 mm in diameter. The pellets were hot-pressed at 1650°C for 10 min using a pressure of 25 MPa. The hot-pressed samples attained a density of at least 99% of theoretical value. Silicon carbide particles were well dispersed in the matrix in the hot-pressed samples, as shown in the microstructures in Fig. 1.Hot-pressed samples were cut into coupons 14 mm X 10 mm x 1 mm in size. A 1-mm-diameter hole was drilled

The photoluminescence behavior of (Y 1Ϫx Tb x )PO 4 phosphor was investigated by measuring emission and excitation spectra, and decay curves. The relative emission intensity and the decay time have been monitored as a function of Tb 3ϩ concentration for both 5 D 4 Ϫ 7 F j and 5 D 3 Ϫ 7 F j transitions. The decay behavior of 5 D 3 -7 F j transition, for which well known cross-relaxation has been accepted as a main factor, was analyzed by direct quenching mechanism on the basis of dipole-dipole interaction. It is, however, impossible to characterize the 5 D 4 Ϫ 7 F j transition using the direct quenching scheme. In fact, the decay curves of 5 D 4 Ϫ 7 F j transition could be analyzed by intercenter energy migration. Another type of cross-relaxation was suggested to explain the quenching of 5 D 4 Ϫ 7 F j transition.