Shozo Oshio

Mechanism of luminance decrease in BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor by oxidation

The mechanism of luminance decrease in blue emitting BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor after annealing has been studied. It was shown experimentally that annealing in air oxidizes BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} and substantially changes the Eu{sup 2+} ion to an Eu{sup 3+} ion. This is also deactivates the Eu{sup 2+} luminescent center, thus decreasing Eu{sup 2+} emission. Furthermore, the compound EuMgAl{sub 11}O{sub 19}, in which the valence of the Eu ion is trivalent, was detected in BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} annealed at temperatures higher than 800 C as a resulting product of oxidation. It was demonstrated that BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} was converted by oxidation into a mixture of the two compounds BaMgAl{sub 10}O{sub 17} and EuMgAl{sub 11}O{sub 19}, and resulting in a further decrease in luminance. This suggests that obstructing the formation of Eu(III)MgAl{sub 11}O{sub 19} during the annealing is essential for alleviating the decrease in luminance. Preparing BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} having both superior crystallinity and completely stoichiometric composition has been found to be effective in alleviating the luminance decrease.

Firing technique for preparing a BaMgAl10O17:Eu2+ phosphor with controlled particle shape and size

The effects of firing temperature on the crystallinity and the luminescent properties of BaMgAl 10 O 17 :Eu 2+ phosphor have been investigated over the temperature range 1000-1800°C under preparative conditions which do not use any flux such as AlF 3 . The effects of particle shape and size of the ingredient Al 2 O 3 on the phosphor have also been studied under a preparative condition which has a firing temperature of 1700°C and does not use any flux. A single-phase BaMgAl 10 O 17 :Eu 2+ with sufficient luminescent properties can be obtained over a firing temperature range of 1600-1800°C through formation of the intermediate product BaAl 2 O 4 :Eu 2+ . Furthermore, the particle shape and size of the ingredient Al 2 O 3 determine the particle shape and size of BaMgAl 10 O 17 :Eu 2+ . High-temperature firing in the absence of any flux has provided for the preparation of a single-phase BaMgAl 10 O 17 :Eu 2+ with various particle shapes, such as spherical or platelike, and particle sizes ranging from 2 to 18 μm.

Mechanism of particle growth of a BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor by firing with AlF{sub 3}

The mechanism of particle growth of the blue emitting BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor by firing with AlF{sub 3} has been clarified. It was found that the reaction between BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} and AlF{sub 3} during firing, on the basis of the following chemical equation, results in recreation of BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} with particle growth BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} + (4/3)AlF{sub 3} {l_reversible} BaMgF{sub 4}:Eu{sup 2+} + (17/3)Al{sub 2}O{sub 3}, the firing of Ba/MgAl{sub 10}O{sub 17}:Eu{sup 2+} with AlF{sub 3} first converts the phosphor into a mixture of the two compounds, BaMgF{sub 4}:Eu{sup 2+} and Al{sub 2}O{sub 3}, at around 1200 C. The BaMgF{sub 4}:Eu{sup 2+} melts at temperatures over 1000 C, then reacts with Al{sub 2}O{sub 3}, and participates in the recreation of both BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} and AlF{sub 3} through a chemical reaction between the two compounds at 1200 C in BaMgF{sub 4}:Eu{sup 2+} solutions. Recreated AlF{sub 3} appears to sublime immediately because it is a material which sublimates with heating. This paper proposes a mechanism for the growth of particle of recreated BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} by the melting of BaMgF{sub 4}:Eu{sup 2+}.

Interaction of reactively sputtered TaOx thin films with In‐Sn‐O thin films and properties of TaOx thin films

The interaction of reactively sputtered TaOx films with In‐Sn‐O (ITO) films was investigated. Phenomena observed in the TaOx/ITO layer structure after a postannealing were studied. These phenomena were: a rise in electrical resistance of the ITO films and a change in color of the layer from transparent to yellowish. Monitoring the gases evolved from the TaOx films during the heating under vacuum showed that incorporation of water into the TaOx films takes place. Evolution of this water from the TaOx films started at around 350 °C, peaked at around 500 °C, and was largely complete at around 650 °C. It was found that the occurrence of the phenomena described above appeared at precisely the temperature at which water was evolved from the TaOx films. It was concluded that the water component incorporated into the TaOx films was the origin of both phenomena. Water present in the conditions under which discharge deposition takes place would be the cause of that incorporation.

Stress and Resistivity of Ta-Mo and Ta-W Sputtered Thin Films

Mo or W doping of sputtered Ta films resulted in the phase transition from tetragonal to cubic and significantly varied stress and resistivity. Prior to complete transition, films consisting of two phases exhibited stress relaxation, and tended to transition to the cubic phase with subsequent annealing. With the complete transition to the cubic phase, films showed an increase in stress. Resistivity was approximately 10–30 µ Ωcm for cubic films, while that for tetragonal films was measured to be 120 µ Ωcm. We determined pure Mo films to be suitable as electrodes due to their lower resistivity, lower stress and better thermal stability in Ta–Mo alloy systems. The proposed Ta–Mo and Ta–W films exhibited the very small stress required for utilization as X-ray absorbers for X-ray photolithographic masks caused by the relaxation due to coexistence of cubic and tetragonal phases.