OKAMOTO Shinji Tottori University, Dept. of Engineering, Research Associate, 工学部, リサーチアソシエーツ
MITA Yoh Tokyo University of Technology, Faculty of Engineering, Professor, 工学部, 教授 (20200040)
|Budget Amount *help
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1998: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1997: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1996: ¥700,000 (Direct Cost: ¥700,000)
Field emission displays (FED) are new thin, flat displays, which can reproduce moving pictures with fast response. This work has explored phosphors, which can meet the requirements of low-voltage, high-density electron excitation ; I.e. sufficient electrical conductivity and ruggedness as well as high efficiency.
(1) Oxides containing elements with mixed valency.
It was found that partial substitution of Al with either Ga or In in green-emitting YィイD23ィエD2AlィイD25ィエD2OィイD212ィエD2 : Tb decreases electrical resistivity of the phosphor, resulting in suppression of electrical charging of the phosphor surface. Presumably mixed valency of such elements as Ga, In or Ti increases the oxygen vacancy concentration, leading to a decrease in the resistivity.
(2) Mechanism of efficiency improvement by addition of a IIIb-group element.
Addition of a IIIb-group element, e.g. Al, to a red-emitting phosphor SrTiOィイD23ィエD2 : Pr increases the luminescence efficiency by more than 200 times. This work has elucid
ated two types of mechanism operating for this effect ; (a) charge compensation between PrィイD13ィエD1+ at SrィイD12ィエD1+ sites and AlィイD13ィエD1+ at TiィイD14ィエD1+ sites and (b) elimination of planar faults in SrTiOィイD23ィエD2, crystals (thin SrO layers) by formation of Sr-aluminates.
An efficiency can be improved also in other compounds with planar faults, e.g. Ruddlesden-Popper phases. Similar Al-addition effect observed in SrInィイD22ィエD2OィイD24ィエD2 : PrィイD13ィエD1+ has been investigated based on the above consideration.
(3) Feasibility of a conventional blue phosphor, ZnS : Ag, Al, as an FED phosphor
A commercial CRT phosphor ZnS : Ag, Al has a high efficiency, but it shows considerable luminance saturation under high-density excitation. This work investigated traps, which possibly induce Auger process, the main nonradiative process. Optical measurements show that deep impurity levels by Ag and Al are responsible to the Auger process. The luminance saturation is, therefore, caused by the factor inherent to the material composition. Less