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Fine particles of red emission phosphors, (Y 1Ϫx La x ) 2 O 3 :Eu 3ϩ , have been synthesized by microwave-assisted hydrolysis using urea, and their luminescent properties were compared with Y 2 O 3 :Eu 3ϩ fine particles without La 3ϩ doping as well as a commercial Y 2 O 3 :Eu 3ϩ . The limiting value of Eu 3ϩ content where concentration quenching starts was enhanced by La 3ϩ doping into the host Y 2 O 3 lattice, and photoluminescence emission intensity of the La 3ϩ -doped samples rose more than before doping. On the contrary to the general tendency that emission intensity decreases with particle size reduction, the emission intensity of the (Y 1Ϫx La x ) 2 O 3 :Eu 3ϩ fine particles ͑0.57 m͒ was equal to that of the larger commercial Y 2 O 3 :Eu 3ϩ ͑3.1 m͒.High efficiency phosphor materials with crystalline monodispersive fine particles have been requested to apply for high resolution and high efficiency planar displays. In these applications, small phosphor particles of less than 5 m in diameter are required and the crystallinity of the phosphor particles is an important factor. However, the luminescence intensity decreases when the particle size is less than 3 m wide, because of an increase in surface defects that induce quench luminescence. 1 Therefore, synthesis of small phosphor particles with high luminescent efficiency is a key process to realizing higher resolution, lower loading, and higher density in display devices.Yttrium oxide doped with Eu 3ϩ (Y 2 O 3 :Eu 3ϩ ) is one redemitting phosphor commonly used in tricolor fluorescent lamp and field-emission display because this material has efficient luminescence under ultraviolet and electron-beam excitation. 2 Although a conventional ceramic method is usually employed to obtain phosphor materials, this route needs a grinding or milling process to obtain fine particles, which produces some defects in the phosphor crystal surface. To achieve small phosphor particles of high quality, various preparation routes via both dry and wet chemical processes have been proposed. 3-14 However, photoluminescence of the Y 2 O 3 :Eu 3ϩ usually decreases as the particles become smaller, 13,14 and, therefore, there are few reports on luminescent fine particles that have sufficient emission intensities comparable to commercial bulk phosphors. 8 Generally, emission intensity is usually increased with the concentration of the Eu 3ϩ activator. However, when the concentration of the activator exceeds a certain level, the luminescence intensity is quenched because of pairing or aggregation of activator ions at high concentration, which induces the migration of excitation by resonant energy transfer between the Eu 3ϩ ions to carry the energy to a quenching center existing at the surface of the crystal. 15 In this communication, therefore, the Y 2 O 3 host lattice was expanded by doping the larger La 3ϩ into the Y 3ϩ site, resulting in lengthening the distance of Eu 3ϩ activators. 16 As a result, the transfer of excitation energy between Eu 3ϩ ions was suppressed up to higher europium...

Fine Sr2CeO4 particles of a blue emission phosphor have been synthesized using a chemical co-precipitation technique, and the textual and optical properties were compared with the one synthesized by the conventional solid-state reaction method. Mean particle size of the prepared Sr2CeO4 fine particles was smaller than that given by the sample prepared from the solid-state reaction method. However, photoluminescence intensity was maintained in spite that it usually decreases with the particle size reduction.

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