Luminescence properties and formation process of ͑Sr 1−u Ba u ͒Si 2 O 2 N 2 :Eu 2+ , phosphors suitable for white light-emmitting ͑LEDs͒, were investigated. These phosphors were synthesized by a method using ͑Sr 1−u Ba u ͒ 2 SiO 4 :Eu 2+ as a precursor instead of simple oxides. Compared with a conventional solid-state reaction method, this method provides increased luminescence efficiency. X-ray diffraction analysis has indicated that transformation of low-temperature type ͑Sr 1−u Ba u ͒Si 2 O 2 N 2 :Eu 2+ to high-temperature type, which has a higher luminescence efficiency, occurs with a higher probability when ͑Sr 1−u Ba u ͒ 2 SiO 4 :Eu 2+ is used as a precursor. Under 460 nm excitation, ͑Sr 1−u Ba u ͒Si 2 O 2 N 2 :Eu 2+ shows an emission band peaked at 550-590 nm for varied Ba fraction u. This series of materials shows the high integrated photoluminescence intensity at u = 0.25-0.75. Particularly, at u = 0.5, it shows the highest quantum output, which is about 1.2 times as high as that of the commercial yellow phosphor, ͑Y,Gd͒ 3 Al 5 O 12 :Ce 3+ , P46-Y3. The internal quantum efficiency is estimated to be about 80% for samples of u = 0.5 and 0.75. The high efficiency and small thermal quenching allow these materials to be applied to white LEDs.

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BaSi 2 O 2 N 2 :Eu 2+ ͑Ba 1−x Eu x Si 2 O 2 N 2 ͒ phosphor was prepared by a method using Ba 2 SiO 4 :Eu 2+ as a precursor with a starting composition of ͑Ba 1−x Eu x ͒ 2 Si 1−u O 4−2u :Si 3 N 4 = 1/2:͑3 + u͒v/6 ͑x = 0-0.1, u = 0-0.05, v = 1-1.05͒. The formation behavior of BaSi 2 O 2 N 2 :Eu 2+ and secondary phases was investigated in detail by means of X-ray diffraction analysis of the samples prepared under various conditions. The formation of secondary phases was suppressed by the method employed in this work and a single phase of BaSi 2 O 2 N 2 :Eu 2+ was successfully obtained when the starting compositions with x = 0-0.7, u = 0.05, and v = 1.05 were used. BaSi 2 O 2 N 2 :Eu 2+ phosphors showed the bluish-green emission peaking at 490-500 nm along with varying concentrations of Eu 2+ from 1 to 10 mol % ͑x = 0-0.1͒; particularly, the BaSi 2 O 2 N 2 :Eu 2+ ͑5 mol %, x = 0.05͒ phosphor showed an exceedingly strong emission peak intensity, which was about 3.7 times higher than that of the commercial yellow phosphor, ͑Y,Gd͒ 3 Al 5 O 12 :Ce 3+ ͑P46-Y3͒, under 460 nm excitation light. Furthermore, this phosphor maintained luminescence intensity at 150°C by 75% of the value measured at room temperature. These excellent luminescence properties and small thermal quenching suggested this phosphor to be applied as a bluish-green component for phosphor conversion white light-emitting diodes.The applications of white light-emitting diodes ͑LEDs͒ to solidstate lighting source for general illumination have been continuously expanded owing to their promising features such as lower energy consumption, long lifetime, mercury-free, and so on. 1,2 The common white LEDs are fabricated by the conversion of green-yellow-red phosphors on a blue LED, which is called phosphor conversion ͑pc͒-LED. 3-5 This type needs efficient phosphors that can be excited by a blue light. In recent years, many efficient phosphors have been developed and used in practical applications. [6][7][8][9][10][11][12][13] MSi 2 O 2 N 2 :Eu 2+ ͑M = Ca,Sr,Ba͒ compounds have recently attracted much attention as conversion phosphors for white LEDs due to their remarkable luminescence properties and thermal stabilities. 6-8,10,14-18 The emission band of MSi 2 O 2 N 2 :Eu 2+ ͑M = Ca,Sr,Ba͒ phosphors can be tuned between ϳ490 and 585 nm depending on M ion types ͑single or multicomponent systems͒ and Eu 2+ concentrations under 460 nm blue light excitation, which can make it possible to realize white LEDs with improved high color rendering index ͑CRI͒. 6-8,10,14-18 Among MSi 2 O 2 N 2 :Eu 2+ phosphors, BaSi 2 O 2 N 2 :Eu 2+ shows the narrow emission band peaking at 490-500 nm, reflecting the crystal structure of the host material, BaSi 2 O 2 N 2 , in which there is only one Ba site with highly symmetric environment. 6,19 This emission band is suitable to compensate for the lack of the bluish-green region in the spectrum of white LEDs consisting of a blue LED chip and green-yellow-red phosphors. Practically, Kimura et al. 4 and Xie et al. 5 fabricated white LEDs with ul...

This work has investigated luminescence properties of SrSi 2 O 2 N 2 : Eu 2 phosphors synthesized by a new method using Sr 2 SiO 4 : Eu 2 as a precursor. Compared with a conventional solid-state reaction method, this method provides increased crystallinity and luminescence efficiency. X-ray diffraction analysis has indicated that SrSi 2 O 2 N 2 : Eu 2 formed as an almost single-phase, but chemical analysis has shown that obtained samples have an oxygen nitrogen atomic ratio deviated from the stoichiometric composition. It can be expected that luminescence efficiency of this phosphor will be higher for the stoichiometric composition than for non-stoichiometric ones. Under 460 nm excitation, this phosphor shows an emission band peaked at 538-564 nm for varied Eu 2 concentration, and shows the maximum at 15 mol! with high integrated photoluminescence intensity, which is about 1.05 times as high as that of the commercial yellow phosphor, Y,Gd 3 Al 5 O 12 : Ce 3 P46-Y3 .

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