ARTICLE IN PRESS 2 times higher than that of incandescent lamps.The superior suitability for use in white LED and can be used in -rendering index white multichromatic LEDs with excellent wid of white的，hg CCT,and brilliant color-rendering properties. LEDs haor general nation,mu Acknowledgments g-sialon:Eu The studies described in this review were partially white LED s-in-Aid fo the Er th efcacy/W:Later.Kimura t added a bluish-green BaSi2O2N2:Eu2+phosphor into the above phosphor mixture and ta xis et al.72 used siaon Yh References phosphors as well as a blue LED to fabricate white LEDs. The CRI and luminous wer K.K Ra= 3 an 73 or hend of and LEDs s using ark.Chot.Yoon.SJ.L.C.H.Kim. uminous efficacy Ra=92 In addition.oxynitride/nitride phosphors were used in H4 combination with NUV LED chips to generate white light y e() 199)170 by Tak shi et al.[w A using nuv ieD .C. chip with a peak emission wavelength of 405nm.The s o) [2]N.Hire R.-J.Xie.K.Sakuma.Ovo Buturi 74 (2005)1449 76( 6.Summary Ya and lu Laurent.Guyader,P.L'Haridon,P.Verdier pro phors recently developed foruse in white LEDswere uP.Morys.W.Schnick.A.Scilmcier.J.Phys. s0ds61(200,200 d excite stat or the electrons of rare w to large crystal-field splitting and a strong dal.H.T.Hintzen efTect as a result of a high degree of crosslinking SiN s an o K. 55202129 M Wang.M.Mitome.Lumin. irradiation.and then be applied 679 The emission colo of depends greaty the rdination,covalence,bond length.site sizeand field strength in which they reside,making it possible to 1 adjust/tune the emission wavelength over a wide range by per,W.Milius,W.Schnick..Anorg Allg.Chem.621 phosph ha ated it er.W.Schnick.Anorg Allg.Chem.621(199)1037. Please cite this articles:RJ.Xie,N.Hirosaki,Sci.Technol.Adv.Mater.(do:.0 2 times higher than that of incandescent lamps. The color-rendering index (CRI) of the bichromatic white LEDs using a-sialon:Eu2+ was Ra=55–72, which is acceptable for some applications such as backlights, flashlights, and car interior lighting. To improve the color-rendering properties of white LEDs for general illumination, multichromatic white LEDs have been prepared using phosphor blends. Sakuma et al. [70] fabricated white LEDs by combining b-sialon:Eu2+, a-sialon:Eu2+, and CaAlSiN3:Eu2+ with a blue-LED chip. The CRI value of the white LED (CCT ¼ 2840 K) was Ra ¼ 81–88, and the luminous efficacy was 24–28 lm/W. Later, Kimura et al. [71] added a bluish-green BaSi2O2N2:Eu2+ phosphor into the above phosphor mixture and obtained ultrahigh color rendering and high-efficiency white LEDs (Ra ¼ 95–98, 28–35 lm/W). Xie et al. [72] used a-sialon:Yb2+ and Sr2Si5N8:Eu2+ phosphors as well as a blue LED to fabricate white LEDs. The CRI and luminous efficacy of these LEDs were Ra ¼ 82–83 and 17–23 lm/W, respectively. Mueller-Mach et al. [73] reported highly efficient white LEDs with Ra90, using the phosphor blend of Sr2Si5N8:Eu2+ and SrSi2O2 N2:Eu2+. Recently, Yang et al. [74] have reported white LEDs using SrSi2O2N2:Eu2+ and CaSiN2:Ce3+, which showed a luminous efficacy of 30 lm/W and a CRI of Ra ¼ 92. In addition, oxynitride/nitride phosphors were used in combination with NUV LED chips to generate white light by Takahashi et al. [75]. White LEDs were prepared by pumping the phosphor blend of JEM:Ce3+, b-sialon:Eu2+, Ca-a-sialon:Eu2+, and CaAlSiN3:Eu2+ using NUV LED chip with a peak emission wavelength of 405 nm. The CRI and luminous efficacy of these white LEDs with CCTs of 2830–4350 K were Ra ¼ 95–96 and 19–20 lm/W, respectively. 6. Summary In this review, the crystal structures and luminescent properties of silicon-based oxynitride and nitride phos￾phors recently developed for use in white LEDs were described. The excited state of the 5d electrons of rare￾earth elements is significantly lowered to low energies due to large crystal-field splitting and a strong nephelauxetic effect as a result of a high degree of crosslinking SiN4 tetrahedra in the structure of silicon-based oxynitrides and nitrides. This enables silicon-based oxynitride and nitride phosphors to be excited efficiently by UV or blue-light irradiation, and then be applied as downconversion luminescent materials in white LEDs. The emission color of rare-earth ions (i.e., Eu2+, Ce3+, Yb2+) depends greatly on the surrounding environments including symmetry, coordination, covalence, bond length, site size, and crystal- field strength in which they reside, making it possible to adjust/tune the emission wavelength over a wide range by varying the compositional design. The novel class of oxynitride and nitride phosphors has demonstrated its superior suitability for use in white LED and can be used in bichromatic or multichromatic LEDs with excellent properties of high luminous efficacy, high chromatic stability, a wide range of white light with adjustable CCT, and brilliant color-rendering properties. Acknowledgments The studies described in this review were partially supported by Grants-in-Aid for the Encouragement of Young Scientists (B) Contract No. 17760550, from the Japan Society for the Promotion of Science (JSPS). References [1] S. Nakamura, G. 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