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[Applied Physics Letters 86 (2005) 211905.pdf](https://mdr.nims.go.jp/filesets/78bbb9f5-528c-4c39-8e77-619180fe88ea/download)

## Creator

[Naoto Hirosaki](https://orcid.org/0000-0001-9218-9557), [Rong-Jun Xie](https://orcid.org/0000-0002-8387-1316), [Koji Kimoto](https://orcid.org/0000-0002-3927-0492), [Takashi Sekiguchi](https://orcid.org/0000-0002-7365-9979), Yoshinobu Yamamoto, [Takayuki Suehiro](https://orcid.org/0000-0001-9444-9738), Mamoru Mitomo

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[Characterization and properties of green-emitting beta-SiAlON : Eu2+ powder phosphors for white light-emitting diodes ](https://mdr.nims.go.jp/datasets/b100c9cd-5914-4cd4-a546-605f90b565a3)

## Fulltext

ViewOnlineExportCitationCrossMarkRESEARCH ARTICLE |  MAY 17 2005Characterization and properties of green-emitting  powder phosphors for white light-emitting diodes Naoto Hirosaki; Rong-Jun Xie; Koji Kimoto; ... et. alAppl. Phys. Lett. 86, 211905 (2005)https://doi.org/10.1063/1.1935027Articles You May Be Interested InEu 2 + -doped Ca - α - SiAlON : A yellow phosphor for white light-emitting diodesAppl. Phys. Lett. (June 2004)Highly efficient white-light-emitting diodes fabricated with short-wavelength yellow oxynitride phosphorsAppl. Phys. Lett. (March 2006)Wavelength-tunable and thermally stable Li - α - sialon : Eu 2 + oxynitride phosphors for white light-emitting diodesAppl. Phys. Lett. (December 2006)β-SiAlON : Eu2+Downloaded from http://pubs.aip.org/aip/apl/article-pdf/doi/10.1063/1.1935027/14639307/211905_1_online.pdfhttps://pubs.aip.org/aip/apl/article/86/21/211905/931445/Characterization-and-properties-of-green-emittinghttps://pubs.aip.org/aip/apl/article/86/21/211905/931445/Characterization-and-properties-of-green-emitting?pdfCoverIconEvent=citehttps://pubs.aip.org/aip/apl/article/86/21/211905/931445/Characterization-and-properties-of-green-emitting?pdfCoverIconEvent=crossmarkjavascript:;javascript:;javascript:;javascript:;https://doi.org/10.1063/1.1935027https://pubs.aip.org/aip/apl/article/84/26/5404/116030/Eu2-doped-Ca-SiAlON-A-yellow-phosphor-for-whitehttps://pubs.aip.org/aip/apl/article/88/10/101104/902694/Highly-efficient-white-light-emitting-diodeshttps://pubs.aip.org/aip/apl/article/89/24/241103/508783/Wavelength-tunable-and-thermally-stable-Li-sialonhttps://servedbyadbutler.com/redirect.spark?MID=176720&plid=2068944&setID=592934&channelID=0&CID=756846&banID=521004218&PID=0&textadID=0&tc=1&adSize=1640x440&matches=%5B%22inurl%3A%5C%2Fapl%22%5D&mt=1682406158514256&spr=1&referrer=http%3A%2F%2Fpubs.aip.org%2Faip%2Fapl%2Farticle-pdf%2Fdoi%2F10.1063%2F1.1935027%2F14639307%2F211905_1_online.pdf&hc=603910e1a6ea4b2897b6afa623a87709eb6d50b2&location=Characterization and properties of green-emitting b-SiAlON:Eu 2+ powderphosphors for white light-emitting diodesNaoto Hirosaki,a! Rong-Jun Xie, and Koji KimotoAdvanced Materials Laboratory, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba,Ibaraki 305-0044, JapanTakashi SekiguchiNano Materials Laboratory, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki305-0044, JapanYoshinobu Yamamoto, Takayuki Suehiro, and Mamoru MitomoAdvanced Materials Laboratory, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba,Ibaraki 305-0044, JapansReceived 20 January 2005; accepted 12 April 2005; published online 17 May 2005dThis letter reports a b-SiAlON:Eu2+ green phosphor with the composition ofEu0.00296Si0.41395Al0.01334O0.0044N0.56528. The phosphor powder exhibits a rod-like morphology withthe length of,4 mm and the diameter of,0.5 mm. It can be excited efficiently over a broadspectral range between 280 and 480 nm, and has an emission peak at 535 nm with a full width athalf maximum of 55 nm. It has a superior color chromaticity ofx=0.32 andy=0.64. The internaland external quantum efficiencies of this phosphor is 70% and 61% atlex=303 nm, respectively.This newly developed green phosphor has potential applications in phosphor-converted whiteLEDs. © 2005 American Institute of Physics. fDOI: 10.1063/1.1935027gWhite light-emitting diodes sLEDsd, the so-callednext-generation solid-state lighting, offer benefits in terms ofreliability, enegy-saving, maintenance and safety, and there-fore are gaining much attention. The availability of whiteLEDs should open up a great number of exciting newapplication fields: white light sources to replace traditionalincandescent and fluorescent lamps, backlights for portableelectronics, medical, and architecture lightings, etc.The first commercially available white LED based on phos-phors was produced in 1996, which is combining ablue light emitting InGaN with a yellowsY1−aGdad3sAl1−bGabdO12:Ce3+sYAG:Ced phosphor.1 How-ever, this type of white light has poor color rendering causedby the color deficiency in the red- and blue-green of thephosphor. The alternative ways to achieve white light areusing an UV LED with RGB sred, green, and bluedphosphors,2–4 or coupling a blue LED to RG phosphors,5 fora high color rendering indexsCRId and a high power output.For this, both of these methods require efficient green phos-phors that should have the excitation wavelength matchingwith the emission wavelength of the UV LEDsslem=350–410 nmd or the blue LEDsslem=450–470 nmd. Cur-rently, the green phosphors used for white LEDs are mostlybased on sulfides, for example, ZnS:Cu, Al,2,3 orSrGa2S4:Eu2+.4 However, the sulfide-based phosphors havelow chemical stabilities, causing the strong temperature de-pendence of chromaticity and degradation of the luminousefficiency of the white LEDs. Therefore, it is necessary todevelop alternative green phosphors with comparable or su-perior performance to the sulfides.Rare-earth doped oxynitride or nitride phosphors havebeen found to have longer excitation and emission wave-lengths compared to their oxidic counterparts.6–9 The lumi-nescence is attributable to the strong nephelauxetic effect andlarge crystal field splitting as the activator ions are coordi-nated to nitrogen. Besides this, the oxynitride or nitride phos-phors are expected to have high thermal and chemical sta-bilities because the crystal structure of the host lattice is builton stiff frameworks consisting of Si–N or Al–N tetrahedra.We have developed a yellow oxynitride phosphor based onEu2+-doped Ca-a-SiAlON, which absorbs strongly over abroad range from UV to visible spectral region.9–11 A warmwhite LED device has been developed by using this yellowphosphor and a blue LED chip.12In this letter, we will report a green oxynitride phosphorwhich is suitable for use in white LEDs: Eu2+-activatedb-SiAlON. The structure ofb-SiAlON is derived fromb-Si3N4 by equivalent substitution of Al–O for Si–N, and itschemical composition can be written as Si6−zAl zOzN8−z szrepresents the number of Al–O pairs substituting for Si–Npairs and 0,zø4.2d.13,14 b-SiAlON has a hexagonal crystalstructure and theP63 space group. In this structure there arecontinuous channels parallel to thec direction. TheEu2+-activatedb-SiAlON phosphor, with the composition ofEu0.00296Si0.41395Al0.01334O0.0044N0.56528, was prepared from94.77 mass % Si3N4, 2.68 mass % AlN, and 2.55 mass %Eu2O3. The powder mixture was then synthesized at 1900 °CadElectronic mail: naoto.hirosaki@nims.go.jp FIG. 1. X-ray diffraction pattern of Eu2+-dopedb-SiAlON.APPLIED PHYSICS LETTERS86, 211905s2005d0003-6951/2005/86~21!/211905/3/$22.50 © 2005 American Institute of Physics86, 211905-1Downloaded from http://pubs.aip.org/aip/apl/article-pdf/doi/10.1063/1.1935027/14639307/211905_1_online.pdfhttp://dx.doi.org/10.1063/1.1935027for 8 h in a 10 atmnitrogen atmosphere. The product phasewas identified by x-ray diffractionsModel RINT2500,Rigaku, Tokyo, Japand using CuKa radiation. The chemicalcomposition of the sample was measured by an inductioncoupled plasma methodsICPd and an oxygen-nitrogen ana-lyzer sTC-436, LECOd. The photoluminescence spectra ofthe powder phosphor were measured by a fluorescence spec-trophotometersModel F-4500, Hitachid at room temperature.The cathodoluminescence study was performed with an elec-tron beam of 5 kV and 200 pA at room temperature.Figure 1 shows the x-ray diffraction pattern of the syn-thesized sample. Obviously, the product is a single phase ofb-Si3N4 or b-SiAlON and free of secondary phases. Thewell-defined sharp diffraction peaks imply that the particleshave high crystallinity. The lattice parameters calculatedfrom the XRD measurement area=7.6090 Å and c=2.9115 Å for this phase. The lattice constants are largerthan those ofb-Si3N4 sa=7.5950 Å andc=2.9023 Åd,15suggesting that the synthesized powder is a solid solution ofb-Si3N4, i.e.,b-SiAlON. Quantitative analysis of the sampleshows the constituent elements in mass percent of 2.16 forEu, 55.6 for Si, 1.64 for Al, 38.0 for N, and 2.1 for O. Thisgives the composition of the synthesized powder ofEu0.0029Si0.40427Al0.0121O0.02679N0.55391. In comparison withthe nominal composition, the measured composition hascomparable Eu, Si, Al, and N contents but possesses ex-tremely high oxygen content. The high oxygen content arisesfrom the inherent surface oxides in the Si3N4 and AlN start-ing powders. Thez value for the measured composition iscalculated as 0.17 using the Si/Al ratio, which is close to0.14 determined from the lattice constants.Figure 2 shows the scanning electron microscopysSEMdimage of theb-SiAlON powder phosphor. The powder con-sists of rod-like crystals which have a uniform size of 4mmin length and 0.5mm in diameter. The fine structure of theb-SiAlON crystal was further analyzed by high-resolutiontransmission electron microscopysHRTEMd as shown in Fig.3sad. The marked interplanard spacings0.3 nmd correspondsto that of thes100d lattice plane ofb-SiAlON. An ultrathinamorphous layer, with the thickness of 0.7 nm, is observedon its surface. Analyzed by TEM-EELSfFig. 3sbdg, Eu atomsare homogeneously distributed both near the edge and at thecenter of theb-SiAlON particles. It suggests that the Euatoms are not segregated on the amorphous surface layer oron the crystals defect sites but coordinated on a specificatomic sitese.g., the channelsd in the b-SiAlON structure.The luminescence properties of the powder phosphor,especially its uniformity, can be characterized by means ofCL.16 A typical CL spectrum of theb-SiAlON phosphor isshown in Fig. 4. A broadband emission centered at 530 nm isobserved. To elucidate the variation of the luminescence in-tensity among different particles, the monochromatic CL im-age was takenswavelength=530 nmd, as shown in the insertin Fig. 3. The particles are seen as rods with uniform bright-FIG. 2. Scanning electron microscopy image of Eu2+-doped b-SiAlONparticles.FIG. 3. sad High-resolution transmission electron microscopysHRTEMd image ofb-SiAlON crystals andsbd the distribution of Eu near the edge and in thecenter ofb-SiAlON.FIG. 4. CathodoluminescencesCLd spectrum of Eu2+-dopedb-SiAlON. Theupper-right inset shows its monochromatic CL image.211905-2 Hirosaki et al. Appl. Phys. Lett. 86, 211905 ~2005!Downloaded from http://pubs.aip.org/aip/apl/article-pdf/doi/10.1063/1.1935027/14639307/211905_1_online.pdfness. Even for each rod-like particle the luminescence inten-sity is also uniform. Moreover, this confirms that the dopedb-SiAlON particle itself gives the green emission.The PL spectra of the powder phosphor are shown inFig. 5. The phosphor exhibits an intense green emission uponUV or visible light excitation. The emission spectrum con-sists of a single broadband with a maximum at 535 nm,which can be ascribed to the allowed 4f →5d transitions ofEu2+. The full width at half maximum of the emission bandis about 55 nm. Upon varying the excitation wavelengththere is no significant changes in the emission spectrum ex-cept the emission intensity. It indicates the presence of onlyone kind of Eu2+ site. Two well-resolved broadbands cen-tered at 303 and 400 nm and a number of shoulders areobserved in the excitation spectrum. The structure in the ex-citation spectrum is due to the crystal field splitting of the 5dlevel of the Eu2+ ions.External sh0d and internal shid quantum efficienciessQEsd were calculated by using the following equations:17h0 =E lPslddlE lEslddlhi =E lPslddlE lfEsld − Rsldgdl,where E(l) /hn, R(l) /hn, and P(l) /hn are the number ofphotons in the spectrum of excitation, reflectance, and emis-sion of the phosphor, respectively. The reflection spectrum ofSpectralon diffusive white standards is used for calibrationsthe reflectivity is nearly 100% in the range of 200–900 nmd.At current synthesis conditions, the internal quantum effi-ciency of theb-SiAlON:Eu2+ phosphor is 70%, 54%, and50% at the excitation wavelength of 303, 405, and 450 nm,respectively, and the corresponding external quantum effi-ciency is 61%, 41%, and 33%.Figure 6 shows the Commission International del’Eclairage sCIEd chromaticity coordinates of theb-SiAlON:Eu2+ phosphor. The chromaticity coordinates ofthe b-SiAlON:Eu2+ phosphor arex=0.32 andy=0.64. It issignificantly better than that of Y3Al5O12:Ce3+, and is supe-rior to ZnS:Cu, Al in color saturation. As seen in the PLspectra, theb-SiAlON:Eu2+ phosphor has strong greenemission under the UVs350–410 nmd or blues450–470 nmdlight excitation. It means theb-SiAlON:Eu2+ phosphorcould be a good green phosphor candidate for creating whitelight in phosphor-converted white LEDs, when combinedwith a UV LED and RB phosphors or with a blue LED anda red phosphor. The development of a white LED deviceusing this green phosphor is under the way, and it will bereported elsewhere.In conclusion, a green oxynitride phosphor, with a nomi-nal composition of Eu0.00296Si0.41395Al0.01334O0.0044N0.56528sb-SiAlON:Eu2+d, has been reported. Its microstructuralcharacterization, PL spectra, quantum efficiencies, and chro-maticity are presented. It is superior to the commerciallyavailable green phosphors YAG:Ce3+ and ZnS:Cu, Al, andhas the internal and external quantum efficiencies of 70%and 61% atlex=303 nm, respectively. Preliminary studieshave shown that this phosphor may find applications in whiteLEDs.1S. Nakamura and G. Fasol,The Blue Laser Diode: GaN Based LightEmitters and LaserssSpringer, Berlin, 1997d.2Y. Sato, N. Takahashi, and S. Sato, Jpn. 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Omichi, N. Kimura, M. Ohashi, D. Tanaka, N. Hirosaki, Y.Yamamoto, R.-J. Xie, and T. Suehiro, Opt. Lett.29, 2001s2004d.13Y. Oyama and O. Kamigaito, Jpn. J. Appl. Phys.10, 1637s1971d.14K. H. Jack and W. I. Wilson, NaturesLondond, Phys. Sci.238, 28 s1972d.15R. Grun, Acta Crystallogr.B35, 800 s1979d.16T. Sekiguchi, Mater. Res. Soc. Symp. Proc.588, 75 s2000d.17K. Ohkubo and T. Shigeta, J. Illum. Engng. Inst. Jpn. 83, 87s1999d.FIG. 5. Photoluminescence spectra of Eu2+-doped b-SiAlON slem=535 nm for excitation andlex=303, 405, and 450 nm for emissiond.FIG. 6. Chromaticity coordinates of Eu2+-dopedb-SiAlON phosphors.211905-3 Hirosaki et al. Appl. Phys. Lett. 86, 211905 ~2005!Downloaded from http://pubs.aip.org/aip/apl/article-pdf/doi/10.1063/1.1935027/14639307/211905_1_online.pdf