ARTICLE IN PRESS Al-O for Si-N,and its chemical composition can be optimal Eu?+concentration was about 0.3mol%.In wntten as Si airs re and the po. 2- on inten 33 P63/m space group 51,52).In this structure there are Xie et al.34]reported the green emission of Ybin Ca- continuous cha asialon.As can be seen in Fig.9.the excitation spectrum ak phosphor ows a broa leng 5nm.and bl e ih Fig.8.The broad emission spectrum has a full-width at excitation. from the half-maximum of 55nm.Two well-resolved broad bands transition usually occurs between 360 and centered at 303 anc I 400nm are observed in the 450 nm,as has b en sho iotiaidesnuondes.suphaea nl (400-420nm)or blue (420-470nm)light excitation.Xie ascribed to the large crystal-field splitting and the strong value and the n a The lt at~620nm by Bachmann et al.[56]. had higher phase purity,a smaller and more uniform MSiO2N2 compounds crystallize in a monoclinic lattice particle size.and produced greater emission:(ii)the th 一CaoN a SrSizON are structurally related,both representing a new with tha Si atom while the h atom There are four tpes of site for the M?ions.each sur ounded by six and vellowish emission with a maximum intensity at 562nm,SrSi2O2N:Eu? emits Thes e results were shows a flat 200 300 500 700 300 400 500 600 70 Wavelength(nm) Wavelength (nm) Please cite this articles:RJ.Xie,N.Hirosaki,Sci.Technol.Adv.Mater.(do:.0 Al–O for Si–N, and its chemical composition can be written as Si6zAlzOzN8z (z represents the number of Al–O pairs substituting for Si–N pairs, and 0ozp4.2). b-Sialon has a hexagonal crystal structure and the P63 or P63/m space group [51,52]. In this structure there are continuous channels parallel to the c direction (see Fig. 7). The b-sialon:Eu2+ phosphor produces intense green emission with a peak located at 538 nm, as can be seen in Fig. 8. The broad emission spectrum has a full-width at half-maximum of 55 nm. Two well-resolved broad bands centered at 303 and 400 nm are observed in the excitation spectrum. The broad excitation range enables the b-sialon:Eu2+ phosphor to emit strongly under NUV (400–420 nm) or blue (420–470 nm) light excitation. Xie et al. [33] investigated the effects of the z-value and the Eu2+ concentration on the phase formation and lumines￾cent properties of b-sialon:Eu2+ phosphors. The results showed that (i) the samples with lower z-values (zo1.0) had higher phase purity, a smaller and more uniform particle size, and produced greater emission; (ii) the optimal Eu2+ concentration was about 0.3 mol%. In addition, the b-sialon:Eu2+ phosphor showed low thermal quenching; its emission intensity at 150 1C was 86% of that measured at room temperature [33]. Xie et al. [34] reported the green emission of Yb2+ in Ca￾a-sialon. As can be seen in Fig. 9, the excitation spectrum shows a broad band centered at 445 nm, and the peak emission wavelength is about 550 nm upon blue-light excitation. The emission of Yb2+, arising from the transition 4f135d-4f14, usually occurs between 360 and 450 nm, as has been shown for halides, fluorides, sulphates, and phosphates [53–55]. However, luminescence occurs at low energies in Ca-a-sialon, which can principally be ascribed to the large crystal-field splitting and the strong nephelauxetic effect induced as a result of the nitrogen-rich coordination of Yb2+ in a-sialon. A much longer wavelength emission of Yb2+ in SrSi2O2N2 was observed at 620 nm by Bachmann et al. [56]. MSi2O2N2 compounds crystallize in a monoclinic lattice with different space groups and lattice parameters for M ¼ Ca, Sr, and Ba: CaSi2O2N2 (P21/c), SrSi2O2N2 (P21/m), and BaSi2O2N2 (P2/m) [25,35]. CaSi2O2N2 and SrSi2O2N2 are structurally related, both representing a new class of layered materials with layers of (Si2O2N2) 2 that consist of SiON3 tetrahedrons. The N atom bridges three Si atoms, while the O atom is bound terminally to the Si atom. There are four types of site for the M2+ ions, each surrounded by six oxygen atoms in the form of a distorted trigonal prism. The excitation and emission spectra of Eu2+-doped MSi2O2N2 materials are given in Fig. 10. As can be seen, CaSi2O2N2:Eu2+ shows a yellowish emission with a maximum intensity at 562 nm, SrSi2O2N:Eu2+ emits a green color with a maximum intensity at 543 nm, and BaSi2O2N2:Eu2+ yields blue–green emission with a peak at 491 nm. These results were also observed by Li et al. [35]. The excitation spectrum of CaSi2O2N2:Eu2+ shows a flat and broad band extending from 300 to 450 nm, while there are two well-resolved broad bands centered at 300 and ARTICLE IN PRESS Fig. 8. Excitation and emission spectra of b-sialon:Eu2+ with the composition of Si5.5Al0.5O0.5N7.5:Eu0.03. Fig. 9. Excitation and emission spectra of a-sialon:Yb2+ with the composition of Ca0.995Yb0.005Si9Al3ON15. Fig. 7. Crystal structure of b-sialon viewed along the [0 0 1] direction. The red and green spheres represent Si/Al and O/N atoms, respectively. 6 R.-J. Xie, N. Hirosaki / Science and Technology of Advanced Materials ] (]]]]) ]]]–]]] Please cite this article as: R.-J. Xie, N. Hirosaki, Sci. Technol. Adv. Mater. (2007), doi:10.1016/j.stam.2007.08.005