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72 Handbook on the Physics and Chemistry of Rare Earths ex. 1 0.5 0 em 300 400 Wavelength (nm) Excitation and emission spectra of (Ca,Sr)7(SiO3)6Cl2:Eu2+. Redrawn from Daicho, H., Iwasaki, T., Enomoto, K., Sasaki, Y., Maeno, Y., Shinomiya, Y., Aoyagi, S., Nishibori, E., Sakata, M., Sawa, H., Matsuishi, S., Hosono H., 2012. A novel phosphor for glareless white light-emitting diodes. Nat. Commun. 3, 1132. Ca/Sr 1⁄4 0.55/0.45. The M1 site (indicated by blue octahedron circle in Fig. 69) adopts sixfold oxygen coordination, forming CaO6 octahedra that, together with SiO4 tetrahedra, construct a Ca(SiO3)6 framework. The M2 site (indi- cated by purple spheres in Fig. 69) adopts eightfold coordination with seven oxygen and one chlorine atoms. The M3 site (indicated by yellow spheres in Fig. 69) adopts sevenfold coordination with five oxygen and two chlorine atoms. From Rietveld refinement, it is clear that Eu2+ ions substitute both for the M2 and M3 sites. Cl_MS:Eu2+ shows a strong absorption band in the near-UV region, extending from 370 to 420 nm and exhibits a strong broad emission band peaking at $580 nm (Fig. 70). The highest emission intensity of the phos- phors is obtained for (Ca0.37Sr0.53Eu0.10)7(SiO3)6Cl2, the internal quantum efficiency of which is 94% under excitation at 407nm. Furthermore, Cl_MS:Eu2+ has an excellent thermal stability with respect to temperature quenching: the emission intensity measured at 150°C is 94% of that at 25°C. 4.4.2 Oxyfluorides 4.4.2.1 (Sr,Ba)3AlO4F:Ce3+ Phosphors (Sr,Ba)3AlO4F belongs to the Cs3CoCl5-family structure and is isostructual with Ba3MO5-type materials (M1⁄4tetravalent metal) (Glasser and Glasser, 1965; Drofenik and Golic, 1979; Im et al., 2010, 2011). Fig. 71 shows the crystal structure of (Sr,Ba)3AlO4F with space group I4/mcm. The Sr and Ba atoms are surrounded by two F and six or eight O atoms, respectively. The FIG. 70 500 600 700 Normalized intensity (a.u.)PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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