PDF Publication Title:
Text from PDF Page: 076
40 Handbook on the Physics and Chemistry of Rare Earths 4.2 (Oxy)nitrides There are little practical phosphors among nitride and oxynitride materials except those for LED phosphors. Red-emitting ability of excitation and emis- sion wavelengths is sometimes desired in order to change their color chromatic- ity. This can be achieved by partially or fully substituting nitride ions for oxide ions, bringing about an increase in covalent bond character. (Oxy)nitride phos- phors can be classified into two groups, nitridosilicates and nitridoaluminosili- cates, the frameworks of which are composed of Si(N,O)4 and Al(N,O)4 tetrahedral units, respectively. Many nitrides are easily hydrolyzed by air mois- ture and, therefore, chemically stable nitrides and oxynitrides are rare. 4.2.1 Yellow-Emitting Phosphors 4.2.1.1 Ca-a-SiAlON:Eu2+ Phosphors The name SiAlON is given to ceramics composed of the elements Si, Al, O, and N. They have two morphologies, a- and b-SiAlONs, which are solid solutions based upon structure modifications of a- and b-Si3N4, respectively (Xie and Hirosaki, 2007; Xie et al., 2010). The general formula of a-SiAlON can be given as MxSi12(m+n)Alm+nOnN16n (x1⁄4m/v, where v is the electric valence of metal M) and b-SiAlON can be described by Si6zAlzOzN8z. Both materials have turned out as excellent host materials for Eu2+- or Ce3+-activated phosphors for white LEDs with high luminescence efficiency under blue light excitation (Gan et al., 2013; Xie and Hirosaki, 2007; Xie et al., 2010). Among them, Eu2+-activated Ca-a-SiAlON is one of the yellow-emitting phosphors used in white LEDs (Xie et al., 2004a). The crystal structure of Ca-a-SiAlON with space group P31c is shown in Fig. 36. Although it is similar to that of a-Si3N4, the unit cell volume is much larger owing to the incorporation of Al, O, and Ca (Jack and Wilson, 1972; Petzow and Herrmann, 2002). Namely, the structure of Ca-a-SiAlON is built up of (Si,Al)N4 tetrahedra to form a 3D framework with corner sharing of tetrahedra. Ca2+ ions occupy interstitial sites and have sevenfold anion (N/O) coordination (Izumi et al., 1982) and the average Ca/Eu–N bond distance is 0.2612 nm. (Si,Al)(N,O) 4 Ca 0.2695(3) 0.2602(7) 0.26945(14) 0.2695(2) b a FIG. 36 Crystal structure of Ca-a-SiAlON. The unit of bond distance is nm. Pictures were drawn based on the structure data obtained from the database (ICSD #163203). 0.2361(8) 0.2602(7) 0.2602(7)PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
PDF Search Title:
HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHSOriginal File Name Searched:
Chemistry-Rare-Earths-49.pdfDIY PDF Search: Google It | Yahoo | Bing
Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)