PDF Publication Title:
Text from PDF Page: 120
84 Handbook on the Physics and Chemistry of Rare Earths synthesized the same phosphor as follows: a mixture of a-Si3N4, AlN, CaO, and Eu2O3 was put into a boron nitride crucible and heated in pressurized nitrogen atmosphere using a resistance heating furnace. Solid-state reaction processes are applied to produce many commercially available phosphors: eg, Sr2Si5N8:Eu2+ (Li et al., 2006a,b), CaAlSiN3:Eu2+ (Uheda et al., 2006a,b), or b-SiAlON:Eu2+ (Hirosaki et al., 2005) for ins- tance. The raw materials for alkaline-earth-containing nitride phosphors, eg, Sr2Si5N8:Eu2+ and CaAlSiN3:Eu2+, are usually handled in a glove box filled with inert gas because unstable alkaline-earth nitrides (ie, Sr3N2 or Ca3N2) are used as raw materials. On the other hand, the raw materials for some oxygen-containing nitride phosphors (called oxynitride phosphors) can be handled in air because they do not contain unstable alkaline-earth nitrides. For example, SrSi2O2N2:Eu2+ can be synthesized from a mixture of SrCO3, SiO2, Si3N4, and Eu2O3, without using Sr3N2 (Li et al., 2005). 2SrCO3 +SiO2 +Si3N4 !2SrSi2O2N2 +2CO2 As for the SrSi2O2N2:Eu2+ phosphor, a two-step synthesis was reported to improve the luminescence properties of the phosphor, ie, (Sr,Eu)2SiO4 was synthesized first and then reacted with Si3N4 to obtain the targeted phosphor (Yun et al., 2007). It has been proposed that compounds other than nitrides can be used as the raw materials. For example, calcium cyanamide (CaCN2) is used to synthesize the CaSrSi5N8:Eu2+ phosphor (Piao et al., 2008), ie, a mixture of CaCN2, SrCO3, Si3N4, and Eu2O3 is put into a boron nitride crucible and heated at 1823 K. 5.2.4 Gas Phase Reduction and Nitridation The gas phase reduction and nitridation method is a synthetic process in which nitridation of easily available raw materials other than nitrides (eg, oxides) and synthesis of the phosphor are conducted simultaneously by the effect of reactive flowing gases. For example, europium-activated Ca-a0-SiAlON was synthe- sized by the following procedure (Suehiro et al., 2005): Ca–Al–Si–Eu mixed oxide, which is prepared by coprecipitation using CA, was placed in a tubular furnace and heated at 1350–1500°C under a flow of NH3 and CH4 gas mixture. Another example is the synthesis of LaSi3N5:Eu2+ phosphor. A mixture of La2O3, CeO2, and SiO2 was heated twice at 1350 and 1450°C under a flow of NH3 and CH4 gas mixture (Suehiro et al., 2009). In these reactions, NH3 and methane react with the oxide raw materials, reducing and nitridating them to yield the desired phosphors. Using this method, nitride phosphors can be synthesized from easily available oxides and/or carbonates without expensive nitride raw materials. 5.2.5 Carbothermal Reduction and Nitridation Another synthetic method for obtaining nitride phosphors by simultaneously conducting reduction and nitridation during heating is the carbothermalPDF 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 | RSS | AMP |