PDF Publication Title:
Text from PDF Page: 099
Rare Earth-Doped Phosphors for White LEDs Chapter 278 63 (Ruan et al., 2011). SrAlSi4N7:Eu2+ phosphors have a strong absorption band ranging from the UV to the visible, efficiently excitable by a blue light. A broad red emission band with a peak at 625 nm can be seen, and the exter- nal quantum efficiency is $49% under excitation at 460 nm. At 150°C, the emission intensity under excitation at 460 nm is $83% of that at room temperature. 4.3 Sulfides and Oxysulfides (Oxy)sulfide phosphors have been used in electro- and cathode luminescence. There consist in blue-light excitable materials such as AES:Eu2+ (AE 1⁄4 Ca and Sr) and AEGa2S4:Eu2+ (AE1⁄4Ca and Sr) with strong covalent character of the sulfide ions. Since most of the sulfide phosphors have poor chemical stability with respect to humidity, protection of the phosphor particles by a coating layer is required. 4.3.1 AES:Eu2+ (AE1⁄4Ca and Sr) Phosphors Rare earth-doped alkaline-earth sulfide materials are well-known phosphors for electroluminescent and cathodoluminescent displays as well as for electron trapping optical memory materials (Ando and Ono, 1990; Choi et al., 1998; Kato and Okamoto, 1983; Pham-Thi and Ravaux, 1991; Wu et al., 2002). Among the alkaline-earth sulfide phosphors, CaS- and SrS-based phosphors have attracted great attention due to their potential for applications in displays (Collins and Ling, 1993; Kravets, 2001; Pham-Thi and Ravaux, 1991). In particular, Eu2+-activated AES (AE1⁄4Ca and Sr) have recently been recon- sidered to be one of the promising red phosphor candidates for white LEDs (Guo et al., 2006; Hu et al., 2005; Kim et al., 2006; Yang et al., 2014a,b). They have a well-known cubic rock-salt structure with space group Fm3m (a1⁄40.5695 nm for CaS and a1⁄40.6020 nm for SrS). The Ca2+ and Sr2+ ions form (Ca/Sr)S6 octahedra where the Ca–S and Sr–S bond distances are 0.2845 and 0.2900 nm, respectively. Both CaS:Eu2+ and SrS:Eu2+ have a broad optical absorption band in the visi- ble ranging from 400 to 600 nm and exhibit a broad red emission peaking at 610 nm in SrS:Eu2+ and at 650 nm in CaS:Eu2+ (Hu et al., 2005), as shown in Fig. 60. An all-proportional solid solution can be formed between CaS and SrS, making it possible to tune the emission color via controlling the Ca/Sr ratio. Unfor- tunately, (Ca,Sr)S:Eu2+ phosphors are known to exhibit large thermal quenching. Actually, with increasing temperature up to 150°C, the emission intensity of SrS: Eu2+ decreases by more than 40% of that at room temperature (Kuo et al., 2010b). Recently, Yang et al. (2014a,b) succeeded to improve considerably the thermal quenching resistance of CaS:Eu2+ by doping it with small amounts of Mg and Ga. At 150°C, the emission intensity of Ca0.89Mg0.01Ga0.1S:Eu2+ reaches 75% of that measured at room temperature. The Mg and Ga doping also results in significant enhancement of the emission intensity at room temperature.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)