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The improvement of moisture stability of yellow phosphor encapsulated with SiO2

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During the past decades the phosphor materials have attracted much attention because of interesting optical and structure properties. They have been studied and applied in many fields such as cathoderay tubes (CRTs), flat panel displays (FPDs), fluorescent lamps, X-ray detectors, light emitting diodes (LEDs) and more. However due to the environmental factors, unmodified phosphors are sensitive to environmental conditions such as moisture, temperature and charging [1÷5]. In addition, unmodified phosphor particles will conglomerate because of the surface electricity charging. This sensitivity limits the utility of the phosphors. Thus an effective protection method of each of such inorganic material from moisture and environmental conditions would be highly desirable. Numerous attempts have been made to enhance the chemical stability of phosphor particles, by changing synthesis parameters or by mixing the phosphor with another compound. Also a surface coating using nanoparticles has been frequently applied to enhance the chemical stability of several phosphors. The qualified coating must meet basic requirements: complete coverage of the particles with thin and transparent layer and should protect core material from environmental factors and working conditions without loss of optical properties. A number of techniques have been used to coat particles namely mechanical milling, atomic layer deposition (ALD) [6], pulsed laser ablation (PLD) [7], sol-gel [8÷10] etc. In these techniques, sol-gel is the most favourable one because this technique puts forward excellent control of stoichiometry, density and microstructure. There have already been some reports on protective coating of phosphors so far. Due to reports from literature, organic coating [11, 12] and inorganic coating [4, 13] was proposed to improve the phosphor. Whereas organic encapsulation can fulfil the moisture resistance it fails when higher temperature is applied hence [...]

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