**2. Effects of sintering fluxes on morphology**

BaMgAl10O17:Eu2+ (BAM:Eu) phosphor is an important blue-emitting phosphor and has found widespread applications in plasma display panels (PDPS) and fluorescent lamps. The BAM phosphor powders synthesized with individual flux materials, such as AlF3, NH4F, LiF, and so on, have been found to exhibit different morphologies. Flux materials are usually compounds of alkali- or alkaline earth metals with lower melting temperatures than that of the host. In this study, BaMgAl10O17:Eu2+ phosphor was prepared with fluxes by spray drying and post-treatment processes. The phosphor prepared with combination of KF and H3BO3 resulted in fairly uniform hexagonal plate-like morphology **(Fig. 2),** and the morphology as well as the plate size is actually in between those obtained by each of these fluxes. However, the phosphor prepared with the combination of KF and NaCl gives particles showing two distinct morphologies, including thin hexagonal plates and rounded particles **(Fig. 3).** These morphologies had appeared to be a mixture of the products

Fig. 2. SEM photographs of the BAM : Eu phosphor prepared with KF and H3BO3 **[1].**

Fig. 3. SEM photographs of the BAM : Eu phosphor prepared with KF and NaCl **[1].**

The Role of Sintering in the Synthesis of Luminescence Phosphors 327

powders. The sintering temperature was optimized to be 1200 °C. The luminescence intensity of CaAl2O4:Eu3+ was significantly enhanced by co-doping with alkali metal ions, probably due to the charge compensation. Furthermore, the emission intensities were gradually enhanced when the radius of R+ became smaller from K+ to Li+ ion. It was probably due to the difference of ionic radii which would give rise to the diversity of sublattice structure around the luminescent center ions. This fundamental work might be important in developing new luminescent devices applicable for tricolor lamps, light

In Y2O3:Eu sintered at 700-12000C in air, Li2CO3 flux was found to: (i) enhance the crystalline growth, ii) improved the grain size slightly morphology from a plate like structure to spherical shape, and iii) improved significantly its PL sensitivity. The optimal red PL was achieved when the Y2O3:Eu3+,Li+ phosphor was synthesized using 11 mol% Eu2O3 and 70

In ZnWO4, the maximum PL intensity was obtained when the sintering temperature was 1,100°C. A significant decrease in PL intensity was measured when the phosphor was sintered at 1,200°C. This decrease was attributed to a change in the crystallinity of the phosphor, in which (020) ZnWO4 was the dominant crystalline phase. Empirically, the change in crystallinity alters the emission mechanisms of the phosphor. The growth of larger phosphor grains was another reason for the decrease in luminescence. Furthermore, the PL spectrum was broadened when the sintering temperature increased. Apparently, oxygen vacancies were involved in the phosphor crystal, and the bluish-green emission was related to electron transitions from the energy levels of the ionized oxygen vacancies to the phosphor valance band. The concentration of oxygen vacancies usually increases with an

Significantly, on UV illumination, a white-light phosphor could be achieved if the bluish-

Combined co-precipitation with the molten salt method, a new technology for preparation of Y2O3:Eu3+ and YAG:Ce3+ phosphors was proposed with the controlled size and higher luminescent intensity. With rare earths oxide as raw materials, the molten salt method was compared with solid phase method. Some main principles for the selection of molten salt system were, i) the melting point should lower the temperature of phosphor preparation, ii) the difference of boiling point and melting point should be as wide as possible, and iii) the molten salt must not be hazardous to luminescent intensity. The best multiple molten salt system for Y2O3:Eu3+ and YAG:Ce3+ were NaCl+S+Na2CO3 and Na2SO4+BaF2, respectively **[2].** Molten salt sintering improved the crystal degree and configuration of phosphors, resulting in higher luminescent intensity. Using YCl3 and EuCl3 as raw material, the preparation of Y2O3:Eu3+ precursor was investigated concerning some factors, such as temperature, complexing agent, precipitation agent and the dripping mode. The size of precursor was the smallest at pH=7 and the complexing agent could control the release velocity of rare ion effectively. With citric acid as a complexing agent, the size of precursor and sintering sample was the smallest and the luminescent intensity of sintering sample was

increase in sintering temperature and a broadened emission is thus observed.

green ZnWO4 and red Y2O3:Eu3+,Li+ phosphors were blended.

emitting diodes and other fields.

**4. Molten salt sintering** 

mol% Li2CO3 and sintered at 1,200°C for 5 h.

resulting from each individual of the two fluxes. These powders show different photoluminescence (PL) intensities. To sum up, by selecting distinct individual or binary fluxes, the morphologies, particle size, and the PL intensities of BAM phosphor can be controlled. Beside, both larger crystal size and appropriate aspect ratio play a crucial role on enhancing the luminescence of BAM phosphor.
