| Luminescent materials can absorb the high energy ultraviolet (UV) or blue light and convert them into visible light with relatively low energy. The luminescent materials play a very important role in the White Light Emitting Diode (w-LED) due to the energy saving, high emission efficiency, and environment friendly characteristics. This promotes the investigation of luminescent materials with high performance. Now days, the most common luminescent material is aluminate phosphors, which process excellent optical properties, low production cost, high physical and chemical stabilities. And due to the development of new LED lighting and display technologies, the aluminate phosphor with small particle size and high emission intensity has attracted much attention among the researchers in recent years. It is very hard for the traditional solid-state reaction method to achieve the phosphor products with small particle size, because the high synthesis temperature is necessary to eliminates impure phase during the synthetic process, and this will also cause an easily agglomeration in final products. The liquid-phase synthesis method can achieve the precursor with high homogeneity and reactivity, thus the pure phase phosphor products with small particle size will be achieved under the lower temperature. However, due to the reactions in the liquid phase, such as precipitation, hydrolyzation and complexation, the raw materials must be carefully selected. In some situation, the organic compound must also be used to assist the preparation of precursor. This will improve the production cost and make the synthetic procedure more complex and uncontrollable. Thus, in chapter Ⅱ, we proposed a facile sol-gel method to synthesize the YAG:Ce phosphor, and no organic additives have been used. The hydrolyzation and complexation of Al(NO3)3·9H2O will dissolving other oxide materials, and form the gel with high homogeneity. The achieved Y3Al5O12Ce3+ (YAG:Ce) phosphor exhibits higher emission intensity and the particle size are much smaller than that of the commercial one. In chapter III, a more convenient method for the synthesis of aluminate phosphors has also been proposed. High performance BaMgAl10O17Eu2+ (BAM:Eu) phosphor was achieved through an aqua-suspension method, based on the surface charge interaction of starting powders with the aid of the γ-Al2O3 porous structure. The obtained BAM:Eu product exhibits a higher emission efficacy compared to the commercial samples, and suitable to be applied in many devices.There are also some disadvantages on aluminate phosphors, for example, the color rendering property (CRI) of the YAG:Ce phosphor has been limited due to the low red light component in emission spectrum. Therefore, the optimization of the aluminate phosphors is very important for its applications in lighting and display devices. In chapter IV, the Eu2+ doped YAG phosphor has been firstly synthesized by the sol-gel method mentioned in the second chapter with the assistance of the hydrogen iodide (HI). The achieved YAG:Eu2+ phosphor can be excited by the UV light and emits blue light, shows a potential application in W-LED based on the UV light chips. For aluminate phosphors, Al-0 pairs in host lattice can be substituted by Si-N pairs due to the similar bond lengths and bond characters, and the activator coordinated with N3- will shift the emission spectra to the longer wavelength. Thus, the incorporation of Si-N into YAG:Ce phosphor has been considered as a effective way to improve the CRI of W-LED devices. Usually, the Si3N4 has been used to achieve the Si-N co-doped YAG.Ce phosphor, however, the pore reactivity of the Si3N4 has limited effects to the doped sample, and even lead to a decrease of the emission efficiency and thermal stability. In chapter V, Si-N co-doped YAG:Ce phosphor has been successfully prepared by a solid-state reaction method using CeSiO2N as one of the raw materials. The achieved product exhibits increased red light component and better thermal quenching property. Moreover, an evident long afterglow luminescence was detected for the first time. The strong covalent Ce-N and Si-N bonds in CeSiO2N allow more Ce3+ ions to be coordinated to N and also favor a homogeneous distribution of Si-N in the host lattice.Recently, the blue laser diode has been considered as an emerging excitation lighting source for the devices willing to achieve super-high brightness and wider color gamut. Thus the thermal conductivity of color converter (phosphor) needs to be high enough to dissipate the heat generated by the high-power laser lighting quickly. The phosphor-in-glass (PiG), where a certain amount of phosphor powders are dispersed in a glass matrix, is considered as a suitable color converter for high power blue laser lighting due to the high thermal conductivity. In chapter Ⅵ, we reported a green-emitting PiG material by co-firing β-Sialon:Eu2+ phosphor powders with the glass frits. The β-Sialon:Eu phosphor powders were homogeneously dispersed in glass matrix and the interfacial reactions have not been observed. And for the first time, the optical properties of the green-emitting PiG material were evaluated and discussed when it was excited by the blue laser lighting.In chapter Ⅶ, we have summarized the research works mentioned above and provided some suggestions for the future works. |
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