Preparation Of Hexaaluminate Phosphors And Their Luminescence Properties

Phosphors based on hexaaluminates have attracted a great deal of attention because of their application in plasma display panels (PDPs) and Hg-free lamps, among which BaAl₁₂O₁₉:Mn²⁺ and BaMgAl₁₀O₁₇:Eu²⁺ (BAM) have been widely used as commercial phosphors. However, the former's luminescence efficiency, decay time and the latter's stability still need to be improved to fulfill the demands of the development of PDPs and Hg-free lamps. Accordingly, these two phosphors were studied systematically in this thesis. Furthermore, the luminescence properties of Dy³⁺ activated LaMgAl₁₁O₁₉ under vacuum ultraviolet (VUV) and UV excitation were also preliminarily investigated for the potential application in Hg-free lamps and LEDs of Dy³⁺ activated phosphors. The results derived from the above research would contribute greatly to the understanding of the luminescence mechanism of hexaaluminate phosphors and advance their application in PDPs and Hg-free lamps.1. The host of BaAl₁₂O₁₉ can efficiently transfer the energy to the luminescent center of Mn²⁺ under VUV excitation. By analyzing the VUV excitation spectra of Bao.75AlnO17.25-x BaMgAl₁₀O₁₇:0.1 Mn²⁺ solid solution, the optical absorption positions of the groups of AlO₄^5-, AlO₆^9- and MgO₄^6- in the spinel blocks were assigned, which would lay a solid foundation for the study of the luminescence mechanism of BaAl₁₂O₁₉:Mn²⁺ and other commercial hexaaluminate phosphors and the improvement of their VUV luminescence properties.2. Because of the doubly spin and parity-forbidden ⁴T₁→⁶A₁ transition of Mn²⁺, the decay time of BaAl₁₂O₁₉:Mn²⁺ is still somewhat too long for its application in PDPs. In this thesis, the influences of the concentration of Mn²⁺ on the luminescence properties of Ba_0.75Al_11-xO_17.25:x Mn²⁺ were studied. The results indicates that increasing the concentration of Mn²⁺ properly can decrease the decay time to some extent avoiding the deterioration of color purity and brightness. According to the results of EPR and Mossbauer Spectroscopy, it is considered that Mn²⁺ paired centers are formed by Mn²⁺ occupying Al(2) sites in Ba_0.75Al₁₁O_17.25 and thus induce the variation of luminescence characteristics.3. The influences of the co-doping of ns² ions and Zn²⁺ on the luminescence characteristics of BaAl₁₂O₁₉:Mn²⁺were evaluated in this thesis. The results indicates that the co-doping of Bi³⁺, Sb³⁺ and Zn²⁺ can effectively enhance the luminescence intensity of BaAl₁₂O₁₉:Mn²⁺, among which the co-doping of Sb³⁺ is the most effective. The co-doping of these three kinds of ions didn't show obvious effects on the decay behavior of BaAl₁₂O₁₉:Mn²⁺.4. Mn²⁺ activated barium hexaaluminate nanophosphors with spherical and rod-like morphologies were successfully synthesized by a reverse microemulsion method combined with a precipitation process, and their luminescence properties under VUV excitation were investigated for the first time. The luminescence intensity, brightness and color purity of Ba_0.999Al_11.9O₁₉:0.1 Mn²⁺, 0.001 Eu²⁺ spherical nanophosphor are better than those of bulk BaAl_11.9O₁₉:0.1 Mn²⁺; the critical Mn²⁺ concentration ofBa_0.75Al_11-xO_17.25: Mn²⁺ spherical nanophosphor is higher than bulk counterpart; the particle morphology has great impact on the luminescence properties of Mn²⁺ activated barium hexaaluminate nanophosphors.5. BAM particles were successfully coated with MgF₂ and CaF₂-coatings by a sol-gel process. The results indicate that the thermal stability of coated BAM is obviously improved and the effect of MgF₂-coating is better than that of CaF₂.6. The luminescence properties of LaMgAl₁₁O₁₉:Dy³⁺ co-doped with Bi³⁺, Sb³⁺and Zn²⁺ in UV-VUV region were preliminarily studied for the first time. The results exhibit that Dy³⁺ activated LaMgAl₁₁O₁₉ shows white-light emission under a variety of wavelength excitation (147 nm, 254 nm and 365 nm). The co-doping of Bi³⁺ and Zn²⁺ can both sensitize the emission of Dy³⁺ under the above three excitation sources with the movement of chromaticity coordination towards the yellow region, and the sensitizing effect of Bi³⁺ is better than that of Zn²⁺.