Site-Occupancy And Energy Transfer Of Luminescence Centers In Phosphate Phosphors

Rare earth doped phosphate phosphors are widely used in lighting and display field because of their outstanding chemical and thermal stability, low price of raw materials, mild synthetic conditions and other advantages. In recent years, especially with the rising popularity and promotion of white LED, new research and application of rare earth ions doped phosphate luminescent material is on the rise. In order to satisfy the demand of the white LED phosphors, this paper chose two kinds of new phosphate as matrix material, using rare earth ions or transition metal ions as activator, and prepared a series of phosphor samples by high temperature solid state method. The as-prepared phosphors can be excited effectively by near ultraviolet light （n-UV）. This thesis systematically studied the crystal structure, site occupancy of rare earth ions, photoluminescence property and energy transfer mechanism, etc.First, we use the high temperature solid state process to synthesize a novel phosphate phosphor Ca₁₀（PO₄）₆O:Ce³⁺, and analyze its crystal structure by GSAS Rietveld refinement method. By changing the Ce³⁺-doping concentration, the emission colors of Ca10（PO4）60:Ce³⁺ can be changed from blue to yellowish-green light. The corresponding luminescent mechanism was discussed.Furthermore, Ce³⁺ and Eu²⁺/Tb³⁺/Mn²⁺ ions codoped Ca₆Ba[₄O₁₇ （CBPO） phosphors were also prepared via a high-temperature solid state reaction. The structural refinement indicates that the as-prepared phosphors crystallize in monoclinic phase with space group C2/m and there are two Ca sites and one Ba site in host lattice. The doping ions are determined to occupy Ca sites and the emission of Ce³⁺ and Eu²⁺ ions at different Ca sites in the CBPO host have been identified and discussed. Since bright blue and yellow emissions were observed from Ce³⁺ and Eu²⁺ ions in the CBPO under n-UV excitation, respectively. They were codoped into the CBPO for designing energy transfer from Ce³⁺ to Eu²⁺ to improve the luminescence efficiency of Eu²⁺. In addition, Tb³⁺ ions were added into the CBPO:Ce³⁺ system for realizing highly efficient green emission. The energy transfer mechanisms from Ce³⁺ ions to Eu²⁺/Tb³⁺ ions were discussed. Interestingly, the incorporation of Mn²⁺ into the CBPO:Ce³⁺ system can enhance the blue emission of Ce³⁺ ions due to the modification of crystal lattice. Finally, the thermal stability of CBPO:Ce³⁺, Eu²⁺/Tb³⁺/Mn²⁺ phosphors have been investigated systematically and corresponding mechanisms were proposed. Based on these results, the as-prepared CBPO:Ce³⁺, Eu²⁺/Tb³⁺/Mn²⁺ phosphors can act as potential blue, yellow, green, and emission-tunable phosphors for n-UV based white LEDs.