Exploration On Blue-Excited Phosphor Materials

The blue-exciting phosphors doped with rare earth or transition metals have been synthesized by different methods. We also investigated the crystal structure and luminescence properties of these phosphors in this dissertation. The main progress as follows,The YAG: Ce³⁺ phosphors were prepared with the sol-gel method. The influences of synthesized temperatures, reaction atmosphere, and concentrations of doped Ce³⁺ and Gd³⁺ on the luminescent properties were systematically studied. The crystal field splitting changes with the increasing content of doped Ce³⁺. Thus, the emission wavelength firstly shifted to red region and then to blue. The YAG: Ce³⁺ phosphor with highest emission intensity was prepared by calcinations the precursor with twenty time of urea to that of metal cations at temperature range of 1400¹500 in a reduction atmosphere.Rare-earth doped Me-α-SiAlON andβ-SiAlON samples were prepared and the photoluminescence spectra of these phosphors were also studied. With the increasing of doped Y³⁺ content, the rigidity ofα-SiAlON lattice was decreased since the short and stable Si-N bonding was replaced by the weak Al-N bonding. Therefore the emission energy origined from the 5d→4f transition was reduced, which resulted in the red-shift of emission and excitation spectra. The broad-band emission caused by the strong crystal field splitting was also observed. The luminescence properties of lanthanum silicon oxynitride (La-Si-O-N) series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications. The mechanism of photoluminescence was discussed from nephelauxetic effect, splitting of crystal field and covalency of Ce-N bond. The luminescence of Ce³⁺ in La-Si-O-N covered the band from ultraviolet to blue, and the excitation bands ranged from 250 nm to 400 nm which still located in ultraviolet region. The effort for the exploration using Ce³⁺ luminescence center in blue-activated phosphors should be made to focus on the crystal field effect.The glass samples, MeO-Al₂O₃-B₂O₃: Eu²⁺ (Me=Mg, Ca, Sr, Ba), excited by the blue light, was synthesized. The effect of preparation process on the luminescence, including content of B₂O₃, annealing time and different Me atoms, was also studied. The crystal structure of MeSi₂O₂N₂ (Me=Ca, Sr) was characterized. And the luminescence mechanisms of Eu²⁺-activated CaSi₂O₂N₂ and Yb²⁺-actived SrSi₂O₂N₂ was also discussed. Pr³⁺-activated blue-green phosphor and Eu³⁺-activated red phosphor hosted in MgGa₂O₄ spinel have been prepared by a gel-assisted high-temperature calcinations process, respectively. The results indicated that trivalent Pr and Eu ions can be incorporated into mixed spinel MgGa₂O₄ up to ⁴% by the formation of both anion and cation vacancies. The incorporation effect activates the electron transition from the host lattice to the sole energy level of ³P0 of Pr³⁺ and ⁵D0 of Eu³⁺, which hresults in a strong and monochromatic emission in blue-green (Pr) and red (Eu) bands.