This study fully investigated the vacuum ultraviolet excitation spectra of pure and rare-earth（RE=Eu, Tb and Dy）-doped A2Zr（PO4）2（A=Li, Na and K） phosphors. The synthesized Na and Li compounds were characterized by XRD showing two new types of phases after indexation. Although these three pure compounds had different crystal structures, they exhibited similar luminescence properties. For Eu3＋-activated samples, the broad excitation band centered at 217 nm could be attributed to the CT transition between O2–（2p6） and Eu3＋ ions. For Tb3＋-doped samples, two groups of f-d transitions were observed, where a strong broad band at 221 nm was due to the spin-allowed f-d transition. Energy transfer from O2– to Dy3＋was not observed in Dy3＋-doped phosphors, probably because it overlapped considerably with the CT transition from O2– to Zr4＋ at 187 nm.
Thermal annealing of YOH1.1F1.9 and YOH1.1F1.9：Ln3＋ （Ln3＋=Eu3＋, Tb3＋ and Gd3＋） precursors in air gave access to synthe- size yttrium oxyfluoride phosphors with well-preserved needle-like morphologies. The phase purities of samples strongly depended on the thermal annealing temperature. At 600 ℃, pure Y5O4F7 with orthorhombic structure were obtained, as evidenced by powder X-ray diffraction measurement and chemical analysis. The interesting microstructure evolution of the annealed sample from well-organized nanoparticles on curly slices to microrod-bundle structure had been aroused by raising annealing temperature. The multicolor fluorescent emissions of Y5O4F7：Ln3＋ phosphors were observed, e.g. ultraviolet emission for Gd3＋, green emission for Tb3＋ and red emission for Eu3＋, which resulted from characteristic transitions of different lanthanide ions.
LIU BiqiuLIU LishaGUO KaiWANG JiaoZHU LinlinZHANG HuiWEN WenYANG TieyingZHAO Jingtai
