Synthesis And UV-VUV Photoluminescence Of Two Typical Tungstate Hosts Activated By Eu³⁺

The commercial red emitting phosphor (Y, Gd) BO3:Eu3+has high luminescent efficiency under vaccum ultraviolet (VUV) excitation, but its color purity isn't satisfied with the applications because of the inversion symmetry of Eu3+sites. Hereby, it is a urgent task for scientists to search for new red VUV materials.Tungstates are considered as very potential in practice due to their good chemical stable, simple preparing conditions and high luminescent intensity. The investigation on the luminescent properties of tungstates activated by Eu3+, which is significative both on the scientific research and in practice.In our paper, two new luminescent host (KGd (WO4)2 and CaWO4) which are synthesized by solid-state reaction are employed in the experiment. Their luminescent properties are investigated under ultraviolet (UV) and VUV. The results have been presented as follow,VUV light excites majorly the host lattice of KGd (WO4)2:Eu3+. The excitation energy can be absorbed by WO42-and the charge transfer transition of O2--Gd3+, the absorbed energy is transferred to Eu3+by Gd3+. Then Eu3+is relaxed to the 5D0 level and transits to its 7Fj levels emitting a photon in the red visible spectral region. The luminescent intensity of KGd(WO4)2:Eu3+in VUV region is enhanced by co-doping MoO42-. Because there is energy transfer between WO42- and MoO42-. Then the absorbed energy is transferred effectively to Eu3+by Gd3+and MoO42-.Viz, MoO42- is a sensitizer. Therefore, the emission intensity is improved by introducing MoO42-. The emission intensity of KGd0.45 (WO4)1.8(MoO4)0.2:Eu3+0.55 is about 60%of the commercial red phosphor (Y, Gd) BO3:Eu3+under 147 nm excitation.CaWO4:Eu3+can efficiently absorb the excited energy by WO42- in the VUV region and the maximum of WO42- absorption band locates at 163 nm. The intensity of CaWO4: Eu3+phosphors can be increased by introducing Na+. Because the Na+acts as a charge compensator and decreases the defects in CaWO4:Eu3+. When the Bi3+is introduced into the CaWO4:Eu3+, the excitation energy can be absorbed by WO42- and Bi3+. Then the absorbed energy is transferred to Eu3+by Bi3+. Viz, Bi3+can sensitize the luminescent intensity of Eu3+under 147 nm excitation. The best phosphor is CaWO4:Eu3+0.04, Bi3+0.04 and its integral intensity is about 25%of the commercial red phosphor (Y, Gd) BO3:Eu3+.