Relationship Between Eu～(3+) Doped Vanadate Phosphors Properties And Its Crystal Structure Under Ultraviolet And Vacuum-Ultraviolet Excitation

As for the main commercial phosphors for application in plasma display panels (PDPs), the red (Y, Gd) BO₃: Eu³⁺ shows disadvantage as bad color purity, there are two ways to resolve this problem, one is to improve the performance of commercially available (Y, Gd) BO₃: Eu³⁺ mainly by enhancing its luminescence properties; the other is to investigate new red phosphors with better color purity, it is required that these new materials have strong emission line about 610 nm and have good luminescence properties. Particularly, the YVO₄:Eu³⁺ was widely considered as an ideal substitute for red component for its good optical properties such as its strong emission intensity, chemical stability and excellent color purity. However, for lack of suitable VUV light source, up to now, the main investigations corresponding to photoluminescence characteristics of vanadate phosphors were focus on UV region. As a result, there were few reports about the photoluminescence of vanadate phosphors under VUV excitation. Moreover, the photoluminescence properties of other vanadate phosphors with different structures were seldom reported, also.In order to provide a fundamental theory to develop new phosphors as well as to improve the existing phosphors, this work synthesis a serials of Eu³⁺ doped vanadate phosphors. The photoluminescence properties of vanadate phosphors such as the positions of absorption peaks, emission intensity, color purity and the energy transfer rate between activators and matrix were systemically studied. The relationship between these phosphor's photoluminescence properties and their structures were also investigated and discussed in detail. The results indicated that the gap of forbidden band for different vanadate phosphors matrix is about 2.6 eV-3.8 eV. The top of the valence band are mainly contributed by O-2p and V-3d orbits, while the bottom of conduction band are originated from the antibonding orbits which consist of O-2p and V-3d levels. The excitation peaks below 200 nm are derived from the host absorption and those above 200 nm are mainly due to the charge transfer (CT) transition of Eu-0 and some absorption of VO₄^3- groups. The law of photoluminescence intensities of different structure vanadate phosphors in both UV and VUV region is as follows: tetragonal>triclinic>monoclinic>orthorhombic. It was confirmed that the energy transfer model of vanadate phosphors excited upon UV region proposed by Blasse is also suitable for the situation under VUV excitation. The Eu³⁺ ions in all vanadate located at a non-centrosymmetrical site. As a result, the color purity of all Eu³⁺-doped vanadate phosphors is very good. In emission spectra, the emission peaks in 550-720 nm are attributed to ⁵D₀→⁷F_J(J=1, 2, 3, 4) transitions of Eu³⁺. Among them, the peak centered at 610nm is most intense and it could be assigned to ⁵D₀→⁷F₂ super-sensitive transition of Eu³⁺.