Luminescent Properties Of Tb～(3+)-activated Green Phosphors Under VUV-UV Excitation

The study of VUV phosphor becomes more extensive recently as the VUV phosphor is increasingly used for mercury-free lamps and the Plasma display plate(PDP). In order to improve the luminescent efficiency of the phosphors under high energy vacuum ultraviolet radiation (VUV) exciting, the properties of the host absorption band and the absorption of 4f5d states and the energy transfer in the systems have been studied. The aim of this paper is mainly in research of the spectroscopic characteristics and the luminescent mechanisms of the electronic transitions at 4f levels and 4f5d states of rare earth ions under VUV and short wavelength ultraviolet (UV) exciting, the energy transfer, the properties of the host absorption band, the factor that affect luminescence properties, and to find the routes of increasing the luminescent efficiency of the VUV phosphor by different synthesis methods. The main results obtained are as follows:A. The properties of the host absorption band in the range of VUV are studied, which of the rare-earth orthophosphate and aluminate doped with Tb³⁺, and properties of the absorption band of the Tb³⁺ ion's 4f-5d transition. The products prepared by solid-reaction method show that the host absorption band of GdPO₄:Tb³⁺ was observed around 157nm. And a broad host absorption bands of SrAl₂O₄:Tb³⁺ was observed firstly between 140nm and 168nm. Simultaneously, the excitation spectrum reveals that the absorption band of the Tb³⁺ 4f-5d transition is roughly in the range between 173nm and 240nm in GdPO₄:Tb³⁺. For SrAl₂O₄:Tb³⁺, it is in the range between 205 and 260nm. The strong host absorption band in the VUV region from excitation spectra of Tb³⁺ ion means that the energy transfer between the doped ion and the host occurred. It could be concluded that the existence of the strong broad absorption bands in the VUV region could enhance the potential of these phosphors as good candidates for mercury-free lamps and plasma TV application .B. The energy transfer between Gd³⁺ and Tb³⁺ ions, Gd³⁺ and Er³⁺ ions for both systems of GdPO₄:Tb ³⁺ and SrAl₂O₄:Tb³⁺,Gd³⁺ was studied. The energy transfers between Gd³⁺ and Tb³⁺ ions were all observed. In particular, the energy transfer between Gd³⁺ and Er³⁺ ions in GdPO₄:Er ³⁺ was found firstly. Mechanisms of energy transfer have also been studied.C. The phenomena of the fluorescence quenches in GdPO4 co-doped with Er³⁺and Tb³⁺ was observed. To compare the emission spectra of GdPO₄:Tb³⁺ with those of GdPO₄:Tb ³⁺, Er³⁺ ,we could see the intensity weakened of 5D4 -7Fj transition peaks of Tb³⁺ in GdPO₄:Tb ³⁺, Er³⁺. And it was first time to interpret the possible origins of the fluorescence quenches after doping Er³⁺ ion.D. The phase compositions and the spectra properties of SrAl₂O₄:Tb³⁺ under VUV and short wavelength ultraviolet (UV) exciting by conventional solid-reaction method and combustion synthesis method were studied. By contrast we found firstly that samples of SrAl₂O₄:Tb³⁺ was a kind of phosphors with high luminescent efficiency by the two-step combustion synthesis.