| The vaccum ultraviolet (VUV) excited phosphors activated with lanthanide ions are primarily applied in plasma display panels and mercury-free fluorescent lamps. In recent years, much work has been conducted on4fn-15d configuration from theory to experiment, for searching new VUV-excited phosphors. Energy transfer plays an very important role in improving the efficiency of phosphors, however, little study on energy transfer involving high excited states has been conducted. The4fn-15d configuration of lanthanide ions has strong absorption in the VUV region, therefore, the research on energy transfer from4fn-15d state to activators is of great significance in enhancing the efficiency of VUV-excited phosphors. The main work of this thesis is as follows:1. The luminescent properties of (La,Gd)PO4:Tb3+under VUV light excitation and the energy transfer processes between Tb3+and Gd3+are studied thoroughly. There is few report on energy transfer from Tb3+4f75d states to other ions due to the fast decay of Tb3+4f75d state. Based on the excitation and emission spectra and decay curves of (La,Gd)PO4:Tb3+, we found the occurrence of energy trasnfer from Tb3+4f75d to Gd3+; in addition, the energy transfer efficiency increases with Gd3+concentration. The efficiency is up to73%in Gd0.99Tbo.o1PO4. When Gd3+concentration is low, the decay of Gd3+6P7/2state upon Tb3+4f75d states is faster than that upon Gd3+6IJ state; the decay difference is disappearing with the increase of Gd3+concentration; the decay curves become identical when Gd3+concentration is larger than30mol%. Upon Gd3+6IJ excitation, Tb3+are randomly distributed around the emitting Gd3+, then upon Tb3+4f75d excitation, except the randonly distributed Tb3+around the emitting Gd3+, there is a Tb3+on the gound state near the emitting Gd3+. With Gd3+concentration, energy migration occurs which makes the difference upon the two ions disappear. A physical model was established upon the excitations of Gd3+and Tb3+, the decay curves were also fitted based on this model.2. In K2GdF5:Pr3+, the lowest position of Pr3+4f5d state is at45455cm-1which is lower than’So state, Pr3+is dominated by broand band4f5d state emission. The efficient energy transfer from Pr3+4f5d to Gd3+6IJ/6DJ states was observed. When Eu3+is codoped in K2GdF5:Pr3+, Pr3+4f5d energy is transferred to Eu3+through Gd3+; the energy transfer efficiency is up to96.6%with Eu3+concentration of5.0%. The decay time of5D2,3state is reducing with the increase of Pr3+concentration, a potential cross-relaxation energy transfer processes between Pr3+and Eu3+were proposed. The distribution densities of Pr3+around emiting Eu3+upon Pr3+4f5d and Gd3+6IJ states excitation were simulated. The simulation shows that the distribution density of Pr3+in short distance upon Pr3+4f5d excitation is larger than that upon Gd3+6IJ excitation, inlustrating the origin that Eu3+5D1,0/5D2,3integrated emission intensity upon Pr3+4f5d excitation is larger than that upon Gd3+6IJ excitation.3. The energy transfer processes from host to Tb3+in Na3Y(BO3)2:Tb3+'Na3Gd(BO3)2:Tb3+were investigated. In Na3Y(BO3)2:Tb3+, host excitation energy is directly transferred to Tb3+. However, in Na3Gd(BO3)2:Tb3+the host energy is mainly transferred to Tb3+through Gd3+. Upon host excitation, Na3Gd(BO3)2:10mol%Tb3+shows larger relative efficiency than that of Na3Y(BO3)2:10mol%Tb3+, indicating the presence of Gd3+inhances the energy transfer efficiency from host to Tb3+.4. In Ba3Gd(PO4)3:Eu3+, the energy transfer processes among Gd3+, Eu3+and O-Eu charge transfer state were investigated. Based on steady state spectra and decay curves of Ba3Gd(PO4)3:Eu3+, energy transfer from O-Eu charge transfer state to Gd3+was observed. There is also energy transfer from Gd3+6P7/2state to Eu3+; the transfer efficiency increases with Eu3+concentration. When Gd3+concentration is15mol%, the transfer efficiency is up to96.8%. The decaytime of Eu3+5Do state keeps-3ms with Eu3+concentration, indicating large quenching concentration of Eu3+in this host. |
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