| Quantum cutting refers to the physical process that a fluorecent material emits two ormore lower energy photons after it absorbs one higher energy photon. During the process, thenumber of photons emitted is greater than the number absorbed. Theoretically, light emissionwith quantum efficiency greater than100%is feasible. In1999, Wegh et al reported the visiblequantum cutting under vacuum ultraviolet excitation of LiGdF4: Eu3+system on Science. Thequantum efficiency was195%. These studies provide theoretical foundation for the futuredesign and development of Mercury-free fluorescent lamps and plasma displays. With theupcoming energy crisis and severe environmental problem, there has been an urgent demandfor efficient photoelectric converters which can make a good use of solar radiation energy.Quantum cutting is of great potential for its possible application for that it might boost thephotoelectric conversion efficiency of solar cells. For this reason, rare-earth ion dopednear-infrared down-conversion materials is now a hot spot in research.This thesis has chosen vanadate as the host material for its great physical and chemicalstability. The luminescent characteristics of the rare-earth ion-doped vanadate phosphors areinvestigated. And the corresponding luminescent mechanisms of the down-conversion andenergy transfer are discussed.The research background of quantum cutting and the recent progress in the research ofnear-infrared quantum cutting materials are introduced. The meaning and content of thisresearch are discussed in Chapter1.In Chapter2, the typical energy transfer mechanism of inorganic luminescent materials isexplained. The phenomenon of concentration quenching and the reasons behind are introduced.The calculation of the energy transfer efficiency and the quantum efficiency is also discussed.Related theories about the synthesis and test of the samples are introduced. Raw materials andother equipments are listed.In Chapter3, Tm3+-doped and Tm3+/Yb3+codoped YVO4samples are synthesized byhigh-temperature solid-state method. The author investigates the three-photon luminescentcharacteristics in the near-infrared region under the sensitization of [VO4]3-ion group. Theauthor also studies the mechanism of the three-step continuous near-infrared three-photonquantum cutting, i.e.â‘ 1G4â†'3H4(1180nm);â‘¡3H4â†'3F4(1479nm);â‘¢3F4â†'3H6(1800nm), in which the3H4and3F4serves as the intermediate level.In chapter4，YVO4:2%Ho3+, x%Yb3+(x=0,1,3,6,10,20,30) phosphors are synthesized by high temperature solid state method. We investigated the luminescent properties and theprocess of the energy transfer between Ho3+and Yb3+ions. The corresponding mechanismmodel of the NIR down-conversion for Ho3+-Yb3+is build.In chapter5, the samples of GdVO4:1%Tm3+, x%Yb3+(x=0,1,5,10,20) and GdVO4:x%Yb3+(x=0,1,5,10,20,30) were synthesized and their luminescent properties were tested.The mechanisms of the energy transfer for the single-doped sample and co-doped sample arediscussed. And we testified the energy transfer from ultra violet excited [VO4]3-to Yb3+isdominant in the Tm3+and Yb3+codoped GdVO4. |
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