| The Rare Earth (RE) doped up-conversion (UC) glassy materials exhibit considerable potential applications in infrared detection, three-dimension volumetric display, short wave solid-state lasers, color display, and white-light illumination and so on. In a previous work, the fluoride glasses were widely studied for low phonon energy and high up-conversion efficiency. However, they were difficult for wide application for their less favorable chemical and mechanical stability. The oxides are of high transparency, chemical and thermal stability, but their high phonon energies limited their practical application. Thus, it will be a hot spot in this field for novel hosts that produce high up-conversion efficiencies and excellent chemical durability or thermal stability. Two major methods were used to enhance the up-conversion efficiency. One method, co-dope with a variety of rare earth ions. The efficiency that was observed for this up-conversion process was low in singly doped media, but it would be more efficient by using Yb3+ ions as sensitizer ions. The other method, select low phonon-energy host glass. The glasses converted into glass-ceramics after heat treatment at suitable temperature and the up-conversion efficiency was promoted dramatically. Therefore, oxyfluoride transparent glass-ceramics co-doped with RE ions attracted researchers great interests, since they exhibited high luminescent efficiency, high transparency, chemical stability and excellent up-conversion behaviors. That assure their potential application in the field such as solid lasers, optoelectronic communication devices and high density memories.In this experiment, the influence of Yb3+ ions concentration on up-conversion efficiency was studied. The up-conversion efficiency was dramatically improved by addition Yb3+ ions into Tb3+ ions and Tm3+ ions. By adjusting the concentration of Yb3+,Tb3+ ions or the excitation power can result in large color adjustability. The energy transfer processes between Tb3+, Tm3+ and Yb3+ ions and possible up-conversion mechanisms were discussed. The luminescence properties of glass-ceramics were also studied, compared with the precursor glass, the glass-ceramic luminescence intensity increased significantly. The efficiency of up-conversion luminescence was improved, and the reasons for the enhancement of luminescence were analyzed.The exordium introduced the mechanism of up-conversion process and outlined the research method and its application and several factors affecting on up-conversion efficiency. Then proposed the problem-how to improve the up-conversion efficiency. The glass-ceramics can effectively improve the up-conversion efficiency with perfect chemical stability and mechanical properties. At last, the purpose and significance of researching Tb3+, Tm3+ and Yb3+ co-doped oxyfluoride glass-ceramic system was described.In Chapter 2, an introduction of preparation and characterization for oxyfluoride glass and glass-ceramics. The experimental method consisted of specification of materials, sample preparation and spectra measurement in detail.In Chapter 3, the effects of Yb3+ions concentration on the emission intensity of Tb3+ ions and Tm3+ ions were investigated. As co-doped Yb3+ ions, the luminescence were dramatically enhanced, which indicated the important role of Yb3+ ions in energy transfer. The concentrations of Tb3+ ions and LD pump power effecting on up-conversion luminescence properties were studied. By adjust the concentrations of Yb3+ ions, Tb3+ ions and the LD pump power, it could provide a wide color gamut tunable. When the Tb3+ ions concentration was 0.1mol%, the white light was observed. With increasing excitation power, the enhancement of the intensity ratioes of red-green-blue were varied. Compared two-phone absorption process with three-photon absorption process of the blue emission, the latter intensities increase faster. According to the relation between the up-conversion intensities and the power pump, the up-conversion luminescence of the short wave Tb3+ ions were three-photon absorption up-conversion process, the long wave of Tb3+ ions were two-photon absorption up-conversion process; the Tm3+ ions blue up-conversion luminescence at 476 nm was three-photon absorption up-conversion process, the red emission at 655 nm was two-photon absorption up-conversion process. This material could be used as color tunable visible lasers or color display materials, at the same time bring a new white-light illumination material.In Chapter 4, Tb3+-Tm3+-Yb3+doped CaF2/SrF2 oxyfluoride glass-ceramics were prepared and the luminescence behaviors were studied. The up-conversion luminescence intensities of SAC-TbTmYb and SAS-TbTmYb glass-ceramics were much stronger than that in the glasses, the reasons were explained and the possible up-conversion mechanisms were discussed. Meanwhile, the microstuctures of the SAC-TbTmYb and SAS-TbTmYb glass-ceramics were observed by TEM. TEM image show that the size of precipitated crystals CaF2 were around 20 nm at heat treating 720℃and the size of precipitated crystals SrF2 were around 10 nm by heat treating at 700℃. The results agreed well with the calculation of XRD. In this study, the local vibration environment around rare earth in the glass-ceramic was examined with the use of Eu3+.In Chapter 5, main research results were summarized and the existed problems and further research direction were pointed out. |
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