Studies On Spectroscopic Characterization And Energy Transfer Mechanism Of Fluoride Crystals Doped With Rare Earth Ions

The research content of this thesis consists of two parts:the luminescent proper-ties of rare earth ions doped fluoride materials, which is presented in chapter2-5, and the luminescent properties of Tb3+doped Lu3Al5O12film prepared by Pechini sol-gel process as well as dip-coating technique, which is discussed in chapter6.In chapter1, a brief introduction of research background and summary of the mech-anisms of lanthanide luminescent materials, the most useful qualitative theorectionl methods and the current and potential applications of these materials are made.In the research part of fluoride materials, the mechanism of quantum cutting and upconversion are summerized in chapter2. Then, from chapter3to chapter5, the lu-minescent properties of rare earth ions doped CsGd2F7, K2GdF5and LiKGdF5crystals under VUV and UV excitations are presented in detail. In addition, the upconversion luminescence process of CsGd2F7:Er3+, Dy3+under980nm excitation was also re-ported and interpreted in chapter3. The research contents and conclusions are listed below:1. The excition spectra in VUV and UV range and VUV and UV excited emis-sion spectra of CsGd2F7:Er3+, Dy3+were measured. The main transitions of emis-sion spectra are designated by using Dieke diagram associated with analyzing the ki-netic process of luminescence. The energy of the lowest4f-5d absorption and charge transfer state of rare earth ions doped in CsGd2F7were calculated by using empirical formulae, and the calculated results of the lowest4f-5d absorption of Er3+and Dy3+are well agreed with the experimental results. For the1at.%Er3+and0.2at.%Dy3+co-doping concentration, the quantum cutting phenomenon following the corss relaxation energy transfer from Er3+to Gd3+are observed. The upconversion green-light emis-sion of CsGd2F7:Er3+, Dy3+under980nm excitation was observed, we ascribe the upconversion mechanism to be excited state absorption. Finally, the CIE coordinates of the emission spectra of CsGd2F7:Er3+, Dy3+under various excitation wavelength were calculated. It is shown that the white light emission can be achieved by slightly enhancing emission of blue light.2. The excition spectra in VUV/UV range and VUV/UV excited emission spectra of K2GdF5were measured. The variation of intensity ratio between5D4→7FJ and5D3→7FJ under various excitation is observed. It is suggested that the variation is due to the partial aggregation of Tb3+in K2GdF7crystal, which makes the cross relaxation between Tb3+ions more efficient. The cross relaxation energy transfer between two Tb3+ions was identified to be ED-ED mechanism.3. Detailed analysis of excitation and emission spectra of Er3+(2at.%) and Sm3+(0.4at.%), Er3+(1at.%)and Dy3+(0.2at.%),Tm3+(l at.%)and Dy3+(0.2at.%)co-doped LiKGdF5was made, and their potential as quantum cutting materials was investigated, meanwhile, the energy transfer mechanism under different excitation was explored.In the second part, the basic principles and characteristic of sol-gel method were given. Besides, Lu3Al5O12(LuAG) thin films with different Tb3+concentration were prepared on carefully cleaned (111) silicon wafer by the Pechini process and dip coating technique followed by heat treatment performed in the temperature range from800to1100℃. The crystal structure was analyzed by XRD. The results show that LuAG film starts to crystallize at about900℃, and the particle size increases with the sintering temperature. Excitation and emission spectra of Tb3+doped LuAG films were mea-sured. The effects of heat-treatment temperature and doping concentration of Tb3+on the luminescent properties were also investigated. For a comparison study, Tb3+-doped LuAG powders were prepared by the same sol-gel method.