| The long afterglow phosphorescence can be regarded as an optical phenomenon of great significance,which can continue to emit for several minutes,hours or even longer after the excitation is stopped.Long afterglow phosphors are special functional material,they can be used in night displays,security signs,optical storage medias,vivo bio-imaging and other special fields due to pollution-free,energy-saving and environmentally friendly.In recent years,related research on long afterglow luminescent materials has achieved a leap-forward development.However,there are still some problems in this research field such as ambiguity of afterglow mechanisms,monotony of emitting colors,limited afterglow time etc.At present,the aluminate material has the disadvantages of poor moisture resistance and emitting colors.Although the silicate has a stable structure,the luminescence intensity is much weaker than that of the aluminate system.Therefore,it is urgent to explore new long afterglow materials.In this thesis,the preparation of calcium stannate-based long afterglow luminescent materials was prepared by a high temperature solid state reaction method.The effects of preparation conditions on the properties of luminescent materials were studied.and the effect of Li+and R3+(R3+=B3+,Al3+and Ga3+)doping on the structure and luminescent properties of the materials was discussed.The main research contents and conclusions are as follows:(1)Preparation of Ca2SnO4:Tb3+long afterglow materials at different temperatures by high temperature solid state reaction method.By comparing XRD,PL and afterglow decay curves at different temperatures,it can be concluded that the optimum preparing temperature is 1400?.Then,a series of long afterglow materials doped with different concentrations of Tb3+ ions were also prepared by solid-state method at 1400?.The phase composition of the materials was also detected by XRD.Their luminescence spectrum and the afterglow decay curve were detected by PL.It was found that the luminescence intensity was the highest and the decay time was the longest when the concentration of Tb3+ was 0.100%,and the corresponding luminescence mechanism was also analyzed.(2)Long afterglow phosphors Ca2SnO4:Tb3+,Li+with a green light were successfully synthesized by solid-state reaction,and their phase composition and luminescent property also studied using X-ray powder diffraction(XRD),photoluminescence(PL)and afterglow decay measurement.The results show that adding a small amount of Li ions does not have a significant effect on the crystal structure of Ca2SnO4:Tb3+,and that Ca2SnO4:Tb3+,Li+samples are single phase of solid solutions.Their luminescent properties are strongly dependent on Li+ doping modes.The distortion of host lattice and change of the local crystal field symmetry around Tb3+ enhanced their emission intensity,while the formation of oxygen vacancy and the suitable depth traps improved their afterglow performance;but the association of Li i with V" ca,and excessive Li ions would worsen their phosphorescence.Their afterglow mechanism was proposed.(3)Ca2SnO4:Tb3+phosphors co-doped by R3+(R3+=B3+,Al3+and Ga3+)were successfully prepared by high temperature solid state reaction method.The results show that their luminescence can be effectively improved by co-doping R3+cations and adding Al3+ cation is superior to that with other two dopants whether in fluorescence or phosphorescence.The concentration quenching effect will weaken their luminescence beyond 0.07 when Al3+ cation is co-doped.The distortion of host lattice and change of local crystal field symmetry around Tb3+due to co-doping R3+can enhance their fluorescence.The formation and increase of oxygen vacancy(V..o)predominate in improving their phosphorescence,while the single bond strength of R-O also plays an important role. |
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