Improvement On Long Afterglow Characteristics Of ZnGa2O4:Tb Nanophosphor Though Co-Doping Ce,Yions

Long afterglow materials are of a wide range of application prospects in many fields,such as indicator sign,solar energy utilization,biological image and so on because of their unique luminescent properties.So far,the existing long afterglow luminescent materials mainly belong to the aluminates and silicate systems,and the investigation about long afterglow luminescent properties of gallate material doped earth rare ions is relatively few.Considering the excellent material characteristics of gallate,therefore it is interesting work to optimize preparation technique of gallate doped earth rare ions,to explore the mechanism of the long afterglow material and to improve its luminescent properties.The main contents of this thesis are as follows:Three series of long afterglow phosphorescent nanophosphors including ZnGa₂O₄single-doped Tb³⁺,ZnGa₂O₄ co-doped 1.7Tb³⁺,yCe³⁺and ZnGa₂O₄ co-doped 1.7Tb³⁺,yY³⁺have been prepared by high temperature solid-state reaction.The crystal structure and surface morphology of some representative samples were characterized using XRD and SEM.The results show that the diffraction peaks of XRD belonging to the prepared ZnGa₂O₄ matrix are basically the same as those of the standard card,and there do not exist new diffraction peaks in the XRD diffraction patterns even though Tb³⁺,Ce³⁺and Y³⁺ions are implanted into the matrix,indicating that the ideal ZnGa₂O₄ matrix and ZnGa₂O₄:Tb³⁺,Ce³⁺/Y³⁺series long afterglow nanophosphors have been obtained successfully.It can be known from the SEM images that the most of particle morphology of ZnGa₂O₄ matrix are spherical,and the average particle size is about 50 nm.The particle morphologies of all nanophosphors still maintain spherical shapes after doping with Tb³⁺,Ce³⁺and Y³⁺ions,however,the particle sizes of different series samples present obvious change.Under the 280 nm ultraviolet excitation,there exist four main peaks in fluorescence spectra and afterglow spectra of three series of long afterglow nanophosphors and their center wavelengths are at 492,551,591and 625 nm which belong to f-f transition of Tb³⁺ion replacing Ga³⁺lattice within the octahedral coordination that is,they correspond to ⁵D₄-⁷F₅,⁵D₄-⁷F₄,⁵D₄-⁷F₃ and ⁵D₄-⁷F₂ of Tb³⁺ion,respectively,which also means that the active ion is still Tb³⁺ion even if a little cerium ions or yttrium ions are co-doped into ZnGa₂O₄.For fluorescence emission center of ZnGa₂O₄ nanophosphor single-doped Tb³⁺ion,the optimum concentration is 1.7 mol%.Speaking to ZnGa₂O₄ series samples co-doped 1.7Tb³⁺and yCe³⁺,when the concentration of cerium ion is 0.3 mol%,the photoluminescence is the most intense and its intensity is about 1.5 times that from the best sample Tb³⁺single-doped.Similarly,when the doping concentration of yttrium ion is 0.5 mol%,the fluorescence emission of ZnGa₂O₄ nanopowder co-doped Tb³⁺and Y³⁺ions is the most intense and its intensity is also about 1.5 times that from the best sample Tb³⁺single-doped.After 20 min excitation using ultraviolet light source,the measured afterglow time of the ZnGa₂O₄:1.7Tb³⁺long afterglow phosphor is about 140 min,and the visible time with the naked eye is about 200 min in dark room environment;The measured afterglow time of the ZnGa₂O₄:1.7Tb³⁺,0.5Ce³⁺sample is about 210 min,and its visible time with the naked eye is longer than 300 min in dark room environment,which are about 1.5 times than the corresponding times of the long afterglow material single-doped terbium;In addition,the measured afterglow time of the ZnGa₂O₄:1.7Tb³⁺,0.3Y³⁺sample is about 195 min,however,its visible time with the naked eye is also longer than 300 min in dark room environment.Therefore,co-doping of Ce³⁺or Y³⁺presents clear improvement on the properties of ZnGa₂O₄:Tb³⁺nanophosphors,not only on photoluminescence characteristics but also on long afterglow performance.The fitting results show that the decay curves of long afterglow obtained from three series of nanophosphors satisfy the double exponential equation.Finally,the mechanism of long afterglow emission is analyzed in detail based on the measurement data of thermoluminescence spectroscopy.