Synthesis And Electrooptical Characteristics Of Nanoscale And Bulk Long Persistent Phosphors

Long persistent phosphor has a strong absorption in the visible region.It absorbs sunlight and releases the energy in the darkness.These days,it is commonly used as weak light source.In fact,many researchers focus on this environment protecting and energy saving material in order to make full use its advantages in daily life.However,many aspects of the mechanism for long afterglow still remain unclear. Nanoscale long persistent phosphor is seldom studied recently.In this dissertation, nanoscale long persistent phosphors were studied.The important contents are as follow:1.Bulk long persistent phosphor SrAl₂O₄:Eu²⁺,Dy³⁺was prepared by high temperature solid state method.Shape and size dependent nanoscale ones were prepared by auto-combustion of citrate gelatin.The pH value,sintering temperature and quantity of citric acid used in the process of material preparing have effect on the shape,size and crystallinity,which were discussed respectively.Considering all the aspects,shape ruled nanoparticles were prepared at 900-1200℃in active carbon atmosphere by controlling pH at 7,quantity of citric acid as two times of all the metal cations.2.Nanoscale SrAl₂O₄:Eu²⁺,Dy³⁺long persistent phosphors with diferrent size were prepared by auto-combustion of citrate gelatin at 900,1000,1100 and 1200℃.The excitation and the emission spectra were studied.Quantum size effect of nanoscaled SrAl₂O₄ changed the bandgap,which was discussed by using VUV exciting spectra. Afterwards,the existing or not of deep or shallow traps in nanoscale and bulk SrAl₂O₄: Eu²⁺,Dy³⁺was deeply analyzed by using thermoluminescence spectra.The emission intensity and afterglow decay were discussed by using FTIR spectra.The I-V character of bulk and nanoscale SrAl₂O₄:Eu²⁺,Dy³⁺was deeply studied.The mechanism of long persistent phosphorescence was analyzed furtherly.Additionally,in view of phosphorescence quenching resulted by surface state and the instability resulted by air slaking,we selectedγAl₂O₃ as shell layer to wrap the SrAl₂O₄:Eu²⁺,Dy³⁺nanoparticle. The effects of theoretical and the experimental surface modification were discussed respectively by using luminous efficiency and decay curves.It was found that this core-shell structure only increase the water resistance but can not improve the afterglow decay or decrease fluorescent quenching because other irradiative relaxiation was caused in the process of surface amending.The other amending route and transition layer can be used to avoid water for chemical reaction and improve the lattice match.3.Nanoscale SrS:Eu²⁺,Dy³⁺and SrS:Eu²⁺was prepared at different temperature by hydrothermal method.The optical and persistent properties were analyzed by using the dynamic model of long persistent phosphorescence in SrS:Eu²⁺.We think that two kinds of traps exist in SrS:Eu²⁺,Dy³⁺,which are the deep traps and the shallow ones. The deep traps have something to do with Dy³⁺and the shallow traps have something to do with S^2-vacancies;the former is very important for prolong decay time and the latter decide the afterglow intensity.Moreover,the afterglow decay of different samples and the reason for different decay were discussed deeply.4.A mixed system of SrAl_O4:Eu²⁺,Dy³⁺SrS:Eu²⁺,Dy³⁺was prepared by hydrothermal method.Hydrothermal treatment is helpful for separating the two phases out from the hot liquid,which was discussed.The optical characteristics were analyzed deeply.