The Preparation Of ZnAl₂O₄:Cr³⁺ Long Afterglow Phosphors And Their Performance

The long afterglow luminescent materials are widely used in night emergency instructions,optoelectronic device,home decoration,biotechnology and defense military because of their phosphorescence phenomenon after the radiation is removed.In the past decades,the study on the long afterglow materials has spread from the initial sulfide to the present aluminates and silicates doped by rare earth to obtain higher luminescence intensity and longer afterglow time.Moreover,with the emergency of new technologies,the preparation methods,luminescence types and energy excitation methods of long afterglow materials have increased obviously.In this paper,by using solid state reaction,we prepared the long afterglow materials of ZnAl₂O₄:Cr³⁺,whose performance was also investigated with XRD,PL and afterglow curves.Their luminescence and afterglow performance can be improved by co-doping technique.The main content of the thesis and results can be briefly summarized as following:?1?The ZnAl₂O₄:Cr³⁺,B³⁺ phosphors are prepared at different temperatures?1300?,1350? and 1400??by solid state reaction.By analyzing XRD,PL and the afterglow curves of ZnAl₂O₄:Cr³⁺,it can be found that the main phase of products is ZnAl₂O₄.Under the irradiation of UV light,emission spectrum of long afterglow materials is infrared spectrum.The increase of calcining temperature is in favor of crystallization of long afterglow materials and promotes luminescence centers to enter into ZnAl₂O₄ lattice to improve luminescence performance and increase afterglow intensity.In addition,there is a higher emission intensity under the irradiation of UV when the calcined sample is heated on 200? again,which indicates a mass of electrons are captured by deep traps in ZnAl₂O₄ host and heating promotes electrons in deep traps to be released rapidly??2?It is well known that the performance of phosphors can be improved by adding cosolvent.When H3BO3 is added,on the one hand,H3BO3 provides a liquid phase environment to makes luminescence center ions easy to enter into ZnAl₂O₄ lattice;on the other hand,since there is the radius difference between co-doping ions,the substitution of B³⁺ for Al³⁺ ions will cause the change of lattice environment,which would enhance luminescence and afterglow performance.In the study,the effect of different doped quantity of H₃BO₃ on fluorescence and afterglow performance were discussed in detail,and it is found that excess co-doped ions decrease its luminescence and afterglow performance.FInally,we find the optimum doping to promote luminescence and afterglow performance.?3?The influence of co-doped ions with different valence on the photoluminescence and phosphorescence of ZnAl₂O₄:Cr³⁺ were investigated by adding Na+,Mg2+,B³⁺ and Si4+ respectively.The experimental results revealed that co-doping ions would induce different effects:e.g.changing the local crystal environment around Cr³⁺ and producing oxygen vacancy,and influencing the frame structure due to the difference between M-O single bond strengths.These elements have different influence to the luminescence and afterglow performance.