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Studies On The Relationship Between Micro-structure And Luminescence Properties Of Sr2MgSi2O7:Eu2+,Dy3+

Posted on:2017-03-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:O HaiFull Text:PDF
GTID:1361330566452801Subject:Materials science
Abstract/Summary:PDF Full Text Request
Long-lasting luminescent material is one kind of energy-saving material which can continuously shine under no light environment after illuminated.Thus it is an energy saving and environmental protection material.Recently,new long-lasting luminescent materials are mainly silicate and aluminate luminescent material,due to the water resistance of silicate material,this paper adopted silicate long-lasting luminescent materials Sr2MgSi2O7:Eu2+,Dy3+as research object.The research on this material has been carried out only for last ten years which still remains many questions to explore.In long-lasting luminescent material,traps are essential to the afterglow property.In substrate,defects act as the trap while the micro-structure can be observed to understand the change of traps.Therefore,this paper will focus on material's micro structure and research the relationship between micro-structure and luminescence properties.The research content and result are as following:The effect of grain surface of Sr2MgSi2O7:Eu2+,Dy3+long-lasting luminescent material on luminescent properties were researched systematically.The material was crushed by ball milling,roller milling and artificial agate mortar grinding.The testing results indicated that roller milling kept the grain integrity with most shallow trap depth and biggest trap density,which led to the best luminescence properties;but ball milling destroyed the integrity of grain which produced more new surfaces with deepest trap depth and smallest trap density,which led to the worst luminescence properties;Artificial grinding only destroyed part of the surfaces with intermediate trap depth and luminescence properties.The elemental analysis indicated that grain surfaces obtained under reducing atmosphere have more oxygen vacancy which would give a great increase to the luminescence properties if coupled with proper trap depth and density.The new surfaces by crushing were reduced again and the result indicated that:when the new surfaces with secondary reduction owned increased luminescent properties,shallower trap depth and greater density;when the luminous powder obtained through roller milling reduced again,the concentration of oxygen vacancy quenched with the grain surfaces reduced again.Above results demonstrated the important role of oxygen vacancy and its density to the luminescence properties.As the samples oxidized again,the luminescence properties decreased significantly.The luminous powder used under common temperature should use roller milling while under high temperature reduction condition suitable for ball milling.Meanwhile,with the increasing specific surface area of Sr2MgSi2O7:Eu2+,Dy3+luminous powder,the grain boundaries and whole grains broke successively and the luminescence properties gradually decreased.The possible application of mechanical luminescence of long-lasting luminescent material Sr2MgSi2O7:Eu2+,Dy3+was discussed through its mechanical luminescence properties.The result showed that the mechanical luminescence intensity increased with the increasing pressure on samples;the development of this material in mechanical luminescence field is limited duo to the isotropic structure easily damaged after mechanical luminescence.The effect of grain characteristics on the types,trap depth and density as well as luminescence properties of defects were researched through changing the sintering schedule.The results illustrated that calcination temperature gave a high influence to the luminescence properties which mainly by changing the grain size and defect types in them.With the increasing sintering temperature,the grain crystallinity rose higher and more obviously,the grain size increased and specific surface area reduced,thus the surface with enriched defects and shallow traps reduced,the trap depth enlarged as well.When the sintering temperature is 1240?,the excitation and emission spectra of luminous powder as well as intensity of initial brightness were the highest;When the holding time increased,the grain crystallinity rose higher and more obviously,however hold temperature had little influence on the trap depth,when the holding time reachs 2h,the trap density is biggest,with the reducing time increased,the effective trap density increasingly decreasing which greatly reduced the intensity of emitted light and afterglow brightness;further more,whit the decrease of cooling rate,the crystallinity of grain became more complete and grain crystallinity rose higher and more obviously,when the cooling rate was 3?/min,the crystallinity was in a intermediate status which provided suitable trap and the luminescent properties of this luminous powder significantly better than other samples.Spherical,bacilliform and porous Sr2MgSi2O7:Eu2+,Dy3+long-lasting luminescent material were prepared through different wet-chemistry methods and carried out comparison to the luminous powder with same meshes obtained by high temperature solid state reaction.Although all of the luminescent properties through wet-chemistry methods were slight lower than the one of high temperature solid state reaction,they had advantages of without pulverizing,uniform distribution,etc.The emission spectrum of luminous powder prepared through wet-chemistry methods blue shifted which was caused by the crystal field changing located in luminescence center Eu2+.Eu ions single-doped Sr2MgSi2O7:Eu2+show some certain luminous performance.In Sr2MgSi2O7:Eu2+,Dy3+material,Eu2+ions not only could act as the luminescence center but also influenced the trap depth and density introduced by Dy,in which the Dy ions only act as traps.A new luminescence model was proposed combined with above mentioned results:after the luminescence center Eu2+was excited,the free electrons and holes were captured by congeries(VO··VSr??EuSr)n or(2DySr·VSr??EuSr)n,when n was in proper scope,it was favorable for the increasing of initial brightness.It was favorable for increasing the afterglow time after the oxygen ion vacancy VO··?DySr·and cation vacancy VSr??were captured.The former acted as shallow trap while the latter acted as deep trap.
Keywords/Search Tags:Sr2MgSi2O7:Eu2+,Dy3+, Long-lasting luminescent material, micro-structure, trap, luminescent properties
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