【作者】 段晓霞；

【导师】 黄世华；

【作者基本信息】 北京交通大学 ， 光学， 2009， 博士

【摘要】 长余辉磷光体在可见光很长的波段内有较强的吸收,它可以吸收太阳光而在暗处释放出可见光,所以长余辉在弱光照明方面得到了的利用,如果长余辉材料能广泛应用于生活对节能环保将非常有意义。目前长余辉发光机理的许多方面尚不明确,对于纳米长余辉的研究则更少。本论文在纳米尺度范围内对长余辉的相关特性展开研究,主要内容包括以下几个方面:1.分别用高温固相法和柠檬酸盐溶胶-凝胶自燃烧法制备了体相和形貌、粒径可控的SrAl₂O₄:Eu²⁺,Dy³⁺纳米长余辉磷光体。研究了溶胶的pH值、灼烧温度及柠檬酸用量对材料形貌、粒度及结晶性能的影响。全面考虑影响纳米颗粒制备的各种条件,控制溶胶的pH值在7,控制柠檬酸的用量为金属离子用量的2倍,在1000℃的高温下活性炭还原气氛中足以形成规整的纳米晶。2.利用溶胶-凝胶自燃烧法在900,1000,1100,1200℃下合成了粒径不同的纳米SrAl₂O₄:Eu²⁺,Dy³⁺长余辉磷光体。研究了纳米SrAl₂O₄:Eu²⁺,Dy³⁺的激发和发射光谱的特性,通过分析真空紫外激发光谱讨论了基质带隙随粒径的变化,继而利用热释光谱分析了纳米材料与体材料中深、浅陷阱的变化规律并讨论了引起这种变化的原因,结合对红外吸收光谱的分析,研究了表面吸附与表面态对发光强度及余辉衰减的影响;同时我们还深入研究了纳米材料和体材料的电流-电压特性;进一步分析了SrAl₂O₄:Eu²⁺,Dy³⁺长余辉的发光机理;另外,针对纳米长余辉磷光体存在的缺陷态,猝灭和易潮解等问题,用γAl₂O₃作壳层对纳米SrAl₂O₄:Eu²⁺,Dy³⁺进行表面修饰。通过对发光效率和能级寿命的分析讨论了表面修饰的理论和实验效果,实验证明,核-壳结构纳米颗粒的余辉特性并没有得到明显改善,这可能是由于包覆过程中引入了其他一些引起无辐射弛豫的因素,可以通过运用微乳液的方法使反应用水与被包覆样品有效隔离,或者通过引入过渡层改善晶格匹配情况。3.利用水热法在900,1000,和1200℃下合成了粒径不同的纳米SrS:Eu²⁺,Dy³⁺和SrS:Eu²⁺磷光体。结合SrS:Eu²⁺中的余辉动力学模型分析了SrS:Eu²⁺,Dy³⁺的发光和余辉特性,我们认为SrS:Eu²⁺,Dy³⁺中有深浅两种陷阱存在,深陷阱与Dy³⁺有关,而浅陷阱与S^2-空位有关;深陷阱对延长余辉有很重要的作用,浅陷阱对余辉强度有很大贡献;研究了样品的余辉衰减规律,对其根本原因作了深入的探讨。4.用水热法制备了一种SrAl₂O₄:Eu²⁺,Dy³⁺/SrS:Eu²⁺,Dy³⁺混合体系可变色长余辉磷光体。分析了水热处理在制备过程中的作用,讨论了此体系的发光和余辉特性。更多还原

【Abstract】 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.更多还原