【作者】 蒙延双；

【导师】 谢刚；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2007， 博士

【摘要】 针对光电子信息领域的几种球形稀土掺杂荧光体材料，发展了一种利用纳米拟薄水铝石胶粒特性的多尺度复合溶胶体系的雾化-灼烧制备荧光材料的技术路线。采用含纳米胶粒的拟薄水铝石胶体和二氧化硅纳米粉体作为铝源和硅源，配合硝酸锶、硝酸铕、硝酸镝等形成复合胶体，采用雾化—灼烧技术制备了Al₂O₃：Eu³⁺、SrAl₂O₄：Eu²⁺，Dy³⁺、Sr₂Al₂SiO₇：Eu³⁺及Sr₂Al₂SiO₇：Eu²⁺荧光材料。从原子结构、纳米、微米多尺度层次上，分析离子、纳米晶粒、纳米胶粒自组装分级结构球形荧光颗粒的形成机理。将雾化过程工艺参数关联荧光体微结构和光谱性能，以实现荧光颗粒粒径、形貌和发光性能的可调控。取得如下主要成果：1．解析了胶溶后的纳米拟薄水铝石胶粒的细微结构。XRD和场发射透射电镜分析结果显示，拟薄水铝石原料是由纳米AlOOH晶粒组成的多晶粉末。加入HNO₃作为胶溶剂，调节pH=2.0得到胶粒大小～30nm的稳定胶体。提出拟薄水铝石胶溶机理为：胶溶剂HNO₃与部分拟薄水铝石纳米晶粒表面发生化学反应，未反应的纳米晶粒作为胶核并带正电，胶核吸附溶剂中的NO₃^-离子形成双电层，增大胶粒间的空间位阻，从而获得稳定的拟薄水铝石胶体。2．研究并提出了溶液和拟薄水铝石胶体作为喷雾前驱体，获得亚微米球形干燥颗粒的形成机理和模型。研究发现溶液干燥结晶过程符合均相成核机理；拟薄水铝石胶体干燥过程中，胶粒作为晶种，胶体干燥过程符合非均相成核机理。拟薄水铝石纳米胶粒本身由纳米尺度AlOOH晶粒组成，纳米胶粒间再因范德华力、毛细管力等自发聚集，形成具有分级结构的球形拟薄水铝石干凝胶颗粒。3．解析了纳米拟薄水铝石胶粒与稀土铕离子之间形成的稀土复合胶体的粒子行为，考察得到凝胶化后形成的纳米／微米颗粒的分级结构规律。研究发现Eu³⁺离子在拟薄水铝石胶粒表面的吸附为自组装过程。Eu³⁺离子在静电引力作用下，自发地在拟薄水铝石胶核表面发生化学吸附形成正电性胶核。Eu³⁺离子发射光谱特征研究表明Eu³⁺离子在拟薄水铝石胶粒表面的吸附密度D（mol／m²）决定于AlOOH与Eu³⁺物质的量之比。正电性胶核吸附溶剂中的NO₃^-离子形成胶粒，再由胶粒自组装形成三维分级结构的AlOOH／Eu（NO₃）₃干凝胶颗粒。AlOOH／Eu（NO₃）₃干凝胶颗粒经高温灼烧获得球形三维梯次结构Al₂O₃：Eu³⁺荧光颗粒。研究了激活剂Eu³⁺离子对AlOOH高温相变的影响，XRD和热分析结果表明，在AlOOH中掺杂2％（摩尔比）Eu³⁺离子使γ-Al₂O₃→θ-Al₂O₃相变温度从882℃升高到1054℃，θ-Al₂O₃→α-Al₂O₃相变温度从1224℃升高到1237℃。升高的原因是：一方面，晶格常数计算结果表明Eu³⁺在γ-Al₂O₃和θ-Al₂O₃基质中部分取代Al³⁺离子，阻碍了Al³⁺离子扩散，使基质晶粒生长速度减小：另一方面由于θ-Al₂O₃→α-Al₂O₃相变时生成少量化合物EuAl₁₂O₁₉，EuAl₁₂O₁₉在晶界间存在，阻碍相变过程的Al³⁺离子扩散。对Al₂O₃：Eu³⁺荧光体的发光性能做了分析。结果显示，γ-Al₂O₃和θ-Al₂O₃基质中Eu³⁺离子⁵D₀→⁷F₂跃迁对应的发射峰位于617nm，与大晶粒Eu₂O₃中Eu³⁺离子⁵D₀→⁷F₂跃迁发射（612nm）相比红移5nm。4．用拟薄水铝石复合溶胶喷雾-灼烧方法制备了不需研磨的SrAl₂O₄：Eu²⁺，Dy³⁺长余辉荧光颗粒。与固相法相比，喷雾干燥法具有低温烧成、形貌粒度可控的特点。添加少量H₃PO₄作为助熔剂，采用喷雾干燥工艺1200℃灼烧得到不需研磨的直径～5μm的球形SrAl₂O₄：Eu²⁺_0.02，Dy³⁺_0.04长余辉荧光颗粒。该荧光体发射主峰位于516nm，陷阱深度为0.589eV。5．首次采用纳米拟薄水铝石胶粒、纳米氧化硅和稀土硝酸盐形成复合溶胶，制备并研究了铕离子掺杂的Sr₂Al₂SiO₇荧光体，对荧光体微结构及其光谱进行了解析。以Sr₂Al₂SiO₇作为荧光体基质目前没有文献报道。研究了基质Sr₂Al₂SiO₇的形成过程机理。提出了干凝胶颗粒中组分AlOOH、SiO₂和Sr（NO₃）₂间的反应机理为：灼烧过程首先发生AlOOH和Sr（NO₃）₂的分解反应，并生成SrAl₂O₄和Sr₂SiO₄，SrAl₂O₄与Sr₂SiO₄从1000℃开始相互反应生成Sr₂Al₂SiO₇，至1200℃完全反应得到Sr₂Al₂SiO₇纯相。6．研究了不同灼烧温度制备的Sr₂Al₂SiO₇：Eu³⁺荧光体的发光性能和机理。Sr₂Al₂SiO₇：Eu³⁺荧光体的578nm，593nm，613nm三个发射峰，分别来自Eu³⁺离子从基态⁵D₀到⁷F₀，⁷F₁，⁷F₂的跃迁。提出了将⁵D₀→⁷F₂的相对发射强度与⁵D₀→⁷F₁的发射强度的比值k作为研究Sr₂Al₂SiO₇基质对称性的依据，从1000℃开始到1400℃随着灼烧温度的升高，k值增大，说明基质晶体对称性随灼烧温度的升高而增强。7．对Sr₂Al₂SiO₇：Eu²⁺荧光体发光性能和发光机理进行了分析。XRD分析及晶体常数结果表明，Eu²⁺离子取代Sr²⁺离子进入基质Sr₂Al₂SiO₇的晶格，形成取代固溶体。其激发谱主要由峰值位于326nm附近的带构成，属于Eu²⁺的4f→5d跃迁吸收带。发射光谱峰值波长位于～500nm，属于典型的Eu²⁺离子4f⁶5d¹到4f⁷组态间跃迁导致的宽带发射。研究了Mg²⁺、Ca²⁺、Ba²⁺阳离子部分取代基质Sr₂Al₂SiO₇中的Sr²⁺离子对Sr₂Al₂SiO₇基质微结构和Sr₂Al₂SiO₇：Eu²⁺荧光体发光性能的影响。结果表明，由于Mg²⁺、Ca²⁺离子部分取代半径比它大的Sr²⁺离子导致基质晶体场强度减弱，Eu²⁺的5d能级劈裂减小，Eu²⁺离子的最低4f⁶5d态移向高能，导致Eu²⁺离子发射峰主峰分别蓝移至470nm和496nm。Ba²⁺离子电负性和离子半径比Sr²⁺离子大，取代Sr₂Al₂SiO₇中Sr²⁺离子后，处在其周围的Eu²⁺离子外层电子受Ba²⁺离子影响，电子云膨胀；同时，掺入Ba²⁺离子后Sr₂Al₂SiO₇晶场强度增强，晶场对Eu²⁺离子5d能级的劈裂程度增大，发射峰红移至520hm。通过阳离子掺杂实现Sr₂Al₂SiO₇：Eu²⁺荧光体发射光谱可调，对多基色配色实现白光发射具有重要的意义。更多还原

【Abstract】 A two-step of Spraying and Sintering of Pseudoboehmite Composite Sol （SSPCS） technique was developed to fabricate several hierarchical sphere-like phosphors for optoeletronic field. Stable pseudoboehmite composite sol was obtained using pseudoboehmite sol as dispersant, with the addition of SiO₂, Sr（NO₃） ₂, Eu（NO₃） ₃ and Dy（NO₃） ₃．The self-assembly mechanisms of ions, nanocrystals and colloidal nanoparticles consisted in the composite sol were analyzed on multi-scales of atom, nanometer and micrometer. Phosphors of Al₂O₃:Eu³⁺, SrAl₂O₄:Eu²⁺,Dy³⁺, Sr₂Al₂SiO₇:Eu³⁺ and Sr₂Al₂SiO₇:Eu²⁺ were prepared by the SSPCS technique. The granularity and morphology of the phosphors can be controlled by changing the composite sol concentration and the spraying parameters. The influences of microstructures on the photoluminescence characteristics of the phosphors were analyzed. The main results as following:1．The microstructures of pseudoboehmite colloidal particles were investigated. XRD and Field Emission Transmission Electron Microscope （FETEM） results show that pseudoboehmite powder is composed of AlOOH nanocrystals. Stable pseudoboehmite sol was obtained by adding HNO₃ as peptizing agent and adjusting pH=2．0．The peptizing mechanism was presented. HNO₃ react with AlOOH at the interfaces of AlOOH nanocrystals. The AlOOH nanocrystals were electropositive when pH=2．0 adjusted by HNO₃．Negative NO₃^-ions were then adsorbed on the AlOOH nanocrystal surface and formed electronic double layer. TEM result shows that the AlOOH colloidal particle size is～30nm.2．The crystallization mechanism for pseudoboehmite sol was different from that for nitrate solution during the spray-drying process. The crystallization of nitrate solution during spray-drying process is presumed fitting homogeneous nucleation mechanism. However, as for pseudoboehmite sol, colloidal AlOOH nanoparticles act as crystallization centres. The crystallization of pseudoboehmite sol agrees with a heterogeneous nucleation mechanism. Colloidal AlOOH nanoparticles agglomerated under van der waals and capillary forces and formed hierarchical sphere dry AlOOH gel particles in the spray-drying process.3．The interaction of Eu³⁺ ions and colloidal AlOOH nanoparticle was investigated. The self-assembly of Eu³⁺ ions on the surface of AlOOH nanocrystal was attributed to the chemical adsorption caused by electrostatic attraction. Electropositive colloidal nucleus AlOOH/Eu³⁺ were consequently formed. The photoluminescence characters of Eu in AlOOH/Eu（NO₃） ₃ composite sol system show that the adsorption density of Eu³⁺ ions on colloidal AlOOH nucleus is determined by the mol ratio of Eu³⁺ to AlOOH. AlOOH/Eu（NO₃） ₃ colloidal particles were composed of AlOOH/Eu³⁺ nucleus and NO₃^-electronic double layer. Three-dimensional hierarchical sphere dry AlOOH/Eu（NO₃） ₃ gel particles were prepared by spray-drying technique, using AlOOH/Eu（NO₃） ₃ composite sol as precursor.Hierarchical Al₂O₃:Eu³⁺ phosphor particles were obtained by sintering dry AlOOH/Eu（NO₃） ₃ gel particle at a temperature range of 600～1000℃. The effect of dopant Eu³⁺ ion on the phase transformation of AlOOH was investigated. XRD and DSC results indicated that the phase transformation temperatures ofγ-Al₂O₃→θ-Al₂O₃ andθ-Al₂O₃→α-Al₂O₃ were increased from 882℃to 1054℃and 1224℃to 1237℃, respectively, by doping 2%（mol） Eu³⁺ ion. The calculated lattice constants results indicate that Eu³⁺ ions partial substitute Al³⁺ ions inγ-Al₂O₃ andθ-Al₂O₃ lattices. The crystal growth ofγ-Al₂O₃ andθ-Al₂O₃ phases is hindered by the Eu³⁺ ions. A newly formed compound EuAl₁₂ O₁₉ was detected by XRD. The compound EuAl₁₂ O₁₉ possibly resultes in the increase of theθ-Al₂O₃→α-Al₂O₃ phase transformation temperature.The photoluminescence spectra of Al₂O₃:Eu³⁺ phosphor was detected. The emission of 578nm, 588nm（593nm） and 616nm are attributed to the transition from ⁵D₀ to ⁷F₀, ⁷F₁ and ⁷F₂ in Eu³⁺ ions of Al₂O₃:Eu³⁺ phosphor, respectively. The emission of ⁵D₀→⁷F₂ transition lies at 617 nm, which is same to the emission of Eu³⁺ ion inα-Al₂O₃:Eu³⁺ nanoparticle and has a red shift of 5nm compared with the emission of Eu³⁺ ion in bulk Eu₂O₃． 4．Spheric SrAl₂O₄:Eu²⁺_0．02 ,Dy³⁺_0．04 afterglow phosphor was prepared by the SSPCS technique, with addition of a small amount of H₃PO₄ as flux. The SrAl₂O₄:Eu²⁺_0．02 ,Dy³⁺_0．04 phosphor particles were unnecessary of further ball-grinding and with a mean particle size of～5μm. The spectra study indicated that the emission spectra of the SrAl₂O₄:Eu²⁺_0．02 ,Dy³⁺_0．04 phosphor was a broad band spectra peaking at 516 nm. The trap depth of the SrAl₂O₄:Eu²⁺_0．02 ,Dy³⁺_0．04 phosphor was calculated to be 0．589eV.5．Substrate Sr₂Al₂SiO₇ and phosphors Sr₂Al₂SiO₇:Eu³⁺ and Sr₂Al₂SiO₇: Eu²⁺ were prepared by the SSPCS technique. The reaction mechanism for synthesization of substrate Sr₂Al₂SiO₇ was investigated. The dry gel particles were consisted of AlOOH, SiO₂ and Sr（NO₃） ₂．On heating, the components AlOOH and Sr（NO₃） ₂ decomposed and reacted with each other. Two compounds SrAl₂O₄ and Sr₂SiO₄ were synthesized when the sintering temperature was below 1000℃. XRD results showed that pure Sr₂Al₂SiO₇ compound was composed when the sintering temperature was above 1200℃.6．The photoluminescence characteristics and mechanisms of the Sr₂Al₂SiO₇:Eu³⁺ phosphors obtained with different sintering temperatures were examined. The emission of 578nm, 593nm and 616nm are attributed to the transition from ⁵D₀ to ⁷F₀, ⁷F₁ and ⁷F₂ in Eu³⁺ ions of Sr₂Al₂SiO₇:Eu³⁺ phosphor, respectively. The ratio of intensity of 613nm peak to that of 578nm peak was defined as k. The value of k increased with the increasing of sintering temperature from 1000℃to 1400℃. It indicates that the crystal symmetry of substrate Sr₂Al₂SiO₇ enhances with the increasing of sintering temperature.7．The photoluminescence characteristic and mechanism of the Sr₂Al₂SiO₇:Eu²⁺ phosphor was detected. XRD result and the calculated lattice constant indicate that the Eu³⁺ ions partial substitute on Sr²⁺ sites in Sr₂Al₂SiO₇ lattice. The emission peak centered at 500nm observed in the Sr₂Al₂SiO₇: Eu²⁺ phosphor was considered arise from the transition of 4f⁶ 5d¹→4f⁷ in Eu²⁺ cation.The substitution mechanisms of Mg²⁺ ,Ca²⁺ and Ba²⁺ ions for Sr²⁺ in Sr₂Al₂SiO₇ lattice were respectively discussed. The effects of the substitutions on the microstructures and the photoluminescence characteristics of Sr₂Al₂SiO₇:Eu²⁺phosphors were researched. It indicates that the crystal field intensity of Sr₂Al₂SiO₇ decreases when the Sr²⁺ site is substituted with Mg²⁺ or Ca²⁺ ion. which size are smaller than that of Sr²⁺ ion. The split of 5d energy level of Eu²⁺ decreases and the emission spectra of peak Sr₂Al₂SiO₇:Eu²⁺ phosphor blue shifts to 470nm or 496nm when substitute Sr²⁺ with Mg²⁺ or Ca²⁺ ions。On the contrary, for larger ion, the substitution of Ba²⁺ for Sr²⁺ results in increasing of the crystal field intensity of Sr₂Al₂SiO₇．The split of 5d energy level of Eu²⁺ increases. The emission spectra of Sr₂Al₂SiO₇:Eu²⁺ phosphor shift to 520nm.更多还原