【作者】 徐玲玲；

【导师】 张治国；

【作者基本信息】 哈尔滨工业大学 ， 光学， 2008， 博士

【摘要】 自1964年发现Y₂O₃:Eu是一种高效红色荧光粉以来,稀土发光材料经历近45年的迅猛发展,己成为信息显示、照明光源、光电器件等领域的支撑材料,为社会发展和技术进步发挥着日益重要的作用。显示技术的发展向着高清晰、数字化、平板化的发展方向逐步迈进,对稀土发光材料的开发和改进也提出了新的要求。另外,大功率红外半导体激光器的成熟为上转换显示器的研发开拓了新的契机,因此,对上转换荧光粉的性能研究将加速上转换显示的实际应用。本文提出利用蔗糖燃烧法合成纳米荧光粉,研究合成机理及影响产物表面形貌、发光性能的因素。以显示、照明用荧光粉为研究对象,在合成方法、上转换荧光增强、荧光粉包覆及颜色调控等方面进行了实验研究和理论论证。首次采用蔗糖燃烧法合成纳米级Y₂O₃:Eu和Gd₂O₃:Eu荧光粉,研究了蔗糖络合机理和实验条件对粉体表面形貌和发光性能的影响。蔗糖燃烧法降低了荧光粉的成相温度;燃烧过程中产生的热量和气体之间存在竞争关系,影响样品表面形貌和发光性能;实验结果表明后处理温度高,蔗糖浓度大能够减少荧光粉处于表面态的Eu³⁺。蔗糖燃烧法还可以制备其他发光材料,是一种能够广泛推广的低廉的发光材料合成方法。考察基质材料结构的对称性降低引起的上转换发光增强。对具有低对称性结构的单斜相Gd₂O₃:Er荧光粉的Stokes发光及上转换荧光强度与掺杂浓度的依赖关系及发光机制做了详细的讨论。研究发现,上转换荧光强度随掺杂浓度的增加而增强;与立方相Gd₂O₃:Er荧光粉的对比研究发现,单斜相较立方相可提供更多的掺杂格位,增强了离子间能量传递几率,有利于增强上转换发光;速率方程推到结果证实了相邻Er³⁺间的能量传递4I11/2+4I11/2→4F9/2+4I13/2是红光和蓝光增强的主要原因。实验结果及理论论证认为单斜相较立方相更有利于增强上转换发光。以掺杂的形式向基质晶格中引入杂质离子或敏化剂实现荧光增强。对Gd₂O₃:Zn,Er多晶粉末的结构和Stokes发光及上转换发光性质研究表明,随Zn2+掺杂量的增加,荧光强度表现出先增加后减小,但并没有改变上转换发光机制;Zn2+从替代式掺杂逐渐转变成间隙式掺杂,最后以氧化锌形式析出。分析认为Zn2+的掺杂向晶格中引入了大量氧空位缺陷,造成晶格对称性降低,导致荧光增强。以Y₂O₃:Ho,Yb荧光粉为研究对象,考察了不同Ho³⁺掺杂浓度对应的上转换发光机制。研究发现,敏化剂浓度不变的情况下,随Ho³⁺浓度减小整体荧光强度增加。结合速率方程分析发现,中间能级5I6和5I7的布居方式影响上转换发光机制。实验结果表明,向基质晶格中适当引入缺陷造成的晶格对称性降低以及适当调节激活离子和敏化剂的浓度可以提高上转换荧光强度。分别以多掺杂和荧光粉混合的方法对上转换荧光进行颜色调制。对Y₂O₃:Ho,Tm,Yb的多色上转换荧光进行考察并讨论了Tm³⁺和Ho³⁺之间的能量传递。研究发现随Ho³⁺离子浓度增加,Ho³⁺（5I6）与Tm³⁺（3H5）之间的能量传递增强,同时,上转换荧光颜色得到调节。以不同质量比混合Gd₂O₃:6Er和Gd₂O₃:0.2Tm,3Yb多晶粉末得到多色上转换荧光粉,通过调整质量比以调节混合荧光的颜色及相关色温。荧光粉的SiO2包覆阻止了颗粒间的荧光再吸收并提高了粉体的涂覆性能。这种方法几乎不受掺杂浓度引起的荧光淬灭影响,可以极大的利用具有最佳发光强度的荧光粉,因此得到的多色荧光粉的发光亮度最高。本文介绍了蔗糖燃烧法合成粉体发光材料,尝试了掺杂及结构改变增强荧光发射,分别利用多掺杂和混合荧光粉的方法对上转换荧光粉进行颜色调制并利用SiO2包覆技术增强荧光粉的涂覆性能。本文的工作将会降低传统荧光粉的合成成本,同时,对上转换荧光粉在显示方面的应用做了一系列的前期工作,对于稀土掺杂荧光粉的发光机制研究及其应用推广起到了积极的作用。更多还原

【Abstract】 Since Y₂O₃:Eu oxides were found to be efficient red phosphors in 1964, the rare-earth luminescent materials developed quickly and played an important role in fields of information displaying, lighting, photoconduction device and so on. Display technology has developed on the direction of high resolution, digitalized, flattening, therefore, new requirements were presented for the researches of rare-earth luminescent materials. On the other hand, the popular of high power infra-laser diode promotes the investigation of upconversion （UC） display devices. In the present thesis, sucrose combustion synthesis was proposed for nano-sized phosphors preparation. Synthetic mechanisms and factors which impact on the surface morphology and luminescent properties were discussed. Using the phosphors for displaying and lighting as investigated subjects in this thesis, the synthetic methods, ways for enhancements of luminescence intensity, color adjustments and coating techniques were investigated both in experimental and theoretical demonstration.Phosphors Y₂O₃:Eu and Gd₂O₃:Eu were prepared using sucrose combustion method. The chelating mechanisms and experimental conditions on the surface morphology and luminescent properties were discussed. The crystallization temperature was lowed after the sucrose combustion; it was found that there was a competition between the heat and gases engendered during the sucrose combustion,which would greatly affect the size, morphology and luminescent properties of particles. Experimental results showed that the surface state Eu³⁺ can be greatly decreased with high post-treated temperature and sucrose content. The results show that the sucrose combustion synthesis method can be used as a low cost and easily generalized preparation way for other kinds of luminescent materials.Stokes and Anti-stokes （upconversion） emissions of monoclinic phase Gd₂O₃:Er with low symmetry were investigated. The dependence of doping concentration on the luminescence properties and mechanisms was discussed in details. With the increasing of doping concentration, luminescence intensities were obviously enhanced. Comparing investigation with cubic Gd₂O₃:Er, the monoclinic phase provides with more lattices, which will be much more efficient for energy transfer and UC emissions. Based on the rate equations, the increasing of red and blue light can be attributed to the energy transfer, 4I11/2+4I11/2→4F9/2+4I13/2, between two Er³⁺ ions nearby. It comes to the conclusion that, the UC emissions of monoclinic phase will be more efficient than the cubic phase Gd₂O₃.UC luminescence enhancing was realized by impurity doping or sensitizer introducing into the host lattice. UC luminescence of Gd₂O₃:Zn,Er showed that the luminescence increase with the Zn2+ doping concentration elevated. Structral analysis revealed that the dopant Zn2+ changes from substitutional doping to interstitial doping and precipitated in the form of ZnO. It was found that the oxygen vacancies by Zn2+ introducing will greatly decrease the symmetry of host lattices, which will result in the luminescence increasing. UC mechanisms of Y₂O₃:Ho,Yb were studied by variable Ho³⁺ concentration. It was found that the intensity of upconverion luminescence increased with the Ho³⁺ concentration decreasing. Ratio equation analysis found that the intermediate level 5I6 and 5I7 will greatly affect the UC mechanisms. The lowing of symmetry for host material by defects introducing or proper ratio of activator and sensitizer will both improve the UC emissions.Color adjusting for UC luminescence was by the way of multi-doping or phosphors mixing. Muti-color UC emissions in Y₂O₃:Ho,Tm,Yb were investigated and the possible energy transfer between Tm³⁺ and Ho³⁺ was discussed. With the increasing of Ho³⁺ concentration, the energy transfer between 5I6 (Ho³⁺) and 3H5 (Tm³⁺) became efficient. Meanwhile, the color of luminescence was modulated. Mixed phosphors were made up of the monoclinic Gd₂O₃:6Er and Gd₂O₃:0.2Tm,3Yb phosphors. The color and correlated color temperature can be tuned by mass ratios. Silica coated on the phosphors will inhibit the re-absorption of the luminescence and also improve the paintability of the phosphors. By mixing different phosphors, the concentration quenching can be easily avoided and the resulting color can be manageable in some extent. Using the most efficiency phosphors, the highest mulit-color can be obtained. In this thesis, sucrose combustion synthesis method was tried to fabricate the luminescent materials and luminescence enhancements by impurity doping or structure changing were discussed. The luminescence color was adjusted by directly co-doping in one host or mixing different phosphors. The silica coating on the phosphors will greatly improve the paintability. The work will greatly decrease the cost of traditional synthesis and promote the application of UC phosphors, which will be an active improvement both in emission mechanisms and applications.更多还原