摘要
稀土发光材料在照明、显示显像、固体激光器、光存储及光通讯等领域已获得广泛应用,近年来,对稀土掺杂基质材料进行研究以提高发光效率、化学稳定性及使用寿命成为该领域的研究热点。Al2O3具有机械强度高、热传导性好、化学稳定性优良以及透明性好等特点,作为稀土掺杂基质材料受到研究人员的广泛关注。目前,粉体基质的纳米化及其分散性以及薄膜基质的透明性是研究的两个重要方向。
本文研究了Al2O3基质材料的溶胶-凝胶制备过程,重点对Al2O3溶胶制备规律、Al2O3纳米粉体分散性以及Al2O3薄膜透明性等关键问题进行了考察,并在此基础上研究了Eu3+、Tb3+掺杂的Al2O3纳米粉体及透明薄膜的发光特性。论文主要研究内容及结论如下：
1、开展了Al2O3溶胶的制备规律研究,结果表明水解温度会影响溶胶晶粒的形成和生长过程,在水解温度为60-80℃时,可制得稳定的勃姆石(γ-AlOOH)结构Al2O3溶胶；随陈化时间的延长,溶胶粘度增大,原先细小的溶胶粒子逐渐聚集长大形成长度约50 nm的纤维状粒子；酸的种类和用量会改变溶胶体系的电荷环境及胶粒表面的双电层结构,适当强酸的加入(pH=2.73～3.20)有利于获得稳定的溶胶；增加水用量可促进前驱体水解,有利于获得结晶完善的勃姆石Al2O3溶胶；通过添加表面活性剂可有效减少溶胶粒子之间的聚集,提高溶胶稳定性。
2、开展了Al2O3纳米粉体制备研究,结果表明混合溶剂和表面活性剂(PEG1000)共同作用可有效解决Al2O3纳米粉体团聚问题。在煅烧分解的过程中,PEG1000减少了Al2O3晶粒之间的离子扩散,提高了Al2O3纳米粉体的分散性。随煅烧温度升高,Al203存在γ-AlOOH→γ-Al2O3→θ-Al2O3→a-Al2O3的相转变过程,粒径则呈现出先减小后增大的变化趋势。
3、开展了Al2O3透明薄膜制备研究,结果表明Al2O3薄膜的光透过率与晶粒结构密切相关。薄膜中Al2O3晶粒的择优取向生长大幅降低了薄膜的反射系数(M)和散射系数(S),提高了薄膜透光率；煅烧导致薄膜中氧空位缺陷逐渐减少,减弱了对光的吸收,在800℃煅烧后薄膜光透过率达最高；而在900℃煅烧后,薄膜中生成的θ-Al2O3导致了薄膜光透过率降低。
4、开展了Eu3+、Tb3+掺杂Al2O3纳米发光粉体及透明薄膜的发光特性研究。结果表明所制备的纳米发光粉体平均晶粒尺寸为10 nm左右,粒子呈颗粒状,分散性较好；而发光薄膜透明性良好,且表面致密、平整、无裂纹产生。材料的发光性能主要受煅烧温度和掺杂浓度的影响,最佳的煅烧温度为800℃,Eu3+离子最佳掺杂浓度为10 mol%,Tb3+离子最佳掺杂浓度为5 mol%。
Rare earth luminescent materials have been widely used in lighting, display imaging, solid-state lasers, optical storage and optical communication and other fields. In recent years, the research of rare-earth-doped substrate materials for improving the luminous efficiency, mechanical properties, chemical stability and life become a research hotspot in the field. Alumina has high mechanical strength, good thermal conductivity, chemical stability and good transparency, and draws many researchers' attention. At present, the nanocrystallization of the powder and its dispersion, as well as the transparent substrate film are two important directions.
In this paper, the Al2O3 was used as the rare earth ions doped substrate, the sol-gel preparing process of Al2O3 was studied, with emphasis on the preparation of the laws of Al2O3 sol, Al2O3 nanocrystlline powder dispersion and the transparency of Al2O3 films. Based on that, the photoluminescence properties of Eu3+ doped and Tb3+ doped Al2O3 nanocrystalline powders and their transparent film were investigated. The major research contents and the conclusions were as follows:
1. The preparation of Al2O3 sol were carried out. The results show that the hydrolysis temperature will affect the grain size of sol formation and growth process. When the hydrolysis temperature is 60-80℃, the stable boehmite (γ-AlOOH) structure sol can be obtained; with extended aging time, the sol viscosity increased, the original small particles of the sol gradually grow together to form the fibrous particles with the length of 50nm; the type and the concentration of the acid will change the charge-environment of the sol system and the double-layer structure of the sol surface, the appropriate addition of strong acid (pH= 2.73～3.20) was in favor of the sol stability; the increase in the amount of water can promote precursor hydrolysis, and is conducive to improve the crystallization of the boehmite sol. Furthermore, adding the surfactant can effectively reduce the aggregation between the sol particles to enhance the stability of sol.
2. The preparation of Al2O3 nanocrystalline powder was carried out. The results showed that the mixed solvent and surfactant (PEG 1000) can be an effective solution to the combined effect of Al2O3 nanocrystalline powder reunion. In the process of calcination decomposition. PEG1000 reduce the Al2O3 ion diffusion between the grains and improve the Al2O3 nanocrystalline powder dispersion. With the increasing of the heat treatment temperature, Al2O3 had the phase transformation process ofγ-AlOOH→γ-Al2O3→θ-Al2O3→α-Al2O3, and the grain size is reduced firstly and then incline to increase.
3. The preparation of transparent Al2O3 film was carried out. The results showed that the light transmittance of the Al2O3 film is closely related to the microstructure. Al2O3 films grain growth of the preferred orientation of the film significantly reduce the reflection coefficient (M) and scattering coefficient (S), to improve the film transmittance; calcination led to the film gradually reduce the oxygen vacancy, and has reduced the absorption of light. After calcined at 800℃, the optical transmittance was maximum; and calcined at 900℃, theθ-Al2O3 generated in the films resulted in lower light transmittance.
4. The photoluminescence properties of Eu3+ and Tb3+ doped Al2O3 nanocrystalline powders and their transparent films were analysed. The results show that the average grain size of the nanocrystalline luminescent powder was about 10 nm, with granular particles, good dispersion and good transparency, and the surface is dense and smooth without cracks. Luminescence properties of the materials were mainly affected by the calcination temperature and doping concentration. The best calcination temperature is 800℃, the doped concentration of Eu3+ is 10 mol%, the doped concentration of Tb3+ is 5 mol%.
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