MRI: Acquisition of Equipment for Thermal and Optical Studies of Sol-gel Materials Containing Rare Earth Ions

溶胶-凝胶合成为制备光学透明的非晶态材料提供了一种低温手段，这种材料比传统的热淬火熔融材料制造的玻璃更安全、更节能、成本更低。溶胶-凝胶合成的一个吸引人的方面是，干燥凝胶的光学性质已经退火到接近~1000℃的温度，类似成分的熔融玻璃。掺杂稀土离子的溶胶-凝胶材料广泛应用于激光、环境和生物传感器、太阳能聚光器、有源波导、荧光粉和其他光子材料等光学领域。从基础的角度来看，在溶胶-凝胶中加入稀土离子是很有趣的，因为通过研究寄主对稀土离子光学性质的影响，可以获得有关寄主性质的信息，以及寄主和稀土交换能量的方式。需要对相关的能量传递相互作用有更全面的了解。以前的工作集中在干燥凝胶或完全退火玻璃的光谱研究上。相比之下，该项目提出将材料从干燥凝胶加工成玻璃时的光学行为与RE环境的变化联系起来。在溶胶-凝胶材料的演化过程中，热力学测量将提供有关主体成分和结构的信息，外加电场将通过控制材料内自由离子的存在和运动来改变RE局部环境。有了这些信息，希望可以改善光学性质，使这些材料可以找到更大的实际应用。本本科生课题将研究含稀土离子的溶胶-凝胶材料。溶胶-凝胶法是一种制备透明介质的低温方法，该透明介质可以容易地掺杂各种光学活性元素。掺杂稀土离子的溶胶-凝胶材料被广泛应用于激光、环境和生物传感器、太阳能聚光器、有源波导、荧光粉和其他光子材料。已经确定了两个限制掺杂光学活性稀土离子的溶胶-凝胶材料的荧光产率的问题：羟基的存在通过多声子弛豫提供了非辐射途径，稀土离子的聚集促进了能量迁移和交叉弛豫。该项目将遵循新的研究路线来解决这些重要问题。在溶胶-凝胶材料演变过程中的热力学测量，如同步差示扫描量热法和热重分析，将提供有关干燥凝胶在加热时致密的主体成分和结构的信息。此外，外加电场将通过控制自由离子组分的存在来改变RE局部环境。在合成过程的所有阶段，将使用稀土光谱来探测材料，提供补充从热学和电学实验中获得的知识的信息。在溶胶-凝胶材料完全致密化后，将使用时间分辨光谱测量和光谱孔燃烧（一种高分辨率饱和光谱技术）来研究RE离子之间能量传递相互作用的性质。希望通过这些研究可以提高这些材料的量子产率和其他光学性质。

Sol-gel synthesis provides a low temperature means for preparing optically transparent amorphous materials that are safer, more energy efficient and more cost effective to produce than traditional glasses made by thermally quenching molten material. One attractive aspect of sol-gel synthesis is that the optical properties of a dry gel that has been annealed to temperatures near ~1000 C approach that of a melt glass of similar composition. Sol-gel materials doped with rare earth (RE) ions are used in many optical applications including lasers, environmental and biological sensors, solar concentrators, active waveguides, phosphors and other photonic materials. The incorporation RE ions in sol-gels is interesting from a fundamental standpoint because information about the nature of the host, and how the host and RE exchange energy, may be gained by studying the host's influence on the optical properties of the RE ion. A more complete understanding of the relevant energy transfer interactions is needed. Previous work has concentrated on spectroscopic studies of either dried gels or fully annealed glasses. In contrast, this project proposes to correlate optical behavior with changes in the RE environment as the material is processed from dried gel to glass. Thermodynamic measurements during the evolution of the sol-gel materials will provide information about the host composition and structure, and an applied external electrical field will be used to modify the RE local environment by controlling the presence and motion of free ions within the material. With this information, it is hoped that the optical properties can be improved so that these materials may find greater practical application. This undergraduate research project will study sol-gel materials containing rare earth (RE) ions. The sol-gel process is a low temperature method for preparing transparent media that may easily be doped with a variety of optically active elements. Sol-gel materials doped with RE ions are used in many applications including lasers, environmental and biological sensors, solar concentrators, active waveguides, phosphors and other photonic materials. Two issues have been identified that limit the fluorescence yield of sol-gel materials doped with optically active RE ions: the presence of hydroxyl groups provides non-radiative pathways via multi-phonon relaxation, and the clustering of RE ions facilitates both energy migration and cross relaxation. This project will follow new lines of inquiry to address these important problems. Thermodynamic measurements during the evolution of the sol-gel materials, such as simultaneous differential scanning calorimetry and thermogravimetric analysis, will provide information about the host composition and structure as a dry gel densifies upon heating. Further, an applied external electrical field will be used to modify the RE local environment by controlling the presence of free ionic components. At all stages in the synthesis process, RE spectroscopy will be used to probe the materials, providing information that complements the knowledge gained from the thermal and electrical experiments. After the sol-gel materials are fully densified, the nature of energy transfer interactions among RE ions will be investigated with time-resolved spectroscopic measurements and with spectral hole burning, a high resolution saturation spectroscopy technique. It is hoped that through these studies the quantum yield and other optical properties of these materials can be improved.