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

溶胶-凝胶合成提供了用于制备光学透明的无定形材料的低温手段，与通过热淬火熔融材料制备的传统玻璃相比，所述光学透明的无定形材料更安全、更节能并且生产成本更有效。 溶胶-凝胶合成的一个有吸引力的方面是已经退火到接近1000 ℃的温度的干凝胶的光学性质接近类似组成的熔融玻璃的光学性质。 掺杂有稀土（RE）离子的溶胶-凝胶材料用于许多光学应用，包括激光器、环境和生物传感器、太阳能集中器、有源波导、磷光体和其它光子材料。 从基本的观点来看，在溶胶-凝胶中掺入RE离子是有趣的，因为关于宿主的性质以及宿主和RE如何交换能量的信息可以通过研究宿主对RE离子的光学性质的影响来获得。 需要更全面地了解相关的能量转移相互作用。 以前的工作集中在干凝胶或完全退火玻璃的光谱研究。相比之下，该项目提出将光学行为与RE环境中的变化相关联，因为材料从干凝胶加工成玻璃。在溶胶-凝胶材料的演变过程中的热力学测量将提供有关的主机组成和结构的信息，并施加外部电场将被用来修改RE局部环境，通过控制材料内的自由离子的存在和运动。有了这些信息，希望可以改善这些材料的光学性能，使这些材料可以找到更大的实际应用。 本研究计画将研究含稀土离子之溶胶-凝胶材料。 溶胶-凝胶法是一种低温制备透明介质的方法，可以很容易地掺杂各种光学活性元素。 稀土离子掺杂的溶胶-凝胶材料在激光器、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领域有着广泛的应用。 已经确定了限制掺杂有光学活性RE离子的溶胶-凝胶材料的荧光产率的两个问题：羟基基团的存在通过多声子弛豫提供非辐射途径，并且RE离子的聚集促进能量迁移和交叉弛豫。 该项目将采用新的调查路线来解决这些重要问题。 在溶胶-凝胶材料的演变过程中的热力学测量，如同时差示扫描量热法和热重分析，将提供关于主体组成和结构的信息，因为干燥凝胶在加热时致密化。 此外，施加的外部电场将用于通过控制自由离子组分的存在来修改RE局部环境。 在合成过程的所有阶段，RE光谱将用于探测材料，提供补充从热和电实验中获得的知识的信息。溶胶-凝胶材料完全致密化后，稀土离子之间的能量转移相互作用的性质将与时间分辨光谱测量和光谱烧孔，高分辨率饱和光谱技术进行研究。 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.