The structural origin of crystal field parameters in rare-earth doped glasses

稀土掺杂玻璃晶体场参数的结构起源

• 批准号: EP/E011799/1
• 负责人: Gavin Mountjoy
• 金额: $ 28.15万
• 依托单位: University of Kent
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FE011799%2F1
• 关键词: structural; origin; crystal; field; parameters

During recent decades optical technology has had a pronounced impact on our standard of living, by providing great improvements in communications, information technology, and medicine. Many of these applications have been made possible through the development of advanced materials, a good example being the production of optical fibres. This proposal is to advance our knowledge of the physics of materials which play a key role in optical technology. This proposal will examine optical materials which are glasses doped with rare earth elements. The importance of glasses in optics is obvious as they provide a transparent medium through which light can pass. Glass has the ability to conduct light (e.g. optical fibres), to shape light (e.g. lenses), and to host active elements which interact with light. The latter are an important area of research as they are essential for improving the efficiency of optical communications and developing optical analogues of electronics.Rare earth elements are an important type of active element. They have the property of possessing f-electrons, which absorb and emit light but which are also highly shielded, and so (largely) unperturbed by the surrounding medium. This makes rare earth elements very effective for stimulated emission of light, the phenomenon which is the basis for lasers and amplifiers.Lasers made from rare earth doped glasses are important in the applications discussed above, and also in very advanced scientific experiments. For example, one way to the create conditions for nuclear fusion is by using enormously powerful lasers, and such lasers contain several cubic metres of rare earth doped glass. Amplifiers made from rare earth doped glasses are crucial for boosting the signal in optical fibres, so that they can cross oceans (for example).The optical properties of rare earth elements are described using the theory of Quantum Mechanics. This is needed to understand they way in which f-electrons change their orbits (or wavefunctions), hence emitting or absorbing light, a process called transition . Perhaps surprisingly, small perturbations due to the surrounding atoms play a critical role in these transitions, via their influence on rare earth f-electron wavefunctions. There is a well-developed theory of how f-electron transitions depend on surrounding atoms in crystals, where the atoms have well-defined positions. The same theory has been applied to glasses. But glasses by their nature are non-crystalline, and the consequent disorder in atom positions has hindered attempts to fully explain optical properties of rare earth doped glasses. This proposal will carrying out new studies of rare earth doped glasses. It will use the experimental techniques of diffraction, which reveals glass structure, and X-ray absorption spectroscopy, which reveals rare earth sites, in combination with molecular dynamics, which creates models of atom positions. These techniques were used separately in previous studies, but this proposal will use them in combination to obtain detailed and accurate models of rare earth doped glasses.The models of rare earth doped glasses will be analysed to understand how perturbations arise from disorder in atom positions. Previous studies focussed on variations in the number of surrounding atoms, but this did not provide an explanation. This proposal will focus on variations in the symmetry of surrounding atoms, by calculating different measures of symmetry. The results will fill a significant gap in the physics describing f-electron transitions in glasses, and hence improve the understanding of optical properties of rare earth doped glasses. This will indirectly assist in the development of optical technology based on these materials, and hence their many important applications.

在最近的几十年中，光学技术通过在通信，信息技术和医学方面提供了重大改进，对我们的生活水平产生了明显的影响。通过开发高级材料，这些应用已成为可能，一个很好的例子是光纤的产生。该建议是提高我们对材料物理学的了解，这些物理在光学技术中起着关键作用。该提案将检查具有稀土元素掺杂的眼镜的光学材料。光镜中玻璃的重要性很明显，因为它们提供了一种透明的介质，光线可以通过。玻璃具有传导光（例如光纤），塑造光（例如镜头）并托管与光相互作用的活动元件的能力。后者是研究的重要领域，因为它们对于提高光学通信的效率和开发电子产品的光学类似物至关重要。RareEarth Elements是一个重要的活动元件的重要类型。他们具有拥有F-电子的特性，它吸收并发出光线，但也具有高度屏蔽，因此（很大程度上）不受周围介质的影响。这使得稀土元素对于刺激光的发射非常有效，这是激光和放大器的基础的现象。用稀土掺杂玻璃制成的激光器在上面讨论的应用中很重要，并且在非常高级的科学实验中也很重要。例如，一种创造核融合条件的方法是使用巨大强大的激光器，而这样的激光器包含几立方米的稀土掺杂玻璃。由稀土掺杂玻璃制成的放大器对于在光纤中增强信号至关重要，因此它们可以越过海洋（例如）。使用量子力学理论来描述稀土元素的光学特性。这是需要理解F-电子改变其轨道（或波形）的方式，因此发出或吸收光（称为过渡的过程）。也许令人惊讶的是，由于周围的原子对稀土F-电子波函数的影响，由于周围原子的影响在这些过渡中起着至关重要的作用。有一个完善的理论，即F-电子转变如何取决于原子具有明确位置的晶体中的周围原子。相同的理论已应用于眼镜。但是，眼镜本质上是非晶状的，随之而来的原子位置疾病阻碍了完全解释稀土掺杂玻璃的光学特性的尝试。该提案将对稀土掺杂眼镜进行新的研究。它将使用衍射的实验技术，该技术揭示了玻璃结构和X射线吸收光谱，从而揭示了稀土位点，并结合了分子动力学，从而创建了原子位置的模型。这些技术在先前的研究中分别使用，但是该提案将使用它们结合使用，以获得稀有地球掺杂玻璃的详细而准确的模型。将分析稀土掺杂玻璃的模型，以了解如何由原子位置中的无序扰动产生。先前的研究着重于周围原子数量的变化，但这并没有提供解释。该建议将通过计算不同的对称性度量来集中于周围原子对称性的变化。结果将填补描述玻璃中F-电子转变的物理学的显着空白，从而提高对稀土掺杂玻璃光学特性的理解。这将间接帮助基于这些材料的光学技术开发，因此它们的许多重要应用。