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.

近几十年来，光学技术在通信、信息技术和医学方面取得了巨大进步，对我们的生活水平产生了显着影响。其中许多应用是通过先进材料的开发而成为可能的，一个很好的例子就是光纤的生产。该提案旨在增进我们对在光学技术中发挥关键作用的材料物理学的了解。该提案将研究光学材料，即掺杂稀土元素的玻璃。玻璃在光学中的重要性是显而易见的，因为它们提供了光可以通过的透明介质。玻璃具有传导光（例如光纤）、塑造光（例如透镜）以及容纳与光相互作用的活性元件的能力。后者是一个重要的研究领域，因为它们对于提高光通信的效率和开发电子学的光学类似物至关重要。稀土元素是一种重要的活性元素。它们具有拥有 f 电子的特性，可以吸收和发射光，但也受到高度屏蔽，因此（很大程度上）不受周围介质的干扰。这使得稀土元素对于受激光发射非常有效，这种现象是激光器和放大器的基础。由稀土掺杂玻璃制成的激光器在上述应用以及非常先进的科学实验中都很重要。例如，创造核聚变条件的一种方法是使用强大的激光器，这种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增强光纤中的信号至关重要，以便它们能够跨越海洋（例如）。稀土元素的光学特性是使用量子力学理论来描述的。这是理解 f 电子改变轨道（或波函数）从而发射或吸收光的方式所必需的，这一过程称为跃迁。也许令人惊讶的是，周围原子引起的小扰动通过影响稀土 f 电子波函数，在这些跃迁中发挥着关键作用。关于 f 电子跃迁如何取决于晶体中周围的原子，有一个成熟的理论，其中原子具有明确的位置。同样的理论也适用于眼镜。但玻璃本质上是非晶体，因此原子位置的无序阻碍了充分解释稀土掺杂玻璃光学特性的尝试。该提案将开展稀土掺杂玻璃的新研究。它将使用衍射实验技术（揭示玻璃结构）和 X 射线吸收光谱（揭示稀土位点），并结合分子动力学（创建原子位置模型）。这些技术在之前的研究中是单独使用的，但本提案将结合使用它们来获得详细而准确的稀土掺杂玻璃模型。将对稀土掺杂玻璃模型进行分析，以了解原子位置无序如何产生扰动。先前的研究集中于周围原子数量的变化，但这并没有提供解释。该提案将通过计算不同的对称性度量来关注周围原子对称性的变化。该结果将填补描述玻璃中 f 电子跃迁的物理学的重大空白，从而提高对稀土掺杂玻璃光学性质的理解。这将间接有助于基于这些材料的光学技术的发展，从而促进它们的许多重要应用。