Development of optical spin-resonance methods with advanced light sources

半导体和绝缘体的光学和电子特性强烈依赖于其内部所含缺陷的存在，它们的研究对新型光电材料的发展具有深远的影响。电子自旋共振（ESR）测量在确定缺陷的电子和结构特性方面特别有价值，但ESR实验中光激发/检测能力的耦合提供了极有价值的附加信息。在这方面已经部署了两种传统的通用方法。(i)在可调谐光源照明期间监测ESR缺陷信号可以提供有关缺陷的额外光学参数，例如陷阱深度和激发态位置（本质上是光学吸收实验和ESR的结合）。（ii）如果材料的发光依赖于自旋（例如，在供体-受体对重组中），则发光可以携带ESR信号（磁共振光学检测，ODMR），这为特定发光发射过程的特定缺陷提供了直接和明确的归属。在适当的实验室光激发源广泛可用的中等带隙能量（Eg<~3eV）半导体中，ODMR已被证明在理解缺陷与发光之间的联系方面特别成功。相比之下，在宽间隙材料（如氮化硼和氮化铝（Eg~6eV））上几乎没有开展类似的工作，但这些材料在未来发展UV光电器件（激光器，led等）中具有潜在的重要意义。这种研究的主要障碍是提供合适的高能实验室光激发源。然而，在国内和国外都有适合这些实验的光源；同步加速器光源和更复杂的激光系统（包括光学和自由电子）可以潜在地用于研究。此外，结合ODMR和相关的x射线吸收光学探测（ODXAS）的可能性特别有吸引力，因为结合的测量方法将使样品的光学发射特性与晶格结构及其中包含的缺陷之间建立直接联系。由于这种方法是完全独特的，目前世界上还没有合适的实验能力来进行这种科学研究。因此，提出的工作的核心目标是开发这种能力，并通过应用于一些对开发新的紫外光电器件（led，激光器等）特别感兴趣的宽带隙材料来证明其有效性，并在了解适合在癌症放疗领域部署的辐射监测的材料中。这项工作将使英国在开发这种先进分析方法方面处于领先地位，并且是在计划中的先进光源（如4GLS和XFEL）上进行新实验的必要先决条件。

The optical and electronic properties of semiconductors and insulators are strongly dependent on the presence of defects contained within them, and their study has profound influence on the development of new optoelectronic materials. Electron spin resonance (ESR) measurements are particularly valuable in determining the electronic and structural properties of the defects, but coupling of light excitation/detection capabilities within the ESR experiment provides extremely valuable additional information. Two traditional generic methods have been deployed in this respect. (i) Monitoring of the ESR defect signals during illumination with tuneable light sources can provide additional optical parameters of the defects concerned, such as trap depth and the location of excited states (essentially a marriage of optical absorption experiments and ESR). (ii) Where the luminescence of a material is spin dependent (e.g. in donor-acceptor pair recombination), ESR signals can be carried by the luminescence (Optical Detection of Magnetic Resonance, ODMR), and this provides direct and unequivocal attribution of particular defects with specific luminescence emission processes.ODMR has proved particularly successful in understanding the link between defects and luminescence in semiconductors of moderate band-gap energies (Eg<~3eV) where suitable laboratory light excitation sources are widely available. In contrast, virtually no comparable work has been undertaken on wider-gap materials such as Boron Nitride and Aluminium Nitride (Eg~6eV), yet these classes of materials are potentially of great future importance in developing UV optoelectronic devices (lasers, LEDs etc). The main obstacle to such studies is in the provision of suitable high-energy lab-based light excitation sources. However, appropriate light sources for these experiments are available both in this country and overseas; synchrotron light sources and more complex laser systems (both optical and free-electron) can potentially be exploited for the research. Furthermore, the possibilities for combing both ODMR and the associated Optical Detection of X-ray Absorption (ODXAS) is particularly attractive, since the combined measurement method would enable a direct link between the optical emission properties of a sample, and structure of both the lattice, and the defects contained within it. As this approach is completely unique, no suitable experimental capabilities exist worldwide at present that can undertake such science. A core goal of the proposed work is thus to develop such capabilities, and demonstrate the effectiveness by application to a number of wide band-gap materials of particular interest to the development of new UV optoelectronic devices (LEDs, lasers etc), and in the understanding of materials suitable for radiation monitoring deployed in the fields of cancer radiotherapy. The work will establish the UK at the forefront in developing such advanced analytical methods, and is a necessary pre-requisite to new experiments on the planned advanced light sources such as 4GLS and XFEL.