Coherent spectroscopy as a new luminescent materials characterisation tool

稀土掺杂材料在LED和照明、激光和闪烁材料以及太阳能电池中的能量转换器等方面的应用引起了人们的极大兴趣。近年来，三价稀土离子掺杂材料在量子信息存储与处理、医学成像和高稳定激光锁定等方面的应用引起了人们的极大兴趣。后者直接与三价稀土金属离子及其长寿命光谱空穴的光学跃迁的窄而均匀的线宽或相当长的相干寿命有关。尤其是Eu3+非常适合观察窄而均匀的线宽。由于均匀的线宽/相干寿命对激活剂离子的局域环境中的外部扰动非常敏感，如缺陷、自旋波动或局域无序引起的低频振动模，在名义上等效的材料中，它们的值可以变化几个数量级。因此，它们允许对当地环境进行非常敏感的探测，例如通过研究光子回波。然而，到目前为止，对其相干特性的研究主要集中在高质量的大块单晶上。然而，最近有研究表明，在高散射粉末中可以观察到光子回波发射。因此，在这个项目中，我们打算利用相干光谱作为一种材料表征工具，最终将有助于改善材料的性能，例如在高性能荧光粉中。它的应用将提供有关材料的当地化学环境的信息，这是传统光谱学无法获得的。系统地研究通过不同制备方法制备的Eu3+和Eu2+样品的相干性质，结合传统的光谱和附加的表征方法，将有助于揭示相干性质与局部环境的关系，最终有助于改进光学材料的合成设计，例如高性能荧光粉。在第一步中，将研究模型体系Y2O3：Eu3+，该体系已经使用常规光谱进行了研究。然后，这些研究将扩展到Y2SiO5：Eu3+，一种可能的量子计算候选者。最后，该方法还将在Eu2+掺杂材料上进行测试，以研究尽管Eu2+的相干寿命相对较短，但能否获得改善Eu2+掺杂发光材料的重要信息。通过这项研究，我们希望有助于更好地了解当地环境对光学材料性能的影响。

Rare earth doped materials are of great interest for the application in LEDs and lighting, laser and scintillation materials, and energy converters in solar cells. Lately, especially materials doped with trivalent rare earth ions have arisen much interest as materials for quantum information storage and processing, medical imaging and highly stable laser locking. The latter are directly related to the remarkable narrow homogeneous linewidths, or equivalently long coherence lifetimes of optical transitions of trivalent rare earth metal ions as well as their long-lived spectral holes. Especially Eu3+ is ideally suited for the observation of narrow homogeneous linewidths. Since the homogeneous linewidths/coherence lifetimes are extremely sensitive to external perturbations within the local environment of the activator ion, such as defects, fluctuating spins or low frequency vibrational modes caused by local disorder, their values can vary by several orders of magnitude in nominally equivalent materials. Thus, they allow a very sensitive probe of the local environment, for instance by studying photon echoes. However, so far studies on the coherence properties have mainly concentrated on high-quality bulk single crystals. Yet, it was recently shown that photon echo emission could be observed in highly scattering powder.Within this project we therefore intend to take advantage of coherence spectroscopy as a materials characterisation tool which will ultimately help in the improvement of materials properties, e.g. in high performance phosphors. Its application will provide information on the local chemical environment of materials which is not accessible with conventional spectroscopy. A systematic study on the coherence properties of Eu3+- and Eu2+-containing samples prepared via different preparation methods, combined with conventional spectroscopy and additional characterisation methods will shed light on the relation between coherent properties and local environments and ultimately help improving the synthesis design of optical materials, e.g. of high performance phosphors. In a first step, the model system Y2O3:Eu3+ will be studied, which was already investigated using conventional spectroscopy. Those studies will then be extended to Y2SiO5:Eu3+, a possible candidate for quantum computing. Finally the method will also be tested on Eu2+-doped materials in order to investigate if important information for the improvement of Eu2+-doped luminescence materials can be obtained despite of the relatively short coherence lifetimes. With this study, we hope to contribute to a better understanding of the local environments on the properties of optical materials.