Si- and Ge-mullite single crystals doped with foreign cations

近几十年来，对莫来石性能的深入研究主要集中在莫来石粉末和多晶莫来石陶瓷上。关于莫来石单晶的合成和表征的研究文献很少。掺杂稀土元素的莫来石的单晶没有发现，尽管这些材料显示出与相应粉末材料相同的有趣的发光特性。本项目的首要目的是研究稀土元素（Eu, Tb， Gd等）在莫来石结构中的掺入机理，并确定其具有潜在应用价值的发光性能。为此，稀土掺杂莫来石单晶（2:1莫来石，2Al2O3）。将采用Czochralski法合成厘米级的SiO2。它们将通过微化学、光谱和晶体化学方法进行表征。该项目的第二个目标侧重于稀土元素与“单对元素”（Pb, Bi）结合在锗莫来石类似物“锗莫来石”（3al2o3）中的基本晶体化学研究。2 geo2)。将在含铅或含铋高温熔体中进行一系列稀土掺杂锗莫来石的通量实验。本基础研究旨在揭示莫来石晶体结构中具有孤电子对的外来阳离子复杂而新颖的掺入机理。为此，首次合成了稀土掺杂硅莫来石大晶体和锗莫来石掺杂单晶，并对其进行了基本表征。最后，就一般意义上的莫来石而言，这些贡献可能对莫来石材料的发展具有重要意义。

Intensive research on the properties of mullite was mainly performed on mullite powders and polycrystalline mullite ceramics within the last decades. Little work was documented on synthesis and characterization of mullite single crystals. There is no information on single crystals of mullites doped with rare-earth (RE) elements, although these materials display interesting luminescence properties as shown on corresponding powder materials. The first aim of this project is to study the incorporation mechanism of RE elements (Eu, Tb, Gd etc.) into the mullite structure and to determine their photo-luminescent properties with potential applications. For this aim RE-doped mullite single crystals (2:1 mullite, 2Al2O3 . SiO2) of centimeter size will be synthesized by the Czochralski method. They will be characterized by microchemical, spectroscopic and crystal-chemical methods. A second aim of the project focusses on the basic crystal-chemical study of the incorporation of RE elements combined with "lone-pair-elements" (Pb, Bi) in the germanium analog of mullite, 'germanium-mullite' (3 Al2O3 . 2GeO2). The synthesis will be performed in a series of flux experiments of RE-doped germanium mullites out of Pb- or Bi-containing high-temperature melts. This basic research study intends to shed light on the suggested complex and novel incorporation mechanism of foreign cations with lone electron pairs in the mullite crystal structure. For this purpose, for the first time large RE-doped Si-mullite crystals and doped single crystals of Ge-mullite are synthesized and fundamentally characterized. Finally, with respect to mullite in a general sense, the contributions may be of great importance for the development of mullite materials.