Synthesis and Comparative Spectroscopic Investigation of Single Crystals and Nanocrystalline Materials toward Efficient Upconversion Luminescence (ClaraLUx)

基于掺镧上转换(UC)晶体的发光纳米材料的快速发展需要新的合成方法、创新的材料和对UC系统中的光物理过程进行更深入的研究。德国卡尔斯鲁厄理工学院(KIT)、柏林洪堡大学(HUB)和俄罗斯科学院普罗霍罗夫物理研究所(GPI RAS)开展的德俄联合研究项目ClaraLUx的目标是合成基于碱土氟化物(如CaF2、SRF2、BaF2和PbF2)共掺Yb3+/Er3+、Yb3+/TM3+和Yb3+/HO3+离子对的新型高效UC材料。这是第一次将对UC特性的系统研究应用于如此广泛的尺寸范围的晶体材料：从纳米晶体到单晶(厘米大小)，具有相同的化学成分。ClaraLUx项目将利用俄罗斯在单晶生长方面的专业知识、中心关于纳米晶体合成的知识以及该试剂盒在用各种光学方法表征UC材料方面的经验。单晶的生长将通过垂直定向结晶的方法在GPI RAS进行，而纳米晶体的合成将通过在中心开发的独特的氟解溶胶-凝胶合成方法进行。利用X射线衍射、傅里叶变换红外光谱和拉曼光谱、高角度环形暗场扫描透射电子显微镜结合能量色散X射线光谱和激光烧蚀电感耦合等离子体质谱等方法研究合成材料的结构特性。该试剂盒将表征晶体在宽温度范围(从4K到700K)的光致发光特性(稳态和时间分辨光致发光测量)。为了了解位置对称性、掺杂离子的团簇和声子能量对UC光致发光的影响，我们将对新材料的光物理性质和结构性质进行关联。此外，我们提出的方案的强大的实验优势是利用基于积分球的技术在试剂盒上准确地测量PLQY的绝对值。

The rapidly growing area of luminescent nanomaterials based on lanthanide-doped upconversion (UC) crystals requires novel synthetic methods, innovative materials and deeper investigations of photophysical processes in UC systems. Despite the significant progress made in the development of UC materials, their relatively low photoluminescence quantum yield (PLQY) and high excitation intensity remain as research challenges, thus remarkably hindering many potential applications.The joint German-Russian research project ClaraLUx between Karlsruhe Institute of Technology (KIT), Humboldt University of Berlin (HUB) and Prokhorov General Physics Institute of the Russian Academy of Sciences (GPI RAS) has the goal of synthesizing new efficient UC materials based on alkaline earth fluorides hosts (e.g. CaF2, SrF2, BaF2 and PbF2) co-doped with Yb3+/Er3+, Yb3+/Tm3+ and Yb3+/Ho3+ pairs of ions. This is for the first time when a systematic investigation of UC properties will be applied to crystalline materials in such a broad range of sizes: from nanocrystals to single crystals (centimeter size), with the same chemical compositions. The ClaraLUx project will utilize the Russian expertise in the growth of single crystals, the knowledge of the HUB regarding the synthesis of nanocrystals and the experience of the KIT in the characterization of UC materials with various optical methods. The growth of single crystals will be carried out by the method of vertical directional crystallization at the GPI RAS, whereas synthesis of nanocrystals will be performed via the unique fluorolytic sol-gel synthetic method developed at the HUB. Structural properties of the synthesized materials will be investigated with methods like X-ray diffraction, Fourier-Transform Infrared and Raman spectroscopy, High-Angle Annular Dark-Field Scanning Transmission Electron microscopy combined with Energy Dispersive X-ray spectroscopy and Laser Ablation Inductively Coupled Plasma Mass spectroscopy at the KIT. Photoluminescence properties (steady-state and time-resolved photoluminescence measurements) of the crystals in a broad temperature range (from 4 K up to 700 K) will be characterized at the KIT. The correlation of photophysical and structural properties of new materials will be performed in order to understand the impact of site symmetry, clustering of dopant ions and phonon energy on UC photoluminescence. In addition, the strong experimental advantage of our proposal is the accurate measurement of absolute values of PLQY at the KIT by using the technique based on integrating sphere.