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

• Applicants: Professor Dr. Erhard Kemnitz; Dr. Andrey Turshatov
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448730215

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.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Dr. Sergey Kuznetsov, until 3/2022
• Co-Investigator: Professor Dr. Bryce Richards