Research Areas
1. Luminescent materials with "antenna"
Halide derivatives of rare-earth metal oxidomolybdates and -tunstates bearing complex molybdate and tungstate entities exhibit a ligand-to-metal charge transfer (LMCT) which can be utilized as sensitizer ("antenna") to excite luminescence in acitve cations present in respective host materials. Enlarging the coordination number around the Mo6+ and W6+ cations, respectively, or increasing the size of the aforementioned units itself by condensation delivers variations of the LMCT band towards lower energies. The primary goal is to leave the area of UV radiation for the visible spectrum to create materials that can be excited with a blue LED.
2. Seven Up - Lithium-Incorporation
The incorporation of Li+ into the rare-earth metal molybdates and tungstates results in facinating new structures and with exciting properties. Very often the integration is reductive, thus the molybdenum and tungsten cations, respectively, are not able to keep their highest oxidation state. The partial reduction leads to strongly colored materials (keyword: pigments) and the appropriate behavior in the magnetic field and the EPR spectrum.
3. Variationa on a theme
The aformentioned halide derivatives of rare-earth metal molybdates and tungstates provide a scope for numerous substitution variants, which include both the exchange of the halide for other monovalent anions (e. g. hydroxide) and the the replacement of trivalent rare-earth metal by bismuth. Furthermore an exchange of the ligand sphere within the complex units form oxide to sulfide anions is also possible.
Synthesis and structure
A main aspect of the above mentioned reaearch topics is the single phase synthesis and the crystal structure determinations of new materials. Therefore, different synthesis methods, from solid-state synthesis to solvochemical techniques to of high-pressure processes.
The characterization of the obtained products is performed by single-crystal and powder X-ray diffractions as well as vibrational spectroscopy (IR and Raman) and electron microprobe analysis.
Characterization of the properties
Luminescence
The doping of suitable host materials with active cations leads to luminescent materials. Their optical properties are investigated by diffuse reflectance spectroscopy as well as photoluminescence spectroscopy (in coorperation with the group of Prof. Dr. Henning Höppe at the University of Augsburg).
Magnetism
The behavior of the synthesized materials in the magnetic field can be of interest if open-shell rare-earth metals interact with transition metals. Hence, appropriate compunds are investigated reagrding their magnetic susceptibility.
Ingo Hartenbach
Prof. Dr. rer. nat.Group Leader