Borosulphates as Host Structures for Luminescent Materials and for Non-Linear Optical Properties

• Applicant: Professor Dr. Henning Höppe
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Synthesis and Properties of Functional Materials
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 338584357

Borosulphates are silicate-analogous compounds containing anions, which comprise sulphate tetrahedra bound covalently to tetrahedral or trigonal planar borate ions. Chemically these behave like the relatively thoroughly investigated Borophosphates. The first approximately eighty crystalline examples published so far, confirm the strong similarity to silicate structures. Such silicate-analogous compounds are interesting for several reasons. They open a great and per se highly interesting structural chemistry, and these novel compounds provide many topics for the investigation of structure-property relations. Our focus lies in the search for new luminescent compounds suited for white light emitting diodes, phosphor tubes, thermometry or as scintillators. Moreover, we consider non-linear-optical properties of suited candidates which might be employed in lasers for frequency doubling. Here, especially compounds are interesting showing large bandgaps which is the case for borosulphates. Other properties like acid-base behaviour as well as catalytic properties will be considered, too.In this project we continue the systematic and explorative investigation of the novel compound class of crystalline borosulphates. In this project we will focus on representatives doped with outer and inner transition metal ions (d and f elements). We expect besides the discovery of new structural features an extraordinarily rich crystal chemistry; in such structures the probability grows that these lack inversion symmetry and thus show non-linear optical properties – borates and tetrahedral units foster that. We expect deeper insight in the coordination behaviour of borosulphates, such as ligand-field effects and the nephelauxetic effect; this will be helpful for basic research as well as for possible future applications. Methodically we will use the single-crystal x-ray diffraction for the structure determination. The purity of our synthesised samples will be checked and new compounds will be identified by powder x-ray diffraction. We will additionally characterise the thermal behaviour of the new compounds using diffractions methods and classic thermal analysis like DTA/TG. We examine the optical properties by optical spectroscopy (fluorescence and UV-Vis-spectroscopy) supported by theoretical calculations. Suited compounds will be scrutinised regarding non-linear-optical properties. Especially on amorphous powder samples we plan boron m. a. s. n. m. r. measurements for the determination of the local structure. Moreover, we plan magnetic measurements for the identification of valence states and possible magnetic ordering.

• DFG Programme: Research Grants