Research: Physical-inorganic chemistry. Synthesis, crystal growth, optical spectroscopy, neutron scattering, magnetic and excited-state properties of d - and f - coordination compounds.

Special courses: Spectroscopy of coordination compounds, theory of coordination compounds, molecular magnetism, neutron scattering, inorganic materials, inorganic luminescence.

Chemical synthesis is combined with a variety of physical techniques to study new inorganic materials. The optical or magnetic properties are influenced and tuned by chemical and structural variation.

Photon upconversion in lanthanide and transition metal compounds
NIR to VIS photon upconversion processes and materials are extensively studied using a variety of optical spectroscopic techniques. Both rare-earth (RE) and transition-metal (TM) systems as well as RE / TM combinations are explored. Competing radiative and nonradiative excited state processes and thus the light emitting processes are influenced by chemical variation. Understanding the basic physical mechanisms is the primary goal, but materials with high upconversion yield and a potential for applications as display phosphors or laser materials are also explored.

New scintillation materials
In collaboration with the group of C.W.E. van Eijk and P. Dorenbos in Delft we are preparing and studying new Ce³⁺ doped chloride, bromide and iodide materials with potential applications in scintillation detection of X-rays and g-rays.

Exchange and anisotropy interactions in spin clusters and single-molecule magnets
The ground-state properties of exchange-coupled spin clusters of transition metal and rare earth metal ions are studied by magnetic measurements, EPR, inelastic neutron scattering (INS) and theoretical modelling. INS is a powerful tool in evaluating competing interactions in larger clusters and in quantifying anisotropy effects. The effects of competing interactions are also studied in low-dimensional rare-earth halide systems exhibiting magnetic order at cryogenic temperatures. Neutron scattering experiments are performed at SINQ (Villigen), ILL (Grenoble), HMI (Berlin) and ISIS (Appleton).

Quantum magnetisation processes in KCuCl₃, TlCuCl₃ and NH₄CuCl₃
The title compounds exhibit ladder type structures with dominant antiferromagnetic interactions within Cu²⁺ dimers and weaker coupling between the dimers. Singlet-triplet excitations and their dispersion are measured by single crystal INS studies with temperature and a magnetic field as variables. At low temperatures they show quantum critical phenomena. Recently we could show that TlCuCl₃ exhibits Bose-Einstein Condensation behavior in an external magnetic field, the first demonstration of this phenomenon in a magnetic insulator.