Different preparation methods are employed to obtain single crystals (crystal growth in solution, in silica gels, or by the Bridgman technique), crystalline and nanostructured materials (from solution or by hydrothermal synthesis) and glasses (from oxidic melts or by the modern Sol-Gel process). Using different experimental spectroscopic and magnetic techniques, the co-ordination behaviour of the paramagnetic centres is investigated. The information obtained includes, for example, the symmetry and distortion of the co-ordination polyhedra, degree and type of metal-ligand interaction, evidence of exchange and/or superexchange interactions between neighbouring centres. The interpretation involves application of
symmetry and group theoretical methods, semi-empirical models (e.g., based on crystal field theory), determination of crystal field and intensity (Judd-Ofelt) parameters, and magnetic exchange coupling constants.