Organometallic complexes comprising a trivalent lanthanide metal ion complexed with one or more polydentate ligands containing one or more pyrazolyl-derived groups, such as trispyrazolyl borate species, are useful in light emitting materials e.g., in electroluminescent flat panel displays. In the complexes, several classes of which are novel, a coordinate bond is formed between the metal and one of the nitrogen atoms of the pyrazolyl rings.