| abstract |
The invention relates to an ink composition containing (a) a compound of formula I Lm-Ln3+(Ch-)n (I), wherein Ln represents a lanthanide, Ch- is a negatively charged ligand containing at least one UV absorbing double bond, n denotes 3 or 4, m denotes a number from 1 to 4, in case n is 3, m denotes a number from 1 to 4 and L is a neutral monodentate or polydentate nitrogen-, oxygen- or sulfur-containing UV absorbing ligand with the exception of 2,2'-bipyridyl or, in case n is 4, m denotes 1 and L is a single-charged cation; and (b)a liquid ink carrier, which can be used for applying hidden mark on objects which can only be revealed under UV exposure. |