Action cross sections of two-photon excited luminescence of some Eu(III) and Tb(III) complexes.

Four different luminescent lanthanide complexes have been studied with respect to multiphoton excitation using near-infrared femtosecond pulses. The method for measuring action cross sections of two-photon excited fluorescence in solution relative to a known standard is reviewed. Two refractive index-related corrections are necessary in this method: one for the multiphoton excitation process, the other for the collection of the emitted light. It has been found that (2,4,6-trimethoxyphenyl)dipicolinic acid and Michler's ketone are reasonable sensitisers of two-photon excited lanthanide luminescence in solution, whereas dipicolinic acid and carbostyril-124 do not give rise to any detectable two-photon excited lanthanide luminescence using modest excitation powers (<20 mW focused at the sample) in the 700-1000 nm range.