NONLINEAR LUMINESCENCE OF DIMETHYLAMINOBENZYLIDENE-1,3-INDANDIONE SOLIDS

The origin of the non-linear anti-Stokes luminescence effect in dimeth ylaminobenzylidene-1,3-indandione (DMABI) crystals, i.e. the luminesce nce in the visible spectral region created by infrared excitation, was investigated by means of ultrafast pump-probe and luminescence spectr oscopy. In contrast with the previously proposed luminescence excitati on model based on low-energy exciton annihilation, the luminescence st ate was found to be excited via two-photon absorption through virtual and real (characterised by 1 ps lifetime) intermediate states. Second- harmonic generation and pulse duration effects on the non-linear lumin escence are discussed. Exciton-exciton annihilation on the manifold of luminescent states was observed at high excitation intensities.