Non-linear luminescence of dimethylaminobenzylidene-I,3-indandione solids

The origin of the non-linear anti-Stokes luminescence effect in dimethylaminobenzylidene-1,3-indandione (DMABI) crystals, i.e. the luminescence in the visible spectral region created by infrared excitation, was investigated by means of ultrafast pump-probe and luminescence spectroscopy. In contrast with the previously proposed luminescence excitation model based on low-energy exciton annihilation, the luminescence state 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 luminescence are discussed. Exciton-exciton annihilation on the manifold of luminescent states was observed at high excitation intensities.