Photorefractive effects from light-induced charge separation and a refractive index change by means of the electro-optic effect have been found in a large number of inorganic crystals. Recently we have reported first observations of such an effect in an organic material.1 In our experiments, we have doped single crystals of the electro-optic organic material 2-cydo-octylamino-5-nitropyridine (COANP) with 7,7,8,8-tetra-cyanoquinodimethane (TCNQ). TCNQ is a strong electron acceptor, known to form charge transfer complexes with a large number of organic molecules. TCNQ-doped crystals of COANP show a typical absorption band at wavelengths ~650 nm, which could be assigned to such a charge transfer complex. Figure 1 shows the absorption coefficients of a doped and an undoped COANP crystal. The doped crystals were grown from an undercooled melt containing 0.1 wt: % TCNQ.

© 1991 Optical Society of America

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