A STUDY OF OPTICAL-ABSORPTION IN 9,10-ANTHRAQUINONE CRYSTALS

Single crystals of 9,10-anthraquinone having dimensions 5 mm x 5 mm x 1.5 mm were grown from the melt using the Bridgeman technique. The starting material was purified by sublimation and zone-refining techniques in specially designed crystal-growth tubes. The crystals were transparent and yellow in colour, and could be cleaved easily along ab-, bc-planes and poorly along the ac-planes of the crystal. Thin layer chromatography of the final crystals was performed, and no impurity was detected in these crystals by this technique. The cleaved crystals were found to have a surface photocurrent of approximately 10(-11) A, which increased non-linearly with the increasing voltage at room temperature. This is attributed to the formation of triplets in the bulk of the crystal which migrate and dissociate at the surface of the crystal. The optical absorption spectrum in benzene and ether solutions were found to exhibit similar behaviour in the visible range, i.e. 320-450 nm. From the optical absorbance data, the optical band gap was found to be approximately 3.4 eV.