A tetramethylammonium-saponite-1,4-dihydroxyanthraquinone intercalation compound was prepared and a persistent spectral zero-phonon hole was obtained at liquid helium temperatures by Kr+ laser light irradiation (520.8 nm). This is the first example of persistent hole formation of 1,4-dihydroxyanthraquinone in crystalline inorganic matrices. In spite of the high concentration of 1,4-dihydroxyanthraquinone (ca. 1.5 mol kg-1), a narrow hole with the initial width of 0.25 cm-1 (4.6 K) was obtained with no distinct decrease in burning efficiency (>1.0 × 10-4) if compared with those doped in ordinary polar polymers or organic glasses. The microscopic geometry of the compound is discussed on the basis of hole formation properties as well as X-ray powder diffraction and 13C NMR observation.
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