The action spectra for fading of Rhodamine B (C.I. 45170) are similar for irradiations in aqueous solution and on wool, bleached wool and nylon fabrics, suggesting that the mechanisms of fading are similar in all cases and that the fiber plays no significant photosensitizing role. In solution, the quantum yield for photodegradation varies markedly with the wavelength of the incident radiation, ranging from 1.1 × 10-6 mols/einstein at 540-560 nm to 8.4 × 10-6 mols/einstein at 325-345 nm. On the basis of the results presented, it is calculated that visible radiation (400-600 nm) is responsible for approximately 80% of the fading when Rhodamine B dyed wool is exposed to sunlight.
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