I have measured DRS spectra of DPA (9,10-diphenylanthracene) solid powder from 300 to 800 nm. What puzzles me is that its absorption value begins to decrease when the wavelength is less than 440 nm and quickly drops below zero (-0.35). In theory, its absorption should begin to increase when the wavelength is less than 440 nm.
@Paul Milham Thanks for your participation. Yes, the DPA solid powder strongly emits fluorescence in the region of 385-550 nm under UV (300~440 nm) irradiation.
My first reaction is to say check your baseline, but the point of Paul Milham is important. Any fluorescence should be red shifted from the absorption. You therefore need to consider how you are making your measurement. If your wavelength selection is before your sample, then the detector could be picking up longer wavelength fluorescence. If your wavelength selection is after the sample, then you should not.
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