Photo-Fluorescence Decay Times of Organic Phosphors
A method for measuring photo-fluorescence decay times to approximately 10-9 sec is described. Observations are made of the phase and modulation of the light from a 7·5 Mc/s air discharge tube, and of the fluorescence excited by this light, using a photomultiplier modulated at 15 Mc/s. The decay times of anthracene, stilbene, terphenyl and diphenylacetylene crystals of various thicknesses have been measured. Due to the overlap of the emission and absorption spectra, the technical decay time of a thick crystal is greater than the molecular decay time (t f )0 observed for a microcrystalline specimen. For anthracene t f = 14 ± 2 mμsec and (t f )0 = 3-5 + 1-0 m/xsec. This value of t f agrees with that derived from (t f )0 and the comparative technical and molecular emission spectra. For each of the compounds studied the molecular decay time (t f ),00 in the absence of internal quenching, is of the order of 3–4 mμsec.
KeywordsQuartz Benzene Tungsten Polystyrene Naphthalene
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