Phosphorimeter factor

Once the efficiency of normal fluorescence had been determined, the efficiencies of phosphorescence and delayed fluorescence under the same conditions were derived without reference to any other solution. The ratio of the efficiencies of delayed fluorescence (6) to that of normal fluorescence was simply caculated by comparing the intensities at one of the principal maxima in the spectra, which were, of course, identical in shape. Due correction was made for the phosphorimeter factor (assumed to be 3 for lifetimes greater than 1 msec.) and also for the different instrumental sensitivities at which the two spectra were measured. Phosphorescence efficiencies were determined in a similar manner, except that the spectra first had to be corrected and the areas under the corrected curves compared with those of the corresponding normal fluorescence spectra. The phosphorimeter and instrumental sensitivity factors were then applied as before. 

Typical normal and delayed emission spectra from 5 X 10anthracene in ethanol are shown in Figure 17.38 Similar results were obtained in cyclohexane. The observed intensity of the delayed fluorescence band was about 0.28% of that of the normal fluorescence band and thus, applying the phosphorimeter factor of 3, the efficiency (6) of delayed fluorescence in this solution was approximately 0.8% of the efficiency (f) of normal fluorescence. In solutions with lower concentrations of anthracene the value of 6 was proportionately lower (see Table IV). 

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