Question

Which of the following statements is true?

A.)The rate of fluorescence is higher than that for phosphorescence.

B.) In fluorescence, ?S ? 0.

C.) In phosphorescence, ?S ? 0.

D.) Fluorescence is a forbidden transition.

Answer 1

among the Given options the option <A> i.e. rate of fluroscence is higher than that of phosphorence is correct.

in case of fluorescence, transition is basically a singlet to snglet state transition i.e. there is no change of electron spin, whereas phosphorescence is a triplet to singlet transition which involves electron spin change which is actually a forbidden transition and less likely to happen,this results the longer lifetime of electron in the excited state in case of phosphorescence. hence , rate of phophorescence is less than that of fluorscence.