Several situations can produce multiple peaks in fluorescence
emission spectra. One is the transition from the lowest excited state
to different vibrational levels of the ground electronic state. Another
is the transition from different excited electronic states to the ground
state. In most cases, the former is dominant because the rate of
internal conversion is very fast (10- 1 2 s). Also, if more than one
component exists in the sample, multiple emission peaks can be
attributed to tiem.