The wavelength variation of fluorescent intensity has been plotted
for excitation and emission spectra for all the mixtures and shown in
Fig. 6(a) and (b). From this figure we see that there is non-linear behavior
of fluorescent intensity. The excitation wavelength for pure FLC is
336 nm, fluorescent dye is 266 nm while it decreases for mixture 1
and mixture 3 i.e. 319.5 nm and 326.6 nm respectively. But for mixture
2 it increases in comparison to the all mixtures. The figure of emission
spectra for all the mixtures shows the same trend as for excitation
spectra i.e. highest for mixture 2 in comparison to all the mixtures.
The shifting peak in the emission spectra for the mixture 2 i.e. 3% doping
of fluorescent dye in pure FLC is due to energy associated with fluorescence
emission transitions which is typically less than that of absorption.
Therefore, the resulting emitted photons have lesser energy and
are shifted to longer wavelengths. This phenomenon occurs as commonly
employed in solution investigations. This is due to the rapid
decay of excited electrons to the lowest vibrational energy level of excited
state. In addition, fluorescence emission is usually accompanied by
transitions to higher vibrational energy levels of the ground state,
resulting in further loss of excitation energy to thermal equilibration
of the excess vibrational energy. Other events, such as solvent orientation
effects, excited-state reactions, complex formation, and resonance
energy transfer can also contribute to longer emission wavelengths.
We have also evaluated quantum yield with the help of Elico software
using excitation and emission data for all the mixtures.