When the waves are moving away from the light beam, the largest signal is observed in retroreflection and the Stokes shift
moves to longer wavelengths, as in stimulated Raman scattering.
Well-defined relationships have been established showing a well-defined relationship with the vibrational coherence and the luminescence yield with Stokes shift
, integrated Raman intensity, and electronic gap [15-18].
, absorption and emission spectral data and fluorescence lifetime of studied compounds in DMSO, [DMSO.sub.80%]/ [THF.sub.20%], [DMSO.sub.60%]/[THF.sub.40%], [DMSO.sub.40%]/ [THF.sub.60%], [DMSO.sub.20%]/[THF.sub.80%] and THF.
The blue light passing through the phosphor experiences the Stokes shift
down conversion and appears as white light.
Maximum emission wavelength along with full width at half maximum (fwhm) and the Stokes shift
values of the polyoxadiazoles I and copolyoxadiazoles II are collected in Table 1.
Tables 1 and 2 summarize the basic photophysical characteristics of MDs--absorption ([[lambda].sub.A]) and fluorescence ([[lambda].sub.f]) maxima, Stokes shift
([v.sub.A] - [v.sub.F]), oscillator strength (f), quantum yield of fluorescence ([[PHI].sub.f]), and energetic yield of fluorescence ([E.sub.f]).
However, they have a very small Stokes shift
(Goze et al.
Besides, the FL and UV-vis absorption spectra are extremely sharp with a full width of half maximum (FWHM) about 25 nm and the stokes shift
about 10 nm.
In ordinary organic fluorophores (e.g., fluorescein, quinine, rhodamine, etc.), which are also dye chromophores, the color changes upon exposure to ultraviolet or to visible light and the corresponding Stokes shift
is relatively short, of the order of few tens of nanometers.
The difference in the wavelengths of maximum absorption and maximum emission is called the Stokes shift
. Fluorescein has a relatively small Stokes shift
of approximately 20 nm, and as can be seen in Fig.
Figure 4 show the variation of Stokes shift
([DELTA][nu]) with solvent polarity function [DELTA]f([epsilon],n).
Finally, the Stokes shift
of the synthesized phosphor was calculated to be 7086 [cm.sup.-1] using the excitation band at 290 nm and the emission band at 365 nm.