Guy Cox wrote:
>
> >> >It also does what M Serrano calls upconvert - emit at lower wavelength than
> >> >excite and is not a 2 photon event
> >> >
> >> >Ex 633  Em 580
> >> >
> >>
> >>
> >> And it IS really a two-photon event - it just doesn't behave like one.
> >> (It shows 1-photon kinetics and doesn't require huge light fluxes but
> >> two photons are absorbed to generate one photon of fluorescence.)
> >>
> >Is it a 2-photon effect, or is it a Raman effect (photon+vibration-mode)
> >if it is
> >a Raman effect, it will dissappear at low temperatures since it would be
> >anti-stokes
> >(that is, it requires an existing vibration mode to provide the
> >additional energy).
>
> I'll have to check this with Scott Kable, who is the chemist of the
> team that did this work, but as I recall the molecule has a 'stable'
> triplet state which is very easy to create with a one-photon event.
> Absorption of a second photon then converts this to the normal excited
> state from which fluorescence emission occurs with normal de-excitation.
> Since the excitation of the triplet state has a high probability there
> is always a pool of 'triplet state' molecules present, so it is only
> the kinetics of the second excitation which determine fluorescence
> emission.
>
If the second radiative transition is from a triplet state, it should be
a triplet-triplet
transition. If so, then the decay to ground state would be a
triplet-singlet transition. Since this is "forbidden", it should have a
long time constant and appear more like phosphorescence.

Do you have a reference that describes this behavior?

--aryeh
--
Aryeh Weiss                          | email: [log in to unmask]
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