<s>
Stokes	B-Algorithm
shift	I-Algorithm
is	O
the	O
difference	O
(	O
in	O
energy	O
,	O
wavenumber	O
or	O
frequency	O
units	O
)	O
between	O
positions	O
of	O
the	O
band	O
maxima	O
of	O
the	O
absorption	O
and	O
emission	O
spectra	O
(	O
fluorescence	O
and	O
Raman	B-Algorithm
being	O
two	O
examples	O
)	O
of	O
the	O
same	O
electronic	O
transition	O
.	O
</s>
<s>
Sometimes	O
Stokes	B-Algorithm
shifts	I-Algorithm
are	O
given	O
in	O
wavelength	O
units	O
,	O
but	O
this	O
is	O
less	O
meaningful	O
than	O
energy	O
,	O
wavenumber	O
or	O
frequency	O
units	O
because	O
it	O
depends	O
on	O
the	O
absorption	O
wavelength	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
50	O
nm	O
Stokes	B-Algorithm
shift	I-Algorithm
from	O
absorption	O
at	O
300	O
nm	O
is	O
larger	O
in	O
terms	O
of	O
energy	O
than	O
a	O
50	O
nm	O
Stokes	B-Algorithm
shift	I-Algorithm
from	O
absorption	O
at	O
600	O
nm	O
.	O
</s>
<s>
When	O
a	O
system	O
(	O
be	O
it	O
a	O
molecule	O
or	O
atom	B-Language
)	O
absorbs	O
a	O
photon	B-Application
,	O
it	O
gains	O
energy	O
and	O
enters	O
an	O
excited	O
state	O
.	O
</s>
<s>
One	O
way	O
for	O
the	O
system	O
to	O
relax	O
is	O
to	O
emit	O
a	O
photon	B-Application
,	O
thus	O
losing	O
its	O
energy	O
(	O
another	O
method	O
would	O
be	O
the	O
loss	O
of	O
energy	O
as	O
translational	O
mode	O
energy	O
via	O
vibrational-translational	O
or	O
electronic-translational	O
collisional	O
processes	O
with	O
other	O
atoms	O
or	O
molecules	O
)	O
.	O
</s>
<s>
When	O
the	O
emitted	O
photon	B-Application
has	O
less	O
energy	O
than	O
the	O
absorbed	O
photon	B-Application
,	O
this	O
energy	O
difference	O
is	O
the	O
Stokes	B-Algorithm
shift	I-Algorithm
.	O
</s>
<s>
The	O
Stokes	B-Algorithm
shift	I-Algorithm
is	O
primarily	O
the	O
result	O
of	O
two	O
phenomena	O
:	O
vibrational	O
relaxation	O
or	O
dissipation	O
and	O
solvent	O
reorganization	O
.	O
</s>
<s>
Stokes	O
fluorescence	O
is	O
the	O
emission	O
of	O
a	O
longer-wavelength	O
photon	B-Application
(	O
lower	O
frequency	O
or	O
energy	O
)	O
by	O
a	O
molecule	O
that	O
has	O
absorbed	O
a	O
photon	B-Application
of	O
shorter	O
wavelength	O
(	O
higher	O
frequency	O
or	O
energy	O
)	O
.	O
</s>
<s>
If	O
the	O
emitted	O
photon	B-Application
has	O
more	O
energy	O
than	O
the	O
absorbed	O
photon	B-Application
,	O
the	O
energy	O
difference	O
is	O
called	O
an	O
anti-Stokes	O
shift	O
;	O
this	O
extra	O
energy	O
comes	O
from	O
dissipation	O
of	O
thermal	O
phonons	B-Language
in	O
a	O
crystal	O
lattice	O
,	O
cooling	O
the	O
crystal	O
in	O
the	O
process	O
.	O
</s>
<s>
Photon	B-Application
upconversion	O
is	O
another	O
anti-Stokes	O
process	O
.	O
</s>
<s>
It	O
is	O
more	O
commonly	O
observed	O
in	O
Raman	B-Algorithm
spectroscopy	I-Algorithm
,	O
where	O
it	O
can	O
be	O
used	O
to	O
determine	O
the	O
temperature	O
of	O
a	O
material	O
.	O
</s>
