Geoscience Reference
In-Depth Information
The unabsorbed part is determined by measurement 2 and hence
Y
=
( )
+
1
ALBPB
.
The directly absorbed light is re-emitted by the sample and hence
X
=η
ALA
, where
η
is
called the quantum efficiency. Thus,
LC P
+= +
( )
+
-(
)
η
ALAALB P
1 . Therefore the
photoluminescence quantum efficiency,
η
, can be expressed as shown in
Eq. (5.14)
:
-(
)
PC
−−
APB
ALA
(
1
)
η=
(5.14)
LC
LB
where
A
=−
1
Because the spectral features are measured the values of
PC
,
PB
,
LC
,
LB
, and LA can
be substituted from the integration analysis of the curves of measurements 1, 2, and 3. This
means that the quantum efficiency can be expressed as: (5.15)
P
31
−−
(
A P
)
2
η=
(5.15)
AL
1
L
L
3
2
where
A
=−
1
5.4.22 Fluorescence Units - What Are They?
Fluorescence units are often a term used to describe the intensity axis of the spectral plot
(Resch-Genger,
2007
). In reality, there appears to be no “standard” definition of this term,
nor any means to quantify it in an absolute radiometric meaning. There are so many effects,
such as optical, sample, and instrumentation related, involved in fluorescence measure-
ments that without a full and strict radiometric calibration fluorescence units are no more
than some
arbitrary
scale of intensity. Fluorescence units are therefore not directly compa-
rable from instrument to instrument or from laboratory to laboratory. The situation becomes
even more complex when thinking about excitation-emission matrices (EEMs) as the spec-
tral position in excitation-emission space can be dramatically affected by the spectral cor-
rection used in both channels as well as the possibilities of signal saturations. These are
important considerations to understand when reporting any fluorescence intensity data.
References
Arecchi, A.V., Messadi, T., and Koshel, R.J. (2007).
Field Guide to Illumination
.
Bellingham, WA: SPIE Press,
Fery-Forgues, S. and Lavabre, D. (1999, September). Are fluorescence quantum yields
so tricky to measure? A demonstration using familiar stationery products.
J. Chem.
Educ
.,
76
(9), 1260-1264.
