Horiba Scientific Quanta-phi F-3029, Руководство по эксплуатации

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Quanta-
φ
rev. C (23 Apr 2010) Theory of Operation
1-3
Photoluminescence quantum yield
An important use of the integrating sphere in conjunction with your spectrofluorometer
is the determination of a sample’s photoluminescence quantum yield. The photolumi-
nescence quantum yield for a particular molecular species is determined by the first-
order rate processes that compete for the excitation energy. The three main processes
can be defined with first-order rate constants, such as
k
F
, the rate constant of fluores-
cence decay (in units of s
–1
), k
NR
, the rate constant of nonradiative decay, and k
T
, the
rate constant of photochemical energy transfer. Using these three rate constants, the
fluorescence quantum yield
φ
is defined as
The fluorescence quantum yield is directly related to the fluorescence lifetime
τ :
Any increase in the nonradiative decay processes (
k
NR
) related to events such as
quenching and thermal dissipation or energy-transfer ( k
T
) processes—including Förster
Resonance Energy Transfer (FRET)—will decrease both the quantum yield
φ
and fluo-
rescence lifetime
τ
. Likewise any decrease in k
NR
or k
T
will increase
φ
and
τ
.
The multiple randomized, diffused reflections in the integrating sphere eliminate
any isotropic (directional) features of the sample emission from the excited molecular
species. Hence, measurement of polarization is not possible within an integrating
sphere.
Following is a brief description of the theory and recommended procedure for measur-
ing quantum yield using the Quanta-
φ
integrating sphere.
General approach
For a general approach, not requiring an integrating sphere, see Joseph R. Lakowicz’s
book,
Principles of Fluorescence Spectroscopy .
1
Theory
The sample is placed in the integrating sphere, and excited with a monochromatic
source of wavelength
λ
. The film absorbance, A , is
b
c b
L
L L
A


(7)
1
Joseph R. Lakowicz, Principles of Fluorescence Spectroscopy , 3
rd
ed., New York, Springer, 2006, pp.
8–10, 54–55.