Gilchrist and Reynolds
184
5.4.19 Correcting Emission Signal Channels
The spectral correction of the emission channel is necessary to provide the “true” emission
spectrum of the sample because both the analyzing monochromator and detector each have
a spectral response. The normal situation is to measure this correction function once and
store the result in a file for use during a measurement. The correction file is measured using
a calibrated tungsten source operated under very strict constant current conditions (often
in conjunction with a calibrated deuterium source for UV correction). The tungsten source
has a spectral emission file that corresponds to the light intensity at a certain distance from
the source. The International Commission on Illumination (CIE) is responsible for publishing technical data of all the well known standard illuminants. The CIE publishes relative
spectral power distribution data of such illuminants, and for a tungsten-filament source
the data will cover 380 nm to 780 nm in increments of 5 nm (www.cie.co.at). However,
because the emission spectrum is smooth, interpolating this data to provide higher resolution data is possible.
The spectral power distribution of the tungsten lamp is used to generate a spectral emission file, W lamp
_
λ
( ). If the measured signal through the emission channel is Em Sig
−
( )
λ ,
then the correction file Em Cor
−
( )
λ = Em Sig
−
( )
λ / W lamp
_
λ
( ). Note that the spectral
emission file is usually normalized (from 0 to 1). Thus the corrected emission signal is
equal to Em Sig
−
( )
λ / Em Cor
−
( ).
λ
5.4.20 Quantum Yield
The quantum yield (QY) is a fundamental property of a luminescent sample. Specifically,
it refers to the ratio of the number of photons of light radiated from the photoluminescent
material to the number of photons of light that the material absorbs. Practically, QYs are
important as they allow the quantitative assessment of fluorescence from materials and the
effects of interferences on the fluorescence properties. Such measurements can be made on
420
0
1.0
1.0
0.5
0
UNCORRECTED
EXCITATION
CORRECTED
EXCITATION
ABSORPTION
EMISSION
FLUORSCEIN IN 0.05 N NaOH
FLUORESCENCE
INTENSITY (RELATIVE)
ABSORBANCE
520
500
480
WAVELENGTH (nm)
460
540
560
580
440
Figure 5.21. Example of corrected and uncorrected excitation spectra.
184
5.4.19 Correcting Emission Signal Channels
The spectral correction of the emission channel is necessary to provide the “true” emission
spectrum of the sample because both the analyzing monochromator and detector each have
a spectral response. The normal situation is to measure this correction function once and
store the result in a file for use during a measurement. The correction file is measured using
a calibrated tungsten source operated under very strict constant current conditions (often
in conjunction with a calibrated deuterium source for UV correction). The tungsten source
has a spectral emission file that corresponds to the light intensity at a certain distance from
the source. The International Commission on Illumination (CIE) is responsible for publishing technical data of all the well known standard illuminants. The CIE publishes relative
spectral power distribution data of such illuminants, and for a tungsten-filament source
the data will cover 380 nm to 780 nm in increments of 5 nm (www.cie.co.at). However,
because the emission spectrum is smooth, interpolating this data to provide higher resolution data is possible.
The spectral power distribution of the tungsten lamp is used to generate a spectral emission file, W lamp
_
λ
( ). If the measured signal through the emission channel is Em Sig
−
( )
λ ,
then the correction file Em Cor
−
( )
λ = Em Sig
−
( )
λ / W lamp
_
λ
( ). Note that the spectral
emission file is usually normalized (from 0 to 1). Thus the corrected emission signal is
equal to Em Sig
−
( )
λ / Em Cor
−
( ).
λ
5.4.20 Quantum Yield
The quantum yield (QY) is a fundamental property of a luminescent sample. Specifically,
it refers to the ratio of the number of photons of light radiated from the photoluminescent
material to the number of photons of light that the material absorbs. Practically, QYs are
important as they allow the quantitative assessment of fluorescence from materials and the
effects of interferences on the fluorescence properties. Such measurements can be made on
420
0
1.0
1.0
0.5
0
UNCORRECTED
EXCITATION
CORRECTED
EXCITATION
ABSORPTION
EMISSION
FLUORSCEIN IN 0.05 N NaOH
FLUORESCENCE
INTENSITY (RELATIVE)
ABSORBANCE
520
500
480
WAVELENGTH (nm)
460
540
560
580
440
Figure 5.21. Example of corrected and uncorrected excitation spectra.