Gilchrist and Reynolds
186
5.4.21 Measuring Quantum Yields: The Three-Measurement Technique
The three-measurement technique (Figure 5.22) is one of several methods of measuring the
quantum yield of a sample. When used with an integrating sphere (IS) it is a method that
provides compensation for the reabsorption effects in the measurements.
Measurement 1: Excitation Power – NO sample is in the IS.
No sample is present in the
•
IS.
The excitation monochromator is set to the excitation wavelength.
•
Emission scan across spectral range including the excitation peak.
•
Determine the peak wavelength from the measurement.
•
Correct the spectrum for the integration period to give the number of photons per second.
•
Integrate the spectrum from the background (zero level) before the peak to the same
•
background after the peak to give the total number of photons per second in the wavelength range of the peak, and therefore available to the sample L1.
Store the spectrum and the integrated photons per second signal rate.
•
Measurement 2: Re-Absorption Signal – Sample is present in the IS.
Place the sample into the IS but in the OFF position, such that it is not directly illumi•
nated by the excitation light.
Excitation monochromator is set to the excitation wavelength.
•
Emission scan across the spectral range, including the excitation peak.
•
Determine the peak wavelength from the measurement.
•
Correct the spectrum for the integration period to give the number of photons per second.
•
Integrate two regions of the spectrum:
•
The excitation spectrum from the back ground (zero level) before the peak to the same
•
background after the peak to give the total number of photons per second in the wavelength range of the peak, and therefore the number of excitation photons that are not
reabsorbed by the sample. L2
The PL emission spectrum from the background (zero level) before the peak to the
•
same background after the peak to give the total number of photons per second in the
wavelength range of the peak, and therefore the number of emission photons that are
emitted by the sample. P2
Store the spectrum and the two integrated photons per second signal rates,
•
L2 and P2.
Measurement 3, Reabsorption Signal – Sample is present in the IS.
Place the sample into the IS but in the ON position such that it is directly illuminated by
•
the excitation light.
Excitation monochromator is set to the excitation wavelength.
•
Emission scan across the spectral range, including the excitation peak.
•
Determine the peak wavelength from the measurement.
•
Correct the spectrum for the integration period to give the number of photons per
•
second.
186
5.4.21 Measuring Quantum Yields: The Three-Measurement Technique
The three-measurement technique (Figure 5.22) is one of several methods of measuring the
quantum yield of a sample. When used with an integrating sphere (IS) it is a method that
provides compensation for the reabsorption effects in the measurements.
Measurement 1: Excitation Power – NO sample is in the IS.
No sample is present in the
•
IS.
The excitation monochromator is set to the excitation wavelength.
•
Emission scan across spectral range including the excitation peak.
•
Determine the peak wavelength from the measurement.
•
Correct the spectrum for the integration period to give the number of photons per second.
•
Integrate the spectrum from the background (zero level) before the peak to the same
•
background after the peak to give the total number of photons per second in the wavelength range of the peak, and therefore available to the sample L1.
Store the spectrum and the integrated photons per second signal rate.
•
Measurement 2: Re-Absorption Signal – Sample is present in the IS.
Place the sample into the IS but in the OFF position, such that it is not directly illumi•
nated by the excitation light.
Excitation monochromator is set to the excitation wavelength.
•
Emission scan across the spectral range, including the excitation peak.
•
Determine the peak wavelength from the measurement.
•
Correct the spectrum for the integration period to give the number of photons per second.
•
Integrate two regions of the spectrum:
•
The excitation spectrum from the back ground (zero level) before the peak to the same
•
background after the peak to give the total number of photons per second in the wavelength range of the peak, and therefore the number of excitation photons that are not
reabsorbed by the sample. L2
The PL emission spectrum from the background (zero level) before the peak to the
•
same background after the peak to give the total number of photons per second in the
wavelength range of the peak, and therefore the number of emission photons that are
emitted by the sample. P2
Store the spectrum and the two integrated photons per second signal rates,
•
L2 and P2.
Measurement 3, Reabsorption Signal – Sample is present in the IS.
Place the sample into the IS but in the ON position such that it is directly illuminated by
•
the excitation light.
Excitation monochromator is set to the excitation wavelength.
•
Emission scan across the spectral range, including the excitation peak.
•
Determine the peak wavelength from the measurement.
•
Correct the spectrum for the integration period to give the number of photons per
•
second.