Discuss the instrumental setup for the experimental determination of quantum yield.
Answers
Experimental set-up for the determination of the luminescence quantum yield.
The inset represents the collected solid angle and emphasizes the role of the solvent index.
The excitation wavelength (440 nm) is selected (with a 10 nm bandwidth) from a 450 W Xenon lamp
and a monochromator (Fluorolog-3). The beam is slightly focused (with an 8◦
angle) on a 10 mm quartz
cuvette (Hellma, 111QS). In this report, all the experiments are done at room temperature.
This experimental setup provides in a single spectrum both the transmission and the emission from
the samples. Therefore, errors on the position of the cuvette, the fiber and the filter are less critical. The
transmitted and emitted lights from the sample are collected by an optical fiber located at 40 mm from
the cuvette, on the opposite side of the excitation, with a 3 mm diameter. The collected angle is then
4 × 10−3
. The collected light is analyzed with a Jobin-Yvon Spectrometer HR460 and a nitrogen-cooled
Si Charged-Coupled Device (CCD) detector [23].
A typical spectrum for a rhodamine 101 solution is presented in Figure 2. The peak at 440 nm
corresponds to the transmitted light through the cuvette whereas the part of the spectrum centred at
600 nm is the fluorescence of the rhodamine 101. Assuming isotropic emission, about 0.02% of the
emission is collected by our fiber. On the other hand, about 2% of the transmitted beam is collected.
The latter component is thus much more intense. In order to be able to measure both components in the
same acquisition, we have introduced a filter which strongly decreases the transmitted component while
preserving the whole emission component. For the experiments presented in this paper, a high pass filter
with a cut-off at 520 nm (KV520 Schott filter) is used. Its transmission at 440 nm is 3 × 10−5
.
When the emission spectrum is broad, or when the reference emission is not exactly at the same
wavelength as the sample emission, the spectral response of the system must be taken into account. It
includes the effects of the KV520 filter, the optical fiber, the monochromator and the CCD detector.
We determined the spectral response of our setup by using a calibrated tungsten lamp (Figure 2). For
calculating the integrated emission intensity IF , we will always use corrected emission spectra.
