Experimental Determination of the Absorption Cross-Section and
Molar Extinction Coefficient of Colloidal CdSe Nanoplatelets
Aydan Yeltik, 1 Savas Delikanli, 1 Murat Olutas, 1,2 Yusuf Kelestemur, 1 Burak Guzelturk, 1,3
and Hilmi Volkan Demir 1,3*
1
Department of Physics, Department of Electrical and Electronics Engineering, UNAM –
Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800,
Turkey
2
3
Department of Physics, Abant Izzet Baysal University, Bolu 14280, Turkey
Luminous! Center of Excellence for Semiconductor Lighting and Displays, School of
Electrical and Electronic Engineering, School of Physical and Materials Sciences, Nanyang
Technological University, Singapore 639798, Singapore
(a)
Wavelength (nm)
620
UV-Vis absorbance
1.0
0.8
558
496
434
372
310
3.6
4.0
host medium
NPL sample as synthesized
NPL sample after cleaning
0.6
0.4
0.2
0.0
2.0
2.4
2.8
3.2
Energy (eV)
1
Figure S1. UV-Vis absorbance spectra of the reaction host medium solution containing cadmium
acetate, oleic acid and octadecene, reaction mixture and final mixture after the extraction process of
the NPLs.
Table S1. Corresponding ε values of 4 ML and 5 ML thick CdSe NPLs at the energy of hh-e peak
and at the high energy value 3.1 eV.
Lateral Size
2
(nm )
Lateral Size
ε for 4 ML thick NPL
-1
-1
2
(cm M )
hh-e peak
2.42 eV
high energy
3.1 eV
105.3 ± 16.4
9.92x106
7.54x106
170.1 ± 22.5
2.26x107
269.7 ± 38.6
391.9 ± 65.8
(nm )
ε for 5 ML thick NPL
(cm-1 M-1)
hh-e peak
2.24 eV
high energy
3.1 eV
57.2 ± 18.2
7.94x106
7.79x106
1.46x107
665.1 ± 129.5
7.05x107
3.76x107
3.19x107
1.99x107
938.4 ± 325.0
1.17x108
6.49x107
6.05x107
3.85x107
1836.6 ± 584.6
2.96x108
1.49x108
2962.9 ± 918.1
6.43x108
3.54x108
Inductively Coupled Plasma Mass Spectroscopy for further confirmation. To verify the
results from the ICP-OES measurements, we used another spectroscopy technique, ICP-MS.
Based on the Se and Cd concentrations obtained from ICP-MS, the absorption cross-sections
over the large absorption spectra were obtained for the same NPLs. For this purpose, the
NPL samples were diluted to reliable measurement ranges for ICP-MS. The results for the 4
ML NPLs using the ICP-MS technique are depicted in Figure S2(a) based on the Se
concentration and Figure S2(b) based on the Cd concentration. As seen from the figure, the
absorption cross-section increases with the platelet area for the whole absorption range.
The σ results extracted using both the Se and Cd ICP-MS concentrations of 4 ML NPLs are
consistent with those from the ICP-OES measurements in terms of the trend. However, due
to the dilution process, the measurable range of sizes has been limited with ICP-MS. Also in
2
the case of ICP-MS similar to ICP-OES, the absorption cross-sections from the Cd
concentrations are lower than those from the Se concentrations due to the excess Cd in the
samples. Furthermore, the absorption cross-sections at the transition energy of hh-e peak
exhibit a monotonous trend over the platelet area (Figure S2(c)) and this is strongly
correlated with the trend observed in the ICP-OES measurements.
3
Figure S2. Absorption cross-section spectra of 4 ML CdSe NPL samples with varying lateral sizes
obtained by using the (a) Se and (b) Cd concentrations from ICP-MS measurements. Lateral size
dependence of the absorption cross-section (c) at the energy of hh-e transition peak.
4
The absorption cross sections of the 5 ML NPLs obtained via the ICP-OES technique were
also confirmed by using the ICP-MS technique. The resulting absorption cross section spectra
are shown in Figure S3(a) using the Se concentration and Figure S3(b) using the Cd
concentration. It was observed that the σ values increase with the platelet area as in the
case of the ICP-OES measurements and the values from the Cd concentrations are smaller
than those from the Se concentrations as expected. Moreover, as can be seen in Figure
S3(c), the σ values at the hh-e transition peak present a monotonically increasing trend
over the lateral size, which is in good agreement with the trend observed for the ICP-OES
results of the same samples.
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Figure S3. Absorption cross-section spectra of 5 ML CdSe NPL samples with varying lateral sizes
obtained by using the (a) Se and (b) Cd concentrations from ICP-MS measurements. Lateral size
dependence of the absorption cross-section (c) at the energy of hh-e transition peak.
6
Figure S4. Lateral size dependence of the relative energy integrated absorption cross-section per
CdSe unit at the lowest energy absorption transition of (a) 4 ML and (b) 5 ML CdSe NPLs.
7