Temperature dependence of photoluminescence properties of CdSe
quantum dots
Tetsuya Kuwabara, DaeGwi Kim*, and Masaaki Nakayama
Department of Applied Physics, Osaka City University, 3-3-138, Sugimoto, Sumiyoshi-ku, Osaka, 558-8585
* corresponding author e-mail: tegi@a-phys.eng.osaka-cu.ac.jp
References
1. S. L. Cumberland et al., Chem. Mater. 14, 1576 (2002).
2. 2. D. Kim et al., Physica E, 21, 363 (2004).
PL Intensity (arb. units)
Intensity (arb. units)
In the past decades, semiconductor quantum dots (QDs) have attracted considerable
attention to understand the size dependence of their physical and/or chemical properties.
Since optical properties of the QDs depend on the size, the preparation of the QDs with a
narrow size distribution is essential in studies of QDs. So far, various synthetic
techniques to prepare mono-disperse and highly crystalline QDs have been developed,
especially for CdSe QDs. However, QDs dispersed in solutions were major targets in
most of the studies. Thus, little attention has been paid to the temperature dependence of
the photoluminescence (PL) properties of CdSe QDs. In the present work, we have
investigated the temperature dependence of exciton dynamics in CdSe QDs dispersed in
polymer films. CdSe QDs with a radius of 1.9 nm were prepared by a standard
lyothermal method using a single source precursor [1]. We dispersed CdSe QDs into
polystyrene films to measure the temperature dependence of absorption, PL, and PLdecay profiles.
Figure 1(a) shows the temperature dependence of the absorption and PL spectra
for CdSe QDs. The absorption- and PL-peak energies shift
(a) CdSe QDs
Absorption
to the higher energy side and the spectral widths decrease
10 K
with a decrease in temperature. We note that the
PL
preparation of QDs with the narrow size distribution
50 K
1.2
enables us to observe the clear temperature dependence of
100 K
1.4
the spectral profiles. It is noted that the rate of the thermal
150 K
1.5
quenching is very small: The PL intensity at 300 K is 46 %
of that at 10 K. Figure 1(b) shows temporal profiles of the
200 K
1.9
band-edge emission at 10, 50, 100, and 150 K, respectively.
250 K
2.5
The decay profiles become slightly slower as the
300 K
3.2
temperature is increased in a temperature region between
1.6
2.0
2.4
2.8
10 and 180 K. The temperature dependence of the profiles
Photon Energy (eV)
can be explained in terms of a three-level model: a ground
(b)
state and two excited states of a lower-lying bound-exciton
state and a higher-lying free-exciton state with a triplet
150 K
origin (the so-called dark-exciton state). The quantitative
analysis based on the three-level model will be discussed
100 K
in detail.
50 K
10 K
0
Fig.1
0.5
1.0
Time (s)
1.5