Abstracts Book - IMRC 2018

• SA2-O013
EFFECTS OF LIGAND EXCHANGE ON THE PHOTOLUMINESCENCE
OF COLLOIDAL CDSE QUANTUM DOTS
Sandra Alvarenga 1 , Carlos Rudamas 1
1 Universidad de El Salvador, Optical Spectroscopy Laboratory, Escuela de Física, Facultad de
Ciencias Naturales y Matemática, El Salvador.
The study of the optical properties of the quantum dots have been widely
investigated in solid state physics due to its wide applications in many fields. We
studied the optical properties of colloidal CdSe quantum dots (QDs) synthesized
by the thermal decomposition method by using optical spectroscopy. Samples
with different quantum dot sizes were treated with a washing method and a
ligand exchange process. The diameter of the QDs was calculated from the first
absorption peak and was estimated to be 3.29, 3.61 and 3.71 nm before ligand
exchange. During the exchange process, Formic acid was added as capping
ligand to displace Trioctylphosphine (TOP) and Oleic acid (OA) ligands on the
surface of the QDs. Photoluminescence (PL) spectra were taken before and after
the treatment. When Formic acid was added the PL spectra showed a temporary
quenching of the band edge emission. The temporary quenching could be
related to different adsorption and desorption processes on the surface of the
QDs during the ligand exchange. After several hours the quenching disappeared
and the band edge was observed again with a lower intensity with respect to the
TOP/OA capped QD spectra. Accordingly, we observed a decreasing quantum
yield (QY) of about a factor 6 to 8 for the investigated samples, when formic acid
was added. The change in the QY could be related to nonradiative states that
have been enhanced with the presence of Formic acid on the QDs surface due
to underpassivation. The Full Width at Half Maximum (FWHM) had a small
variation after the ligand exchange (~4.61 nm). This variation represents a ~13%
of the original FWHM calculated from the PL spectra of TOP/OA capped QDs.
The comparison of the FWHM suggests that the monodispersity of the
nanostructures suffered only a small change after the exchange process.
Acknowledgment:
The authors would like to thank the members of the research group that
contributed to the discussion of these results. This work has been partially
supported by Consejo de Investigaciones Científicas (CIC-UES) under the 09.20
project.