-In this work, we have studied the optical properties of CdSe colloidal quantum dots (CQDs) that undergo a ligand exchange. The QDs were synthesized by the thermal decomposition method and characterized by using optical spectroscopy techniques and Density Functional Theory (DFT) calculations. Trioctylphosphine (TOP) and Oleic acid (OA) ligands were replaced by Formic acid. This ligand exchange seems to cause an increment of the Stokes shift on the nanostructures. As a result a surface underpassivation of the nanostructures appears. This could be related to the generation of non-radiative states that decreases the quantum yield in our samples and a redistribution of the band edge electronic states that explain to some extent our observed results.
-In this work, we have studied the optical properties of CdSe quantum dots (QDs) with different sizes. Using the SIESTA code and the Kramers-Kronig relations, we have computed the imaginary part of the dielectric constant and the density of states (DOS). The absorption spectra are compared to experimental results from samples fabricated using the thermal decomposition method and a good agreement was obtained. The experimental band edge absorption could be associated to a specific optical transition in our QDs. A well defined second absorption band has been observed in our theoretical results. The energy maximum of these bands follow the expected quantum size effect. However, we do not observed the increase of the energy difference between them, reported by other authors. The reducing of absorption band intensity when the quantum dot size increases, has been seen. Preliminary density of states calculations, also reported in this work, allowed the association of Cd-or Se-character to the energy states in our samples.
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