A Theoretical-Experimental Comparison of CdSe Quantum Dot Optical Properties

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 Cdor Se-character to the energy states in our samples.