Electronic and Optical Properties of Ag₂Se Quantum Dots as Obtained via Quantum Calculations

Quantum dots are of interest as optically-active elements for use in optoelectronic devices. Herein, we report on a combined experimental and theoretical study of Ag₂Se quantum dots (QDs). Experimentally, we have observed a size-dependent phase transition from an orthorhombic crystal phase in the bulk to a metastable tetragonal phase for crystallites below 40-nm in size. The theoretical studies are performed on finite-sized nanocrystals using a linear response theory within the time-dependent local density approximation, as implemented in VASP package. The calculated parameters include the absorption spectra, optical band gaps, ionization and transition energies of the tetragonal phase. All the electronic and optical properties are computed for QDs with varying sizes, and the effect of size on the resulting properties is analyzed. Theoretical data are compared with the experimental results obtained on disordered arrays of Ag₂Se QDs.