Author(s):
1. Jovan Šetrajčić, Akademija nauka i umjetnosti Republike Srpske, Serbia
2. Sinisa Vucenovic, Republic of Srpska, Bosnia and Herzegovina
3. Ana Šetrajčić-Tomić, Univerzitet u Novom Sadu, Prirodno-matematički fakultet, Departman za fiziku, Serbia

Abstract:
In this paper, we presented a microscopic theory of the optical properties of nanoscopic thin crystalline molecular structures bounded by two surfaces. Exposure of such nanofilm to external electromagnetic fields results in the creation of excitons - but with different properties than those in the corresponding dimensionally unlimited (bulk) structure. Exciton states and energy spectra were calculated using the method of two-time and temperature-dependent Green's functions, and it was shown that two types of optical excitations could occur in films: bulk and surface exciton states. The exciton energy dispersion law shows a discrete behavior with non-zero values. Analysis of the dielectric properties of these crystalline nanosystems shows that the permittivity strongly depends on the thickness of the film, due to the quantum-size effect. In addition, the permittivity shows a very narrow and discrete dependence on the frequency of the external electromagnetic field, as a consequence of resonance effects. The influences of the boundary conditions on the absorption characteristics of these nanostructures were investigated in detail. Analyzes have shown that the broad absorption zone in the near-IR region of bulk crystals is reduced to only a few discrete absorption peaks in ultrathin films of the same crystallographic composition.

Key words:
Ultrathin film, Frenkel´s excitons, Green´s functions, permitivity, absorption index

Thematic field:
SYMPOSIUM A - Science of matter, condensed matter and physics of solid states

Date of abstract submission:
07.06.2023.

Conference:
Contemporary Materials 2023 - Savremeni materijali

Applied paper from author Final paper Paper for reviews