Nanocomposites and nanomaterials

Optical absorption and luminescence of nanoscale tin dioxide films prepared using polymers
L. Filevska, A. Chebanenko, M. Klochkov, V. Grinevych, V. Smyntyna
Odessa I.I. Mechnikov National University, Odessa, Ukraine, 
lfilevska@gmail.com

One of the main sensory and electrode materials nanoscales tin dioxide shows a number of new features that can become a basis for expanding its practical applications. The appearance of photoluminescence at room temperature in the nanoscale forms of this material is one of such features.
We have obtained nanostructured films of tin dioxide by sol-gel method using polyvinyl acetate as a structuring additive. In this paper we present the results of studies of optical absorption, reflection, and photoluminescence of the films obtained at room temperature, depending on the polymer content in the initial solution used for films’ production.
Estimated from the reflection spectra, the band gap of the films was 2.98 eV (for 0.1% PVA) and 3.07 eV (for 1% PVA). Therefore, the size of the nanocrystals of the film obtained from the solution with a higher polymer concentration is less due to the limitation of the crystallite size by the structuring polymer molecules in the film production.
The reflection spectrum of the investigated tin dioxide film has an oscillating character in the energy region hν> 3 eV. This may be due to interference, which manifests itself at a film thickness comparable with the wavelength, as it was in the case, for example, in thin films of zinc sulfide [6]. A minimum is observed on the reflection curve spectrum at a frequency ωmin = 4.25 ∙ 1015 s-1. The calculated concentration of free electrons was 1.2 × 1019 cm-3.
The spectral position of the maxima of the PL bands does not depend on the PVA concentration, however, the intensity of the λmax = 580 nm band increases with increasing PVA concentration. Taking into account the energy position of the maxima of the PL bands in the investigated SnO2 films (1.63-1.68) eV and 2.14 eV, and also the band gap (about 3.1 eV), the observed PL bands may be associated with the radiative transitions of electrons from the conduction band of SnO2 to the levels of VO (100 °) and VO (130 °), respectively.
The results obtained are interesting from the point of view of the possible application of nano-sized tin dioxide as sensors for registration of optical signal.