Nanocomposites and nanomaterials

Origin of light emission features of ZnO/ polyvinylpyrrolidone nanocomposite.
Isaieva O.F.1,2, Rudko G.Yu.1,2, V.I. Fediv3, Dzhagan V.M.1, E.G. Gule1
1 V. Lashkaryov Institute of Semiconductor Physics of National Academy of Sciences of Ukraine, 45, Pr. Nauky, Kiev, 03028, Ukraine.

E-mail: o.isaieva@ukma.edu.ua
2 National University “Kyiv-Mohyla Academy”, Skovorody, 2, Kiev, 04070, Ukraine.
3 Department of Biophysics and Medical Informatics, Bukovinian State Medical University, 42 Kobylyanska st., 58000, Chernivtsi, Ukraine.

Nowadays composites, the materials composed of several different materials, gain more and more applications in various fields. The properties of these materials are not a simple sum of the components’ properties, but often they demonstrate new intriguing features. The emerging novel type of composites – organic-ingorganic nanocomposites – is one of the rapidly developing fields in material science. The class of organic-inorganic composites attracts considerable interest due to the possibility to combine rather opposite characteristics. 
The object of the present study is organic-inorganic nanocomposite which consists of polyvinylpyrrolidone (PVP) as a matrix and zinc oxide nanoparticles as a filler (ZnO/PVP). The material can be used in blue/UV optoelectronics, electronics, fluorescence labels in medicine and biology. We investigate the optical properties of nanocomposite ZnO/PVP, namely, the origin of spectral components of photoluminescence spectra by studying emission of composite as a whole and its constituents at various conditions (intensity and wavelength of exciting light, temperature). Luminescence spectra of ZnO/PVP nanocomposite consist of three rather wide bands with peak positions at ≈ 3.5, 3.1 and 2.48 eV. Analysis of the bands origin showed that they can be reliably ascribed to different components of the composite. High-energy band was ascribed to unreacted zinc acetate residuals. Peak at 3.1 eV is the emission related to polymer matrix. Low-energy peak corresponds to the defect-related emission of ZnO nanoparticles, namely, to oxygen vacancies. The contribution of low-energy radiation increases significantly with increasing intensity of exciting light while the band associated with the emission of PVP matrix dominates at low temperature.