Titania dioxide (TiO₂) layers were synthesized via the acid-catalysed sol-gel route using titania (IV) ethoxide, and then annealed at temperatures varying in the range of 150–700 °C. The research concerned the effect of annealing temperature on the structure of TiO₂ layers, their surface morphology, and their optical properties. Further, X-ray diffractometry, and Raman spectroscopy were used to determine the structure of TiO₂ layers. Scanning electron and atomic force microscopy were used to study the surface morphology of TiO₂ layers. Transmittance, reflectance, absorption edge, and optical homogeneity were investigated by UV-VIS spectrophotometry, while the refractive index and thicknesses of TiO₂ layers were measured using a monochromatic ellipsometer. Chromatic dispersion characteristics of the complex refractive index were determined using spectroscopic ellipsometry. Structural studies have shown that the TiO₂ layers annealed at temperatures up to 300 °C are amorphous, while those annealed at temperatures exceeding 300 °C are polycrystalline containing only anatase nanocrystals with sizes increasing from 6 to 20 nm with the increase of the annealing temperature. Investigations on the surface morphology of TiO₂ layers have shown that the surface roughness increases with the increase in annealing temperature. Spectrophotometric investigations have shown that TiO₂ layers are homogeneous and the width of the indirect optical band gap varies with annealing temperature from 3.53 eV to 3.73 eV.

Tris(8-hydroxyquinoline)aluminium with poly(N-vinylcarbazole) (Alq ₃:PVK) or polystyrene sulfonate (Alq ₃:PSS) were deposited by spin-coating on glass and silicon substrates. SEM measurements show that relatively smooth thin films were obtained. Fourier transform infrared measurements were performed to confirm the composition of the samples. The optical properties of thin films containing Alq ₃:PVK and Alq ₃:PSS were characterised using absorption spectroscopy and spectroscopic ellipsometry. It was found that the absorption spectrum of Alq ₃:PVK is characterised by four bands, while for Alq ₃:PSS only three bands are visible. The photoluminescence of the studied thin layers shows a peak with a maximum at about 500 nm. Additionally, cyclic voltammetry of Alq ₃ is also presented. Theoretical density functional theory calculations provide the insight into the interaction and nature of Alq ₃:PVK and Alq ₃:PSS excited states. Finally, the organic light-emitting diode (OLED) structure based on Alq ₃:PVK was fabricated and showed strong electro-luminescence with a green emission at 520 nm. The results of the device show that the ITO/PEDOT:PSS/Alq ₃:PVK/Ca/Al system can be useful for the production of low-cost OLEDs with Alq ₃:PVK as an active layer for future lighting applications.