Doskaliuk N. Formation and optical properties of the composite layer by layer films based on CdTe/CdS nanocrystals

In the thesis the influence of the thermodynamic conditions of the layer by layer adsorption such as concentration of the polycation solution, ionic strength and pH of the nanocrystals solution on the components deposition efficiency and structure of layered composite films (poly(diallyldimethylammonium chloride) - CdTe/CdS nanocrystals)n, as well as the impact of external factors (temperature and irradiation) on the optical properties of CdTe/CdS nanocrystals embedded in polymer matrix have been investigated. It was shown that the optimum concentration of the polycation solution at which the macromolecules adsorb on the substrate surface in a flat uniform layer is in the range of 0,125 - 0,2%. The optimum pH of the solution of CdTe/CdS nanocrystals, at which both components of the film are in the ionized state, is in the range of 7,2 - 8,2. Increasing of the ionic strength of the nanocrystals solution facilitates their adsorption during layer by layer deposition. Depending on the efficiency of the excess loose macromolecules removing from the previous layer the film formation may occur in the mode of linear or exponential assembly. The temperature coefficient of photoluminescence energy maximum is in the range of 0,4 - 0,6 meV and decreases with increasing of the nanocrystals radii, due to the increasing of the quantum confinement of the carriers while the size of the nanocrystals reduces. Due to higher thermal expansion coefficient of water this parameter is higher in water than in the polymer matrix. Increasing the CdS shell thickness and reduction the Cd/Te ratio (bringing it closer to the stoichiometric) increases significantly the CdTe/CdS nanocrystals photostability. The modified method of synthesis of the type II CdTe/CdS nanocrystals was developed. The evaluation of the composite based on these nanocrystals as fluorescent light concentrator was conducted. The basic parameters of resonant nonradiative energy transfer process in CdTe / CdS - Ag system, including the Stern-Volmer constant and the F?rster radii was determined.