Strilchuk G. Optical properties of semiconductor and metal particles imbedded in polymer matrix

Study of optical properties of thin nanocomposite films is a powerful tool for understanding physical properties and spatial structure of the material. Modelling of the optical properties of nanocomposite films is usually done within the frame of the effective medium theory. The dependence of absorption profiles on its concentration and shape was analyzed. It was established that as concentration as shape of inclusions strongly define absorption processes in the films. Thus, varying of particles shape from oblate to prolate ellipsoids leads to deformation and red shift of absorption profile. The model for calculation of optical properties of nanocomposite thin films with inhomogeneous distribution of inclusions along thickness of the film was proposed. The comparison of these experimental and theoretical absorption spectra allows us to make some conclusions about concentration, shape of the particles and shape distribution of the inclusions. The experimental spectra of the photoluminescence were measured during the process of sedimentation in the CdS nanocomposite powder. The modification of luminescence spectra detected during sedimentation time is associated with changing the dimension and shape distributions of CdS suspension. The optical properties of CdS particles with different shape are compared. The particles, characterized as spherical and rectangular, were made by sedimentation and catalytic method. Obtained particles were investigated with the help of transmission microscopy, PL technique and theoretical modelling. The calculated luminescence profiles were defined by the shape distribution of the particles in the suspension. Supposing that the three kind of the parallelepipedal (cube-like, plate-like and stick-like) and ellipsoidal (spherical, oblate and prolate ellipsoids) particles are presented in the suspension, we compare the calculated and experimentally obtained luminescence profiles. This comparison given us the relative parts of the particles concentration of different shapes. As a result we obtained that the suspension obtained with chemical synthesis method mainly consists of spherical. Such way proposes the approach which allows us to determine the parameters of nano-composite film which can not be measured directly. The films obtained by vacuum deposition method were characterized by different shape and dimensions of the inclusion particles. Absorption spectra of the films were measured in situ. Absorption properties of inclusions were analyzing taking into account focal field interaction. The absorption profiles calculated in the frame of the model were compared with absorption profiles measured experimentally. This comparing gives possibility to conclude about concentration, shapes and shape distribution of the inclusion particles. It was established that in the case of thin films with low concentration (21 % Au sample) of inclusions the shape of inclusions is mainly sphere. When the film becomes thicker and inclusions concentration increases, the shape of inclusions becomes mainlya prolate ellipsoid. Luminescence pectra of ZnS particles have been analysed in different dielectric matrixes and without matrix. Researches of composites with different concentration of semi-conductor inclusions were carried out. Increasing of luminescence for the nanocomposite sample ZnS / Teflon is about 1,5-2, in comparison with pure ZnS. It is possible to explain it as follows, energy, which can collects in the Teflon matrix, can pass into nanoparticles and participate in the luminescence process. Also, it is necessary to consider concentration clearing of the radiation. The form and the sizes of particles also influence a spectrum. Key words: optical spectroscopy, photoluminescence, effective susceptibility, nanocomposite films, semiconductor nanoparticles.