Vladimír Labaš

Order and disorder and their influences on optical absorption of glasses in the gap region

The exponential increase of the absorption coefficient near the absorption edge is usually explained by existence of the density-of-states tails. Among the quoted theoretical models which are widely used to explain the manifestations of the Urbach rule in semiconductors, are the Sumi–Toyozava and the Dow–Redfield models and ab initio (from begining) theory. Our barrier-cluster-heating model assumes the different creating mechanism of exponential tails. The energy by optical transition is provided to electrons except from photons also from vibration of microregion. It deals about the replenishment of absented photons energy, which is smaller as gap width. Absented energy needed for the transition by light absorption is acumulated in certain microregions of material in the form of vibrational energy. At absorption sufficiently big package of accumulated energy can be used. Energy of emptied microarea is filled by phonons from surrounding of microarea (as result of temperature status of surrounding), resp. p...

Monitoring the Influence of Chemical Composition of Electrical and Dielectric Properties of Special Glasses

Monitoring the Influence of Chemical Composition of Electrical and Dielectric Properties of Special Glasses The paper deals with the results of experimentally determined influence of the chemical composition change of pure Ge-Se-Te glasses systems with the rare earths elements additions (Pr, Er and Ho in oxide or pure metal form) on electrical and dielectric properties of the glasses. We used chalcogenide bulk glasses Ge20Se80-xTex for x ∈ (0, 5, 10, 15) prepared by systematic replacement of Se by Te. We wanted to find how electrical and dielectric properties of chosen chalcogenide glasses change with the change of content and form of rare earths. We carried out the measurements at different temperatures from 20 °C to 170 °C. Results show that the inhomogeneity and defects in the measured glasses have had an impact on the measured dielectric parameters.