Ladislav Tichy

Photoinduced changes in the short wavelength optical absorption edge of a-As2S3 and a-As2Se3 thin amorphous films

Abstract Photoinduced changes in the optical gap ( E g ) and the slope ( B ) of the short wavelength optical absorption edge (SWOAE) were studied in a-As 2 S 3 and a-As 2 Se 3 thermally evaporated thin films at 78 K. It was found that E g and B values are intercorrelated, as indicated by the existence of a focal point of ( αℏω ) 1/2 vs. ℏω dependencies, where α is an absorption coefficient and ℏω is photon energy. The correlation between E g and B values is discussed within both the model of Davis and Mott, and Taucs model.

Photoinduced optical changes in amorphous Se and Ge–Se films

Films of amorphous Se, Ge15Se85, and Ge25Se75 were prepared by thermal evaporation. Measurements of photodarkening at 78 K showed that the optical gap (Eg) and the slope of optical absorption edge (B) are intercorrelated. The correlation between the photoinduced changes of Eg and B is discussed within both the model of Davis and Mott and Taucs model for optical transitions in amorphous solids.

Some Physical Properties of Li2O-TiO2-TeO2 and BaO-TiO2-TeO2 Glasses

Homogeneous yellowish and well transparent glasses (Li2O)x(TiO2)x(TeO2)1-2x and (BaO)x(TiO2)x(TeO2)1-2x , (x = 0.075, 0.1, 0.125) were prepared from corresponding oxides (purity 99+%). For prepared glasses the optical gap values were found in the region 3.2 eV – 3.4 eV and the temperature (T) coefficient of the optical gap (γ) varies in the narrow region 5.3×10-4 eV/K to 5.9×10-4 eV/K for 300 K < T < 580 K. Estimated values of non-linear refractive index (n2) were found in the region n2 [m2W-1] = 2.7×10-18 – 3.5×10-18 close to n2 values for similar glasses. Raman spectra measured indicate that connectivity of (BaO)x(TiO2)x(TeO2)1-2x network is more evolved than that one for (Li2O)x(TiO2)x(TeO2)1-2x glasses. TiO2 most probably assists to continuous network formation due to appearance of Te-O-Ti bridges.