B. Frumarova

Optically and thermally induced changes of structure, linear and non-linear optical properties of chalcogenides thin films

Abstract The spectral dependence of third-order non-linear susceptibilities, χ (3) , of amorphous As–S thin films was evaluated from changes of index of refraction using Miller’s rule. The exposure of thin fresh evaporated films and their annealing increases χ (3) , it increases also their homogeneity and level of their polymerization as can be judged from Raman spectra of the films. The large covalently bonded parts (‘molecules’) of the samples are apparently favorable for increase of χ (3) .

Amorphous and Glassy Semiconducting Chalcogenides

Chalcogenide glasses and amorphous films are quite transparent in the infrared region of spectrum. They are very attractive materials for infrared optics, infrared fibers, and also for light amplifiers and lasers, photoresist for nanometer-size resolution, optical waveguides, and gratings. Due to their high refractive index and high optical nonlinearities of the refractive index, they are also promising as active elements of all-optical circuits and devices. Their high nonlinearity of electrical conductivity offers the possibility of applying them in fast electrical switches. The fast crystallization and amorphization connected with large changes of optical reflectivity and electrical conductivity have been applied in phase-change nonvolatile memories (compact disks (CDs), digital versatile disks (DVDs), and Blue ray disks), and presently started replacing flash-type memories. The emerging multi-level phase-change memories do increase the storage capacity and promise to change the philosophy of data storage. Basic data concerning materials, their physical and chemical properties, their changes and their application in different areas, together with state of the art in understanding and application, are provided in this chapter.

Synthesis and properties of GeS2–Ga2S3:NdCl3 and GeS2–Ga2S3:Nd2O3 glasses

Abstract High purity (GeS2)80−x(Ga2S3)20·xNdCl3 (x=1, 2, 3) and (GeS2)79(Ga2S3)20·Nd2O3 glasses were prepared and their thermal and optical properties measured. The GeS2–Ga2S3 glasses can dissolve relatively large amounts of NdCl3 and Nd2O3 (≤3 mol%) and still form stable glasses. They are optically transparent in the range from 19000 cm−1 to 800 cm−1. The glass transition temperature (Tg≅378°C) and the glass-forming criteria are only slightly changed by Nd doping (ΔT=147°C, Hr=0.78; H′=0.39, S=4.10 K, where ΔT=Tc−Tg, Hr is Hrubys criterion, Hr=(Tc−Tg)/(Tm−Tc), H′=(Tc−Tg)/Tg, and S=(Tc−Tx)(Tc−Tg)/Tg). The short-wavelength absorption edge lies near 2.7 eV, doping with Nd creates new absorption bands which can be assigned to electron transfer from the 4 I 9/2 level to 4 G 7/2, 4 G 9/2, 2 K 13/2, 2 G 5/2, 2 G 7/2, 2 H 11/2, 4 F 9/2, 4 F 7/2, 4 S 3/2, 2 H 9/2, 4 F 5/2, 4 F 3/2, 4 I 15/2, 4 I 13/2 and 4 I 11/2 levels. In doped glasses, several broad luminescence bands, near 910, 1080 and 1360 nm, were found, which can be assigned to the transitions from 4 F 3/2 to 4 I 9/2, to 4 I 11/2 and to 4 I 13/2 electron levels. The long-wavelength absorption edge was found near 1000 cm−1 and is due to multiphonon Ge–S and Ga–S vibrations.