The reflectivity of ZnO single crystals was measured a t near normal incidence in the energy region from 3 to 25 eV with linearly polarized light, the electric field vector lying perpendicular and parallel to the c-axis. From the reflectivity the optical constants n and k, the complex dielectric constant E = and the energy loss function L = IIm e-ll have been computed by a Kramers-Kronig analysis for both directions of polarization. The profiles of the spectra differ completely from those of other 11-VI compounds of the wurtzite structure. The energetic positions and the polarization dependence of the peaks in the reflectivity and the c2 spectra can be related to the results of the first complete band structure calculation accomplished by Rossler using the Korringa-Kobn-Rostocker method.Mit polarisiertem Licht (Photonenenergie 3 bis 25 eV) wurde bei nahezu senkrechtem Einfall die Reflektivitit von ZnO-Einkristallen senkrecht und parallel zur c-Achse gemessen und mittels einer Kramers-Kronig -Analyse die optischen Konstanten n und k, die komplexe Dielektrizititskonstante E = ~1 + i c2 und die Energieverlustfunktion L = IIm e-ll fiir beide Polarisationsrichtungen berechnet. Die Spektren weichen entscheidend von denen anderer 11-VI-Verbindungen mit Wurtzitstruktur ab. Die energetische Lage und die Polarisationsabhingigkeit der Maxima des Reflexions-und des E,-Spektrums stimmen jedoch gut mit den Ergebnissen der ersten Bandstrukturberechnungen uberein, welche kiirzlich von Rossler mit der Korringa-Kohn-Rostocker-Methode durchgefiihrt wurden.

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We report about E P R measurements on Fe-Cu complexes in ZnSe crystals, grown by iodine transport reaction. The crystals were doped with 500 ppm Cu and contaminated with l e s s than 30 ppm Fe (proof limit of the AM). The measurements were carried out with a commercial Varian-E-Line spectrometer .operating in the X-band (9.1 GHz) in the temperature range from 1 . 8 to 6 K. Table 1). The observation of the transitions within the first excited doublet (so-called central doublet) is here re-1 ) Str. d e s 17. Juni 135, 1000 Berlin 12, Berlin (West).