Präparation und Lumineszenzeigenschaften von Zinkoxid

ZnO-phosphor powders are produced in systematic preparation series by annealing in an atmosphere containing H₂ or O₂. The samples have different quantum efficiencies, thermoluminescence light sums, and glow curve forms. The following explanation for the luminescence mechanism of ZnO can be confirmed: 1. The green luminescence is caused by intrinsic lattice imperfections. 2. Oxygen defects are the activators for the green luminescence. 3. Oxygen ions on interstitial sites produce hole traps, the energetic depth of which is caused by different coupling with oxygen defects.     

Das K-Auger-Spektrum von Neon

TheKLL-Auger spectrum of neon was investigated with an electrostatic spectrometer with an energy resolution of 0.12%. The ionization in theK-shell was caused by electron impact. The use of a gaseous target made it possible to measure the Auger electrons without any energy loss. The relative intensities of the KLL-lines were determined to be:KL ₁ L ₁(¹ S ₀)=1.0;KL ₁ L _2,3(¹ P ₁)=3.06±0.07;KL ₁ L _2,3(³ P _0,1,2)=0.98±0.05;KL _2,3 L _2,3(¹ S ₀)=1.67±0.08;KL _2,3 L _2,3(¹ D ₂)=13.1±0.6;KL _2,3 L _2,3(² P _0,2)=0. This is in agreement with an earlier measurement byKörber andMehlhorn but disagrees with all theoretical values calculated nonrelativistically for low Z. It is shown that agreement may be achieved by applying quantitatively the configuration interaction, introduced very recently byAsaad, and using improved wave functions for the calculation of the transition amplitudes. As a consequence of the ionization by electron impact also theKL-LLL Auger spectrum was caused. 10 lines of this spectrum were measured and identified. Moreover, from the Auger energies measured, the binding energyE(K) of neon was calculated to be E(K)=(870.0±0.4) eV.     

Neue Kupferzentren in Zinkoxid

Electron spin resonance investigations of electron irradiated zinc oxide single crystals doped with copper have been performed. Beside the known Jahn-Teller spectrum of the Cu _ioct ⁰ centre the resonances of four new copper defects have been observed. The ESR parameters are explained assuming one unpaired electron in the otherwise filled 3d shell. The electron configurations are discussed under the conditions of the covalent ZnO bond.     

Das Strom-Spannungs-Widerstands-Ersatzschaltbild von Elektreten

For one-dimensional electrets there is set up a current-voltage-resistance equivalent circuit, the aim of which is to change the boundary value problem of electrostatics, that is the calculation of the electric fields in electrets from the electric and geometric data and the applied voltage into a problem of network analysis of a circuit consisting of ohmic resistances, current sources and voltage sources.      

Das Neutroneneinfangspektrum von Sm150

The internal conversion electrons and the gamma-rays emitted by Samarium after neutron capture were measured by means of a betaspectrometer and a bent-crystal spectrometer at the research reactor at Garching near Munich. Lines corresponding to 50 transitions between 59 keV and 1·7 MeV were found with the betaspectrometer. The measurement with the crystal spectrometer showed 11 lines between 250 keV and 740 keV. The multipolarity of a few lines was determined. A level scheme containing most of the measured lines is suggested.     

Eigenst?rstellen in elektronenbestrahltem Zinkoxid

The ESR of zinc oxide single crystals irradiated with 6 × 10¹⁸ electrons/cm² consists of five spectra resulting from interstitial oxygen ions and from holes trapped at zinc vacancies. Irradiation with visible light during the ESR measurements allows to determine the energy levels of the centres. Further the influence of the paramagnetic defects on the electric conductivity is discussed.     

Elektrotransmission und Pockelseffekt an Zinkoxid

We report measurements of the electrotransmission on zincoxide. The main interest is on a structure due to the Pockelseffect. The later causes a rotation of the ellipsoid of wave normals near the isotropic point (Δn=0 for λ_i=396.3 nm) and produces, combined with the dichroitic absorption, a pronounced modulation of the transmitted light intensity, which is not connected to a critical point in the band-structure. The observed structure can be explained and calculated in detail by means of the phenomenological theory of Pockels taking into account the symmetry of the total system crystal and electric field. Two values of the Pockels-constants at low frequencies are given.     

Das kritische magnetische Verhalten von EuO

Mössbauer effect and magnetization measurements were employed in order to study the static and especially the dynamic magnetic properties of the nearly Heisenberg ferromagnet EuO near its Curie temperature,T _c=69.2 °K. The critical exponent β of the spontaneous magnetization was determined to be β=0.34±0.02. It was shown that critical slowing down of spin fluctuations takes place nearT _c with spin relaxation times between 7×10^?11 sec (T=1.01T _c) and 1.5×10^?1 sec (T=1.03T _c). The experimental values of the relaxation time were found to be in satisfactory agreement with theoretically computed ones. Just belowT _c the Mössbauer spectra exhibit relaxation effects, which are characteristic for the occurence of critical super-paramagnetism. Investigations of several samples indicated quantitatively, that critical superparamagnetism has its origin in the non ideal composition of the real crystal.