Spektroskopische Untersuchungen an DyAsO4

DyAsO₄ undergoes a crystallographic phase transition atT _D=11.2K which is induced by a cooperative Jahn-Teller-effect. As deduced from the optical absorption spectra the distance between the two lowest lying Kramers doublets of the Dy³⁺ ion is increased from (6.1±0.5) cm^?1 aboveT _D to (25.0±0.5) cm^?1 at 4.2 K. BelowT _D the splitting factor of the lowest doublet becomes nearly uniaxial with a maximum value ofg _b =17.5±1.0 along the crystallographicb-axis. AtT _N=2.44 K the crystals order antiferromagnetically. The absorption lines of Er³⁺ ions in DyAsO₄ show already a splitting immediately belowT _D which is explained by magnetic short range ordering of the Dy³⁺ ions in the temperature rangeT _{N D} .     

Spektroskopische Untersuchungen über das thermodynamische Gleichgewicht der Anregung in den Plasmen kurzdauernder Impulsentladungen

The light emission of gases conducting electric discharges is of considerable complexity. The observed phenomenas are controlled to a great part by the electric parameters of the circuit, as well as by the time constants of the specific plasma properties as the relation times for reaching Maxwellian distribution and thermal equilibrium of electrons, ions, and atoms. The influence of the nonequilibrium between the excitation and the electron temperature on the population of states was studied in short time discharges by means of singulet and triplet lines of elements of the second group of the periodic system. In these discharges a nonequilibrium was found between the excitation and the electron temperature. While the time constant measured for the cooling of the electron gas was found to 7·10^?7 s in a discharge switched off 9·10^?7 s past the ignition the minimal time constant of relaxation of excitation is equal to the life time of the 2p ₂ state — this value of cadmium being 2.4·10^?6 s -.The use of Boltzmann and Saha equation must be considered very carefully in this type of short time discharges.     

Untersuchungen an zinndioxidschichten

Tin dioxide layers can be deposited at 250 °C and therefore on transparent substrates as glass and organic films. By deposition on silicon single crystals first an amorphous noncoherent layer is formed which transforms by longer deposition into a crystalline phase.     

Magnetooptik und elektronische Struktur der magnetisch ordnenden Europiumchalkogenide

The absorption coefficient and the interband Faraday rotation of EuS, EuSe and EuTe thin films have been measured as function of the photon energy (1–6 eV), the temperature (2.7–300 K) and the applied magnetic field (0–11.5 kOe). In addition a magnetic field modulation technique has been developed, with a resolution of 2 ? 10^?4 deg. This allows the measurement of the Faraday rotation in fields of only 100 Oe, which is important for metamagnetic samples with low critical fields. A Kramers-Kronig transformation of the Faraday rotation leads to the circular dichroism and from these two quantities and the optical constants the off-diagonal elements of the conductivity tensor have been computed. From a comparison of this experimental result with values obtained from a modified atomic model, we deduce the character of the involved transitions and the spin polarization of the occupied ground states (4f ⁷,p(anion)). In addition the ratio of exchange splitting to band width of the empty 5d final state can be evaluated. The fine structure of the first main peak is discussed in terms of Kasuya's coupling scheme between the 4f ⁶ multiplett and the excited 5d electron. In the antiferromagnetic EuTe the temperature dependence of the Faraday rotation does not follow the net magnetization of the sample for all photon energies, but some transitions show a “ferromagnetic” behavior. This is interpreted in Slater's model of the magnetic Brillouin zone.     

Die Bremsstrahlung von Plasmen bei geringer Ionisation

It is shown, that the continuous spectrum (free-free radiation) of a plasma in a thermal equilibrium — if the degree of ionization is slight — is produced not only by the electron-ion impacts, but also to a considerable extent by the impacts of electrons with the neutral atoms. Under this assumption the radiation of a mercury arc plasma in the infra-red is calculated. The results are in good agreement with absolute radiation measurements in a wide range of frequencies and pressures.