G. Born
University of Giessen
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Featured researches published by G. Born.
European Physical Journal A | 1970
G. Born; A. Hofstaetter; A. Scharmann
The influence of doping zinc oxide with lead has been studied by electron paramagnetic resonance technique. Beside the signal nearg=1.956 (electron trapped in an oxygen vacancy) the resonances of Pb3+-ions are observed. Due to the strong Fermi-contact-hyperfine interaction of the 6s-electron with the Pb-207-nucleus the Breit-Rabi-diagram is evaluated with the experimentally obtainedA-value. The dependences of the resonances on optical illumination and temperature are investigated.
Journal of Luminescence | 1970
G. Born; A. Hofstaetter; A. Scharmann; G. Schwarz
Abstract Luminescence and thermoluminescence of various tungstates have been observed. To investigate trapping phenomena comparing measurements on nominally pure and doped (10 -3 % Sm, 10 -3 % Pb, 10 -4 % Pb) single crystals of CaWO 4 were performed. Decay times, temperature dependence of luminescence yields, thermoluminescence with spectral composition of the emitted glowlight, thermally stimulated conductivity and photoconductivity were measured. EPR-work was done on all investigated systems; correlations between all methods were found. A paramagnetic hole center (related to the V k -center in the alkali halides) appears in all samples; its structure can be interpreted by discussing the EPR-spectra. This center is shown to be in the state of a “small polaron” and plays a dominant role in the energy storage and -transport in the tungstates. The results of the theory of polarons are verified by our experiments. The thermally activated hopping motion and the recombination mechanism are discussed. From all experiments for the whole class of tungstate and molybdate phosphors a unified luminescence model is suggested, that describes the transport properties correctly too. Interrelations with comparable mechanism in alkali halides are shown.
European Physical Journal | 1971
G. Born; A. Hofstaetter; A. Scharmann
The EPR-spectra of the2S1/2-state of Pb3+-ions in CaWO4 crystals show beside a large hyperfine interaction with the Pb-207 nucleus a pronounced superhyperfineinteraction of the (6s)-electron with four equivalent tungsten nuclei. From the Breit-Rabi-diagram the hyperfine splitting constantA can be determined; its reduction with regard to the free ion valueAf is discussed. The theoretical SHFS-EPR-spectrum is calculated under the assumption of localD4h- orD2d-symmetry at Pb3+-site which corresponds to ionic or covalent treatment of the bonding in tungstates. From the measured angular dependence of the superhyperfinestructure the principal valuesA∥ andA⊥ of the SHFS-tensor are obtained which indicate a molecular orbital of the unpaireds-electron with four tungstate groups via four nearest neighboured oxygen ions. With the analysed data the theoretical superhyperfine pattern is simulated.
European Physical Journal B | 1975
R. Biederbick; G. Born; A. Hofstaetter; A. Scharmann
The EPR spectrum of Mn2+ in CaMoO4, CdMoO4, CaWO4 and SrWO4 has been investigated in the temperature range from 4.2–380 K. Results are given for the Spin-Hamiltonian parametersb20 andb40. They are completed by data forb20 of Mn2+ in SrMoO4 [1] and discussed with respect to resonant vibrations.
European Physical Journal A | 1971
G. Born; A. Hofstaetter; A. Scharmann
The EPR-spectra of the2S1/2-state of Pb3+-ions in different host lattices are characterized by a pronounced hyperfine splitting constantA, a smallg-shift from the free spin valuege and an appreciable amount of superhyperfine interaction. The unpaired 6s-electron of the Pb3+-ion is predominantly found in molecular orbitals built from the central 6s-function and orbitals of the sorrounding ligand ions. This assumption leads to correct estimates of theg-shift (Watanabe theory) and the reduction ofA due to covalent bonding effects. Theg- andA-values are shown to be correlated.
Journal of Luminescence | 1973
G. Born; A. Hofstaetter; A. Scharmann
Abstract Selected examples of impurity ions with one unpaired electron in an unfilled shell are Pb 3+ ions in II–IV compounds (ZnO, ZnSe, ZnTe), Pb 3+ in CaWO 4 ,F centres in alkali halides and Ag 0 and Au 0 atoms in radiophotoluminescent (RPL) glasses. Comparative studies of EPR, luminescence, thermoluminescence and related phenomena were performed on systems with 2 S 1 2 state ions as central ions and systematically varying ligand ions in the temperature range from 1.6°K to 450°K. Luminescence bands attributed to internal transitions 2 P 3 2 , 1 2 → 2 S 1 2 ground state are reported especially with respect to the corresponding EPR data. All data are summarized in a molecular orbital model for the luminescence complex.
Physics Letters A | 1971
G. Born; A. Hofstaetter; A. Scharmann
Abstract EPR-spectra of Pb 3+ -ions in CaO and ZnO are studied at 1.6 K. The g -values and the reduction of the hyperfine interaction constants A are correlated with the partial electron transfer to the ligands.
European Physical Journal B | 1976
G. Born; A. Hofstaetter; A. Scharmann; B. Vitt
The hyperfine interaction of the (6s)1 electronic configuration of Pb3+ with Pb-207-nuclei (I=1/2) shows a temperature dependent Fermi-contact-term obeying aT4 × Debyeintegral law. This effect is correlated to increasing delocalisation with temperature.
European Physical Journal A | 1970
G. Born; A. Hofstaetter; A. Scharmann
The EPR-powder spectrum ofVk-centres in CaWO4 is simulated using the experimentally obtained principal values of theg-tensor. The influence of the finite linewidth ΔH on the resulting EPR-pattern is taken into account. With these results the existence ofVk-centres in x-rayed microcrystalline tungstate powder is proved. The resonance of the2S1/2-state of Pb3+-ions substitutionally incorporated on Ca2+-sites in CaWO4 is measured in the powder spectrum. The optically and thermally stimulated valence state changes of the centres are studied and are shown to be correlated with the thermoluminescence glow curve.
Physica Status Solidi B-basic Solid State Physics | 1975
R. Biederbick; G. Born; A. Hofstaetter; A. Scharmann