[en] The ESR spectrum of Fe⁴⁺ was looked for in amethyst quartz. Besides saturated Fe³⁺ lines, ESR lines of a new paramagnetic center whose spin-lattice relaxation time is relatively short were observed. They could be attributed to Fe⁴⁺

No abstract available

No abstract available

[en] Optically detected magnetic resonance has been used to study luminescence and phosphorescence for a ZnS:ZnSe alloy of low Se content. Two emission bands are identified, corresponding to D-Asub(S) and to D-Asub(Se) recombinations respectively. Here, D is a shallow donor and the A centres are zinc vacancies with a hole localized on a neighbouring S or Se atom respectively. This leads to an interpretation of certain emission bands reported for other compositions of this alloy system. (orig.)

No abstract available

No abstract available

[en] Total and partial ionic and electronic c-axis dc conductivities were measured for single-crystal Al²O³:8 ppm Mg as a function of oxygen pressure and temperature. The sample is unsaturated at T>1360 ₀C but is saturated in equilibrium with a spinel precipitate phase at lower temperatures. The results are analyzed to give ionic mobility, thermodynamic parameters of oxidation reduction of Al²O³, and the solubility of MgO as a function of temperature. Oxidized samples are grayish purple due to the presence of a broad absorption band with maximum at 480 nm. Discoloration can occur by reduction (at high temperature) or by precipitation (at T<1000 ₀C); both proceed from the surface, involving migration of oxygen out of or of Al into the crystal. An explanation for the rapid diffusion regulating precipitation below 1000 ₀C is proposed. Recoloration at low temperature proceeds without a front and possibly involves oxygen diffusing into the sample along dislocations or subgrain boundaries. Hole-release studies at low temperature indicate that the hole binding energy in the defect Mg_Alsup x/, E_a< or =0.68 eV. The combined results of the present work suggest that free holes move as large, rather than small, polarons and that E_a = 0.68 eV

[en] The effect of low T infrared irradiation on certain shallow acceptors and on the deep donors EL2 present in LEC GaAs have been studied by a combined optical absorption and ESR method. When the EL2⁺ compensating defects have been converted to the neutral metastable state EL2^o*, holes are stabilised on the shallow acceptors. This shows that holes cannot recombine with EL2^o*, in other words the distortion producing the metastable configuration has pushed the EL2 level below the top of the valence band. (author) 8 refs., 2 figs

[en] Absorption spectra have been measured for a 10 nm CdTe(0.3% Mn) quantum well with electron concentration n_e up to 1.5x10¹¹ cm^-2. Following recent theory appropriate to low n_e, here ∼ 0.1/πa²_B, the spectra are interpreted in a 'strong exciton' model, where the oscillator strength of the excitonic resonance (X) is conserved, with screening and phase-space filling effects negligible. As n_e increases in zero-field and as the filling factor υ increases in magnetic field, the intensity of X is transferred to: (i) trion processes, namely exciton-one electron scattering and the trion resonance (T), and (ii) quatron processes, namely exciton-two electron scattering and trion-one electron scattering. in magnetic field, the three- and four-body scattering processes become discrete, combined 'exciton and cyclotron' and combined 'trion and cyclotron' excitations that take all the intensity of X and T for υ ≥ 1 and υ > 2, respectively. (author)

[en] Optical spectra associated with transitions that create or annihilate charged excitons X^- or X⁺ can be observed in quantum well heterostructures containing an electron gas or a hole gas, respectively. A review is given of properties of trion states in CdTe quantum wells in zero field and of the magnetic field-dependence of the circular polarization and oscillator strength of the trion optical resonance. The possibility that disorder is needed to stabilise trion stated in concentrated 3D electron or hole systems is discussed. (author)