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EN
Direct observation of the suppression of the Auger effect on shallow donors by the magnetic field in the luminescence of manganese ions in semiconducting CdF_{2}:Mn crystals is presented. The magnetic field decreases the probability of the Auger effect, which is spin-dependent energy transfer from the manganese ions to the electrons occupying shallow donors. This results in the increase in the decay times of the luminescence.
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Content available remote Use of Bistable Centers in CdF_{2} for Holographic Recording
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EN
It is shown that metastable centers in various semiconductors can be used for efficient hologram recording. This type of holographic materials has a very high dynamic range and sensitivity. Their major drawback for possible applications is low metastability temperature. This problem can be overcome by using CdF_{2}:Ga crystals, which exhibit metastability below 240 K. This material is suitable for writing thick and multiple holograms both in static and dynamic regimes.
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Content available remote Photostriction of CdF_{2}:In Crystals
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EN
Lattice relaxation accompanying phototransformation of In bistable centers from the ground, deep state to the shallow state in CdF_{2} crystal has been measured with the use of scanning tunnelling microscope. It is shown that relatively small macroscopic changes of the crystal length in the order of 1.8×10^{-6} accompany the phototransformation of In ions. Lattice expansion upon the influence of population of shallow donor levels in CdF_{2} explains the observed small changes of lattice constant during the process.
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Content available remote Thermally Induced Nonlinear Refraction in Cd_{1-x}Mn_{x}Te
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EN
Self-focusing of laser beams is observed in Cd_{0.5}Mn_{0.5}Te at room temperature. The far-field patterns of laser beam after passing through the cadmium manganese telluride crystal are investigated. The values of focal length as well as the absorption coefficient were measured as a function of intensity of laser radiation. From these measurements the values of nonlinear refractive index for Cd_{0.5}Mn_{0.5}Te are determined. The results indicate that the self-focusing observed in Cd_{1-x}Mn_{x}Te is due to a thermally induced change in refractive index.
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This work is devoted to experimental study of the effect of manganese concentration on thermoluminescent properties of YAlO_{3}:Mn crystals grown by the Czochralski method. A new type of emitting centers beside of Mn^{4+} and Mn^{2+} ions was revealed at low concentration of manganese ions in the crystal. These centers are responsible for the high-temperature thermoluminescent peak at 570 K. A potential of this thermoluminescent peak for thermoluminescence dosimetry application is discussed.
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Content available remote Self-Focusing and Optical Bistability in Cd_{1-x}Mn_{x}Te
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EN
Thermally induced self-focusing of laser beam and optical bistability in CdMnTe at room temperature has been investigated. Photothermal focal length as a function of intensity of laser radiation has been measured in Cd_{1-x}Mn_{x}Te for 0.3 ≤ x ≤ 0.6. The time-dependence of the transmitted power for various laser intensities has been investigated and the switching from the transparent to dark state has been observed. For the first time the optical bistable characteristic has been measured in CdMnTe. The results indicate that CdMnTe is a suitable material for cavityless, large contrast, thermally induced absorptive bistable operation in visible region.
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Content available remote Optical Properties of Molecular Beam Epitaxy Grown ZnSe on GaAs
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EN
Photoluminescence studies of molecular beam epitaxy grown ZnSe-on-GaAs layers are presented. The high sensitivity of the PL technique allowed for identification unintentional dopants in pure ZnSe sample. Characteristic photoluminescence lines due to extended defects were observed. The experimental results obtained show a correlation between intentional doping level and extended defects concentration. We conclude also that even though molecular beam epitaxy layers are grown at low temperature, the self-compensation mechanism may still be important. For heavily doped sample edge emission is deactivated likely due to efficient energy transfer link with deep donor-acceptor pair bands.
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Content available remote Holographic Recording with the Use of Bistable Centers in CdF_{2}
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EN
We show that bistability and metastability of In and Ga impurities in CdF_{2} crystals can be efficiently used in writing volume holographic gratings. Phototransformation of these impurities from the localized to the hydrogenic state leads to a large change of the local polarizability of the host, and thus a significant change of the refractive index. While CdF2:In can be used only at low temperatures (below 150 K), CdF2:Ga crystals are suitable for room temperature recording.
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Content available remote Four- and Two-Wave Mixing in Solids
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EN
The paper gives an overview of theory and presents several examples of application of some holographic techniques: four-wave mixing, self-scattering and beam coupling to study nonlinear optical properties of solids. Among them excitation energy transfer in chromium-doped vibronic laser materials and picosecond study of undoped CdTe are reported.
EN
An effect of lutetium co-doping on photoluminescent and thermoluminescent properties of the Mn²⁺-doped (Lu-Y)AP crystals (with Lu content from 0 to 20% with respect to Y) grown by the Czochralski technique has been studied. It was found that the maximum of the thermoluminescent peak at 200°C is shifted towards higher temperatures at Lu content more than 5%. At the same time the position of the second thermoluminescent peak near 350°C remains unchanged. The observed changes in the thermoluminescent peak position are discussed in terms of the point defects of the material.
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Content available remote Light-Induced Gratings in CdMnTeSe:In Crystals
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We show that DX-like centers in Cd_{1-x}Mn_{x}Te_{1-y}Se_{x}:In crystal can be used in writing volume holographic gratings. The scattering efficiency is higher than 10% which proves the dispersive character of the light-induced gratings. Two different metastable centers with different lattice relaxation were found in the crystal. Measurements of the power dependence of the degenerate four-wave mixing scattering efficiency testify that both of these centers have negative U properties.
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The synthetic ZnAl_2O_4 spinels doped with Cr^{3+} ions are prepared from ZnSO_4, Al_2(SO_4)_3, and Cr_2(SO_4)_3. The spinel single phase is detected from X-ray diffraction. Luminescence properties of Cr^{3+} in ZnAl_2O_4 were studied by low temperature luminescence and decay measurements. Four luminescence lines at 14570, 14520, 14460, and 14330 cm^{-1} were found to originate from structure distortion and the line at 14175 cm^{-1} - from chromium pairs. The broad emission band at about 13540 cm^{-1} is considered to arise from a new Cr^{3+} center in ZnCr_2O_4.
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EN
Photoluminescence and thermoluminescence of the oxygen-deficient Y₃Al₅O₁₂ (YAG), YAlO₃ (YAP) and Y₄Al₂O₉ (YAM) ceramics has been studied. Corresponding ceramic samples prepared by the same way however in oxidizing conditions (in air) were studied for comparison. The observed luminescent properties of the materials are related to the F-type centers created on the basis of oxygen vacancies, antisite (Y_{Al}) defects and uncontrolled Tb³⁺ impurity ions.
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Content available remote Transmission Second Harmonic Generation in Cd_{1-x}Mn_{x}Te at 1.064 µm
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EN
Second harmonic generation, created by nanosecond Nd : YAG laser pulses at 1.064 µm with relatively low intensity in Cd_{1-x}Mn_{x}Te bulk crystals and thin layers was measured in transmission geometry. The effect practically occurs in a very thin surface layer of the material and it is used as a rela­tively straightforward method of layer quality characterization. It is shown that the angular dependence of the second harmonic generation intensity in thin layers of CdTe with good crystallographic (and optical) quality agrees very well with the theory in contrary to the samples with some distortions from the ideal structure which exhibits large distortions from the theory.
EN
The results of picosecond photoluminescence kinetics of four different CdTe/CdMnTe multiquantum well structures grown by MBE on GaAs substrates are presented. The experimental results show that excitons in CdTe quantum wells are strongly localized by potential fluctuations. Photoluminescence decay times of the localized excitons are considerably shorter (about 120 ps) than those reported for free or quasi-free excitons. An influence of Mn in the barriers on exciton properties is demonstrated. For narrow quantum wells as well as for the multiquantum well structure with the highest Mn mole fraction the excitons migrate during their decay to the states with a lower potential energy. Longer decay times are observed for quasi-localized excitons. We show also that for strongly localized excitons the energy transfer between localized and donor bound excitons is less efficient.
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EN
The results of investigation of the influence of γ-radiation by ^{60}Co-source on the YAlO_{3}:Nd laser generation characteristics are presented in this paper. The significant decrease in the output energy after γ-irradiation was obtained. The energetic characteristics are restored after illumination of the γ-irradiated laser rods by 1000-10000 pulses of the pumping lamp light. The additional absorption spectrum is induced by γ-irradiation in the crystals. The nature of the created in this way colour centres is discussed. The mechanism of influence of the colour centres on generation properties of the crystals is discussed.
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Content available remote Investigation of Co Ions Diffusion in Gd₃Ga₅O₁₂ Single Crystals
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EN
Spatial changes of properties of Gd₃Ga₅O₁₂ (GGG) single crystals caused by diffusion of cobalt ions during high-temperature annealing (1200°C, 24 h) in Co₃O₄ powder are investigated. The registration of these changes was carried out by optical spectrophotometry, microscopy and micro-Raman scattering methods. Changes in structure of near-surface layers of the crystal were investigated by X-ray diffraction technique. It was shown that the additional absorption induced by annealing is related to intra-center optical transitions in Co²⁺ ions, which occupy tetrahedral positions in the garnet structure at the distances of 250-500 μm from the crystal surface. The dependence of induced absorption with depth has got a non-monotonous character with a maximum at 400 μm. A comparison of the results obtained by different methods allows to suppose that the thermal treatment of GGG in the presence of cobalt ions leads to formation of the structurally and chemically non-uniform layer with a width about 500 μm.
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Content available remote Optical Investigation of the Cu Ions Diffusion into Bulk Lithium Niobate
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Spatial changes of optical properties of bulk LiNbO₃ crystal were investigated after annealing in CuO powder. The incorporation of copper ions into the crystal was confirmed by registration of additional absorption spectra that revealed formation of the absorption bands of both Cu⁺ (400 nm) and Cu²⁺ (1000 nm) ions. The changes of optical absorption caused by thermal treatment were registered along the direction of diffusion by the probe beam perpendicular to this direction. The anisotropy of diffusion was revealed. The maxima were observed on the depth dependences of additional absorption both for the wavelengths of 400 and 1000 nm for all main crystallographic directions. The concentrations of copper ions were calculated in accordance with the Smakula-Dexter formula. The X-ray diffraction study revealed reflexes which probably belong to CuNb₂O₆, CuNbO₃ and CuO. The halo was observed on these diffraction patterns that confirms the formation of the scattering centers (about 1 nm in diameter) in the near-surface region.
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