Growth and spectral and luminescent properties of a new Cr<Superscript>4+</Superscript>:LiAlGeO<Subscript>4</Subscript> nonlinear crystal

Single crystals of a new promising laser material, Cr⁴⁺-doped germanium eucryptite Cr⁴⁺:LiAlGeO₄, are grown from the melt for the first time. The crystals grown exhibit nonlinear optical properties. Absorption and luminescence spectra of the crystals and their luminescence decay are studied at various temperatures. The luminescence lifetime at 1.2 μ m at 300 K is 10 μ s. Active centers in the crystal are identified, and crystal field parameters are estimated.     

73Ge NMR spectra in germanium single crystals with different isotopic composition

We have studied the influence of isotopic disorder on the local deformations in Ge single crystals from both experimental and calculation points of view. The nuclear magnetic resonance (NMR) spectra of⁷³Ge nuclei (the nuclear spin equals 9/2) in perfect single crystals of germanium with different isotopic content were measured at temperatures 80, 300 and 450 K. Abnormal broadening of the spectrum was found to occur when the magnetic field was aligned along the [111] axis of a crystal. The observed specific angular dependence of the quadrupole broadening was attributed to isotopic disorder among atoms of germanium sited around the⁷³Ge NMR probe. Local lattice deformations in germanium crystal lattice due to isotopic impurity atoms were calculated in the framework of the adiabatic bond charge model. The results obtained were applied to study random noncubic crystal field interactions with the nuclear quadrupole moments and corresponding effects in NMR spectra. Simulated second and fourth moments of resonance frequency distributions caused by the magnetic dipole-dipole and electric quadrupole interactions are used to analyze the lineshapes, theoretical predictions agree qualitatively with the experimental data.     

Effect of electron irradiation on the properties of germanium-doped gallium arsenide

The Hall effect, electrical conductivity (77–370 K), and photoluminescence spectra (77 K) are studied in single-crystals of nuclearly doped GaAs (NDG) and GaAs doped with Ge by the metallurgical method after irradiation by electrons (E= 1 MeV, D=1.1·10¹⁵–3.8·10¹⁸ cm^–2). Initial electron concentrations were n= 1.7·10¹⁷ cm^–3 and n₀=2.6·10¹⁷ cm^–3 respectively. In the GaAs doped during crystal growth by the Czochralski method the degree of compensation related to the amphoteric impurity Ge is higher (K=0.8) than in the NDG (K=0.4) for identical initial electron concentration. It was established that the rate of charge carrier removal in GaAs is lower than in NDG, while radiation defects are more thermostable in NDG. The energy spectrum of radiation defects and radiating recombination centers, and the basic steps in reestablishment of electrophysical and optical properties in GaAs and NDG are similar, i.e., they do not depend on the method of germanium doping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 82–86, April, 1991.     

X-ray photoelectron and auger spectroscopy analysis of Ge:Mn-based magnetic semiconductor layers

Thin (～60 nm) germanium layers supersaturated with a manganese impurity of 10–16 at % have been studied by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The layers have been fabricated by pulsed laser deposition onto a semi-insulating single-crystal GaAs substrate. The results of XPS analysis of the Ge:Mn layers reveal a change in the line shape of germanium and manganese (2p) in the surface region compared to deeper layers, which indicates a transition from the oxidized form of the base material (Ge²⁺ and Ge¹⁺) and impurity (Mn²⁺) near the surface to the unoxidized state of germanium (Ge ⁰) and manganese (Mn⁰) in the interior of the layer. The XPS spectra of the valence electrons of the Ge:Mn structure indicate that the density of states in the valence band of the ferromagnetic Ge:Mn structures is caused not only by mechanical mixing of germanium and manganese. The composition of heterogeneous inclusions in Ge:Mn films has been studied using scanning Auger microscopy.     

Growth and characterization of pure and doped L-Lysine monohydrochloride dihydrate (L-LMHCl) nonlinear optical single crystals

Semi-organic nonlinear optical single crystals of pure, Ni²⁺ and Cd²⁺ doped L-Lysine monohydrochloride dihydrate (L-LMHCl) were grown from aqueous solution by slow evaporation technique. Single crystal X-ray diffraction analysis reveal that the pure and doped L-LMHCl crystals belong to monoclinic system with the space group P2₁. The presence of functional groups present in the pure and doped crystals was determined qualitatively by using Fourier Transform Infrared (FTIR) spectroscopy. Optical absorption studies reveal very low absorption for the doped crystal than that of the pure crystal. Dielectric studies have been carried out for the grown crystals and the results were discussed in detail.     

Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.     

Luminescence peculiarities and optical properties of MgMoO<Subscript>4</Subscript> and MgMoO<Subscript>4</Subscript>:Yb crystals

Magnesium molybdate is considered as a promising material for cryogenic scintillation bolometers. The luminescence properties of MgMoO⁴ have been investigated on single crystals grown from melts of stoichiometric and nonstoichiometric compositions and on crystals doped with Yb³⁺ ions. Their optical properties are interpreted taking into account the anisotropy of the MgMoO⁴ crystal structure.     

Effect of K+ ion on the dielectric properties of metallo organic L-alanine cadmium chloride single crystals

The single crystals of pure and Potassium doped L-alanine cadmium chloride (LACC), a metallo organic nonlinear optical material is grown by a slow evaporation technique. The grown crystals were confirmed by single crystal, powder XRD analyses and atomic absorption studies. Dielectric measurements were carried out for different frequencies at different temperatures. The dielectric constant decreases due to the introduction of large ionic radius K⁺ ion in the pure LACC crystal. The low dielectric constant and dielectric loss suggest that it can be used as inter-metal dielectric material.     

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride

Good quality single crystals of pure and metal ion (Ni²⁺) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni²⁺doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni²⁺doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.     

Effect of Co2+ on the growth,optical properties and laser damage threshold of potential nonlinear optical l-alanine single crystal

Good transparent bulk single crystals of pure l-alanine (LA) and cobalt doped LA crystals have been synthesized and successfully grown by slow-cooling method from their aqueous solutions. The concentration of metal dopants in the mother solution with 0.5 mol% for cobalt was carried out individually and crystals were obtained with well defined morphology. The as grown metal doped and pure single crystals were characterized by single crystal XRD studies which confirm that the incorporation of metallic dopants has not changed the basic structure of the parent crystal. The absorption of these crystals was analyzed and the result confirms that they possess low absorption in the range 230–1100 nm. Fourier transform infrared (FTIR) spectroscopy was carried out to investigate the molecular vibrations of these crystals and to confirm the incorporation of the dopants. The thermal properties have been studied by TGA/DTA curves. The EDAX measurement and surface morphology were studied for pure and metal doped LA crystals. The second harmonic generation (SHG) signals were observed using Nd: YAG laser with fundamental wavelength of 1064 nm in pure and metal doped crystals. The laser damage threshold was measured for pure and metal doped LA crystals and also tested by using a Q-switched Nd: YAG laser showed enhanced LDT value for metal (Co²⁺) doped LA crystal compared to pure LA crystal due to the metallic substitutions thus proving their useful candidature for nonlinear optical applications.     

IR absorption and Raman spectra of single crystals of stable germanium isotopes

The Raman and IR absorption spectra of single crystals of germanium isotopes ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge in the region of phonon absorption and interband electronic transitions are studied at room temperature. The dependence of the Raman peak position on the atomic mass has the form ν ~ M^–1/2. The shifts of the phonon absorption peaks of individual isotopes with respect to germanium of natural isotopic composition ^natGe are determined. With increasing average atomic mass of germanium, these peaks shift to longer wavelengths. In the region of interband electronic transitions, the intrinsic absorption edge of ⁷⁶Ge is observed to shift by 1 meV to higher energies with respect to Ge of natural isotopic composition. For isotopes with atomic masses close to that of natural germanium (⁷²Ge,⁷³Ge, ⁷⁴Ge), we found no significant difference in the band gap width at room temperature.     

Growth aspects,spectral, thermal and hardness studies of rare earth cerium(III)nitrate doped zinc(tris) thiourea sulphate single crystals

Single crystals of pure and cerium(III)nitrate doped zinc(tris) thiourea sulphate (ZTS) were grown from aqueous solution by slow evaporation method. The cell parameters of the grown crystals were determined by single crystal X-ray diffraction analysis. Powder X-ray diffraction patterns were recorded and indexed for the structural confirmation. The presence of functional group in the compound has been confirmed by FTIR analysis. UV–vis absorption spectrum has been recorded to determine the cut-off wavelength of the crystal. TGA/DTA studies show thermal stability of the grown crystals. SEM-EDX analysis revealed the incorporation of the impurity (Ce³⁺) into ZTS crystals. The microhardness study reveals that the hardness number (H_v) increases with load for all the grown crystals of this work. From the values of work hardening coefficients, it was concluded that pure and cerium nitrate doped ZTS crystals belong to the category of soft materials. The second harmonic generation of cerium(III)nitrate doped ZTS crystals was confirmed by Kurtz–Perry powder method using Nd:YAG laser.     

Beryllium-hydrogen and zinc-hydrogen shallow acceptor complexes in germanium

New shallow acceptor complexes with hydrogenically-spaced excited states have been discovered in intentionally-doped crystals of otherwise ultra-pure germanium. The doping consists of >10¹⁴ cm⁻³ of group II impurities, and the crystals were grown under hydrogen atmosphere. The identification proposed in this paper is that of a hydrogen-group II impurity complex, with piezospectroscopic behavior of a 〈111〉-oriented defect.     

Effects of doping and preliminary processing on the magnetically stimulated mobility of dislocations in InSb single crystals

The effect of the type of conductivity and the doping level of InSb single crystals on the mobility of fast 60° dislocations in a magnetic field is discovered. It is found that doping of a pure InSb crystal with tellurium (n-type impurity) to 10¹⁸ cm^?3 reduces the mobility of dislocations to the background level. At the same time, in p-type InSb crystals doped with Ge with the same carrier concentration (10¹⁸ cm^?3), the magnetoplastic effect is manifested clearly. It is shown that preliminary mechanical loading and, hence, internal stresses in the crystal affect not only the mean path length of dislocations in a magnetic field but also the magnitude of the threshold magnetic field below which the magnetoplastic effect is not observed. Possible reasons for these phenomena are discussed.     

Die Züchtung von KCl-Einkristallen mit bekanntem Tl-Gehalt und die Bestimmung des Verteilungskoeffizienten

A modifiedCzochralski method for the growth of single crystals is described. This technique permits controlled doping of the crystal with easily volatile additives. The impurity distribution within the crystal is calculated. Analysis of crystal and remaining melt permits determination of the distribution coefficient. — Pure single crystals of KCl quite homogeneously doped with Tl in a range of molar concentration from 4.10^?8?1.10^?4 were grown by this method. Their Tl content was determined radiochemically to within 3%. The distribution coefficient was found to bek=0.31±10% throughout the range of concentration under investigation. It is shown that the effect of evaporation may not be neglected.     

Electron transfer in the structure of a photorefractive doped Bi<Subscript>12</Subscript>TiO<Subscript>20</Subscript>: Ru crystal

The ac conductivity of Bi₁₂TiO₂₀: Ru crystals has been studied in the frequency range 10²–10⁶ Hz and at temperatures 293–773 K. The experimental data have been analyzed in the framework of the model of correlated barrier hops. In this material, the potential barriers are due to the existence of a block structure, crystal lattice defects, and also the presence of a ruthenium impurity. The microparameters characterizing the charge transfer in doped bismuth titanate single crystals have been determined.     

Supercontinuum generation at 1.55μm using highly nonlinear photonic crystal fiber for telecommunication and medical applications

In this paper, we present a theoretical calculation of a highly nonlinear germanium (Ge) doped photonic crystal fiber with all-normal group velocity dispersion to design a supercontinuum (SC) light source at 1.55 μm. By doping 3% higher refractive index Ge inside the host silica, the nonlinear coefficient is increased to a value as large as 60.5 W^?1 km^?1 at 1.55 μm. A 10 dB bandwidth of a 120 nm SC spectrum for a 2.5 ps input optical pulse and a 10 dB bandwidth of a 190 nm SC spectrum for a 1.0 ps input optical pulse have been found using the same fiber length of 200m and input optical power of 18 W. The coherent lengths of the generated SC light sources are found to be 8.8 μm for a 2.5 ps input optical pulse and 5.6 μm for a 1.0 ps input optical pulse. Therefore, the highest longitudinal resolution at 1.55 μm is found to be about 4.0 μm for biological tissues.     

Growth,thermal and optical properties of cis-2,6-diphenyl-3-isopropylpiperidin-4-one – A new class of organic NLO material

A new class of organic nonlinear optical crystalline material, cis-2,6-diphenyl-3-isopropylpiperidine-4-one (3IPO), was prepared. The single crystals of the title material with good optical quality have been grown from its benzene solution by slow evaporation solution growth technique at ambient temperature. Vickers micro hardness measurement studies showed that the crystal belongs to a softer material category. The grown crystals were characterized through the spectroscopic techniques such as PXRD, UV–visible, FTIR and ¹H NMR spectra. The powder XRD reveals the structure of the crystal to be monoclinic system. The UV–visible spectrum was recorded to find the suitability of the title crystal for optical applications. FTIR & ¹H NMR spectra were recorded to confirm the presence of various functional groups and the molecular structure, respectively. The thermal stability of the crystal was established by TGA/DTA analysis. The second harmonic generation (SHG) in the crystal was confirmed using the modified Kurtz–Perry powder test employing Nd:YAG laser as the source of IR radiation and the SHG efficiency was found to be closer that of standard KDP.     

Electrical conductivity and colour centres in Tl-doped KCl crystal

The electrical conductivity and optical absorption of potassium chloride crystals doped with different concentrations of thallium have been measured before and after X-irradiation. The optical absorption spectrum exhibits the characteristic Tl⁺ ion band at 247 nm. The extrinsic conductivity and the absorption coefficient at 247 nm increase with impurity addition upto a certain concentration. Further increase in impurities decreases them. Room temperature X-irradiation decreases the Tl⁺ ion band and produces the F band. F centre concentration is higher in lightly doped crystal compared to pure or heavily doped KCl. These results have been interpreted in terms of formation of interstitial potassium ions and positive ion vacancies in the Tl-doped KCl lattice due to large ionic radius of Tl⁺ ions. The impurity ions precipitate into TlCl phase when the doping is heavy.     

Ferromagnetism in epitaxial germanium and silicon layers supersaturated with managanese and iron impurities

The possibility of laser synthesis of diluted magnetic semiconductors based on germanium and silicon doped with manganese or iron up to 10–15 at % has been shown. According to data on the electronic levels of 3d atoms in semiconductors, Mn and Fe impurities are most preferable for realizing ferromagnetism in Ge and Si through the Ruderman-Kittel-Kasuya-Yosida mechanism. Epitaxial Ge and Si layers 50–110 nm in thickness were grown on gallium arsenide or sapphire single crystal substrates heated to 200–480°C. The content of a 3d impurity has been measured by x-ray spectroscopy. The ferromagnetism of layers and high magnetic and acceptor activities of Mn in Ge, as well as of Mn and Fe in Si, are manifested in the observation of the Kerr effect, anomalous Hall effect, high hole conductivity, and anisotropic ferromagnetic resonance at 77–500 K. According to the ferromagnetic resonance data, the Curie point of Ge:Mn and Si:Mn on a GaAs substrate and of Si:Fe on an Al₂O₃ substrate is no lower than 420, 500, and 77 K, respectively.