Mixed Single Crystals Research Articles

Evidence of Yb3+ band broadening and continuous wave laser operation in bismuth modified KY1-x-yBixYby(WO4)2 mixed single crystals

To increase the Yb3+ optical bandwidths in highly anisotropic β:KY(WO4)2 (KYW) type laser single crystals, the simultaneous contributions of the Bi3+ 6 s2 lone electron pair and Y3+/Bi3+ ionic radii mismatch is proposed. The top seeded solution growth method with K2W2O7 as solvent was used to grow Yb doped single crystals of the KY(WO4)2/KBi(WO4)2 (KYBiW) solid solution. Crystals obtained across the used KY1xBixW solid solution range show always the low temperature β phase, with the monoclinic C2/c crystalline structure, but important differences between the Y/Bi composition of the starting solute and that of the crystal grown are found. The incorporation of Y and Yb into the crystal is preferential, resulting in a low Bi segregation coefficient, SBi= 13%, on the KYW side but near SBi= 90% in the KBiW side (Yb is still strongly incorporated filling the remaining 10%). The saturation temperature of the melt decreases as the Bi concentration in the precursor KY1-x-yBixYby(WO4)2/K2W2O7 mixture increases. Evidence of optical absorption and photoluminescence broadening of the Yb3+ bands with Bi3+ incorporation is derived from 6 K and 300 K measurements. Laser operation of KY1-x-yBixYby(WO4)2 crystals is shown to be comparable to that of KY1−yYby(WO4)2 ones. Up to ≈ 0.5 W of output power is obtained pumping in continuous wave regime with a Ti sapphire laser with slope efficiency η ≈ 65% and pump threshold< 200 mW, which is within the usual performance of KYW:Yb crystals, but the spectral distribution of the laser output in KYBiW:Yb crystals is larger than that for KYW:Yb. This spectral broadening may help in the reduction of ultrashort (fs) laser pulse duration generated by modelocking.

Original Na5(Lu1–x–yGdxYy)9F32: Pr3+/Ho3+ Hybrid Single Crystals for Efficient ∼2.9 μm Mid-Infrared Emission

A novel Ho3+/Pr3+/Y3+/Gd3+ multiply doped Na5Lu9F32 mixed single crystal was successfully grown via a modified Bridgman technique. The structure of the mixed crystal was characterized by means of X-ray diffraction and Raman spectra. The impacts of Y3+ and Gd3+ ions on the 2.9 μm emission of Na5Lu9F32 single crystals, which incorporated fixed Ho3+/Pr3+, were investigated systematically with the aid of the optical spectra and decay curves of fluorescence. The 2.9 μm emission intensity (Ho3+: 5I6 → 5I7) was further heightened upon gradually introducing both Y3+ and Gd3+ ions into Ho3+/Pr3+-incorporated single crystals pumped at 640 nm. The brokenness of ionic quenching clusters of [Ho3+–Ho3+] and the release of more luminescent ions are in charge of the augment of emission at 2.9 μm by introducing Gd3+ or Y3+ ions into the Ho3+/Pr3+ codoped single crystals. A value of ∼8.2 × 10–21 cm2 was estimated for the maximum emission cross section at 2.9 μm of the mixed crystal. The processing of energy transfer among Ho3+, Pr3+, Y3+, and Gd3+ ions was investigated, and the energy transfer efficiency for Ho3+: 5I7 → Pr3+: 3F2 was approximately 57.32%. The Na5Lu9F32-doped Ho3+/Pr3+/Y3+/Gd3+ mixed crystals may be a new laser gain medium for 2.9 μm generation because of their special spectral and physicochemical properties.

Investigation on the bulk crystal growth, crystalline perfection, refractive index and piezoelectric properties of borate single crystals for piezoelectric and electro-optic applications

Low solubility potassium pentaborate tetrahydrate (KB5), ammonium pentaborate tetrahydrate (AB5) and mixed (KAB5) single crystals have been grown by the Sankaranarayanan-Ramasamy (SR) method. The crystal structures and space groups have been confirmed by powder XRD analysis. The direction of the grown crystal was confirmed by the back reflection X-ray Laue pattern. The crystalline perfection (CP) of the crystals have been evaluated using HRXRD studies. The transmittance spectra of the grown crystals were recorded by UV–Vis-NIR transmission studies showing that all the crystals have 90% transmittance in the entire visible region and found that the crystals' cut off wavelengths were below 200 nm. The optical studies such as refractive index (RI) and birefringence interferometry (BI) were reported. The RI for five different wavelengths of KB5, AB5 and KAB5 crystals were analyzed using the prism coupling method (PCM). Electromechanical behavior of the grown crystals was observed using piezoelectric coefficient (d33) measurement. Vickers Microhardness (VMH) measurement carried out at 30 °C shows increased hardness as the load increases.

MPD growth of single crystals of Ce3+ doped Gd3−xLuxAl5−yGayO12 mixed garnets and their luminescent, scintillation and photoconversion properties

This work deals with the growth of Ce3+ doped Gd3−xLuxAl5−yGayO12 mixed single crystals garnets by the micro-pulling down method and their development as phosphor-convertors of white LED (pc-WLED) and scintillators. In this research, the influence of combined technique of the “band-gap engineering” and “positioning of Ce3+ 5d-levels” in Gd3−xLux Al5−yGayO12 single crystals at x = 0 – 1.5 and y = 2–2.5 ranges, is studied with the aim to improve the material properties such as color-rendering properties of pc-WLEDs, as well as scintillation. The luminescent, scintillation and photoconversion properties of Gd3−xLuxAl5−yGayO12:Ce crystals were investigated as a function of the Gd/Lu ratio. We reviled that Gd3−xLuxAl3−2.5Ga2−2.5O12:Ce crystals at × = 1–1.5 show the best photoconversion and scintillation properties.

An unusual donor-acceptor system MnIIPc-TCNQ/F4-TCNQ and the properties of the mixed single crystals of metal phthalocyanines with organic acceptor molecules.

The interaction of manganese(ii) phthalocyanine with 7,7,8,8-tetracyanoquinodimethane and its perfluoro derivative proceeds with the oxidation of Mn and the reduction of the acceptor molecules to give the first mixed single crystals of manganese(iii) phthalocyanine with TCNQ/F4-TCNQ radical anions. The crystals have unusual structures with C-Hπ interactions between the ions and their orthogonal arrangement, as well as remarkable redox properties. The charge transfer was proved by spectroscopic and magnetic studies.

LD pumped quasi-three-level 928 nm laser with Nd:Gd0.69Y0.3TaO4 mixed crystal

We report on a 928 nm laser based on quasi-three-level transition of 4F3/2 → 4I9/2 in a Nd:Gd0.69Y0.3TaO4 mixed single crystal. With LD pumping at 808 nm, an output energy of 29.8 mJ at 928 nm is achieved with an optical-to-optical efficiency of 16.5% and a slope efficiency of 21.2%. In comparison, using 879 nm LD pumping, the maximum output energy at 928 nm reaches 48.5 mJ with an optical-to-optical efficiency of 33.4% and a slope efficiency of 38.0%.

Optical properties of Er3+-Yb3+ codoped Cd.7Sr.3F2 mixed single crystals

Absorption, excitation, fluorescence and decay spectra are carried out at room temperature on Er3+ (1%), Yb3+ (4%): Cd.7Sr.3F2 mixed single crystals. These crystals, with a good optical quality, are grown by the standard Bridgman method. This work concerns mainly the spectroscopic properties of the Er3+ ions incorporated in a fluorite-type crystal. Using the room temperature absorption spectra, the standard Judd–Ofelt (JO) model is applied to absorption intensities of Er3+ to obtain the three phenomenological intensity parameters by the least square fit procedure. The values obtained are in accordance with those of other fluoride hosts with good root mean square fitting. Compared to oxide materials, fluoride materials have, in general, low values ​​of Ω2. The low value of Ω2 is correlated to the cubic nature of the site occupied by the rare earth in the host matrix. These JO intensity parameters are then applied to determine the radiative transition probabilities (AJJ′), radiative lifetimes (τrad) and branching ratios (βJJ′) of Er3+ transitions. The green emission generated by the Er3+ ions directly excited in UV level, consisting in three well-resolved major lines, is more intense than the one. We have measured the fluorescence lifetime, the cross-section emission, the gain and the radiative quantum efficiency for both green and red band emissions. The obtained results are in good agreement with those of other fluoride laser crystals. From, the obtained spectroscopic data we suggest that Cd.7Sr.3F2 may offer green and red visible laser emission when doped with Er3+ ions.

Synthesis, Growth and Characterization Studies on Leucine and β-Alanine Mixed (La) single Crystal by Slow Evaporation Method

Synthesis, Growth and Characterization Studies on Leucine and β-Alanine Mixed (La) single Crystal by Slow Evaporation Method

Non-destructive analysis of didymium and praseodymium molybdate crystals using energy dispersive X-ray fluorescence technique

Abstract Analysis of didymium (Di) and praseodymium molybdate crystals were carried out using energy dispersive X-ray fluorescence (EDXRF). The assigned empirical chemical formulae of the composites were tested and verified by the EDXRF technique by estimating experimental major elemental concentration ratios. On the Basis of these ratios, the established formulae for some of the composite materials have been verified and suggestions made for their refinement. Non-destructive technique used in this analysis enables to retain the original crystal samples and makes rapid simultaneous scan of major elements such as La, Pr, Ned and Mo as well as impurities such as Ce. Absence of samarium(Sm) in the spectrum during analysis of didymium molybdate crystals indicated an incomplete growth of mixed rare earth single crystal. These crystals (e.g.,Di) are shown to be of modified stoichiometry with Ce as trace impurity.

Growth, thermal properties, and LD-pumped 1066 nm laser performance of Nd^3+ doped Gd/YTaO_4 mixed single crystal

A new laser crystal Nd:Gd0.69Y0.3TaO4 (Nd:GYTO) with high quality was grown by Czochralski method. The physical properties, including temperature dependent density, specific heat, thermal expansion coefficient, and thermal conductivity, were systematically characterized. The maximum absorption cross section at 809 nm and the stimulated emission cross section at 1066.6 nm are 6.886 × 10−20 cm2 and 22 × 10−20 cm2, respectively. The fluorescence lifetime is measured to be 182.4 μs. Up to 2.37 W of continuous wave (CW) laser operating at 1066.5 nm has been successfully realized, corresponding to an optical conversion efficiency of 36.5% and a slope efficiency of 38%. Compared with Nd:GdTaO4, Nd:GYTO shows an enhancement of the laser performance. These results demonstrate that Nd:Gd0.69Y0.3TaO4 is a novel laser crystal with low symmetry and has great potential as low to moderate power lasers.

Growth and characterization of K2ZnxNi1−x(SO4)2·6H2O mixed crystals for UV filters

The mixed single crystals of UV filter, potassium zinc nickel sulphate hexahydrate (PZNSHH) were crystallized by the slow evaporation technique. Unit cell parameters were determined by the single crystal X-ray technique. This X-ray technique reveals that the grown crystals belongs to the monoclinic crystal system with the space group P21/c. The functional group analysis was carried out using FT-IR spectroscopy in the range of 4000–400cm−1. The concentration of the doping was analyzed by the atomic absorption spectroscopic studies. The transmission property of the PZNSHH was investigated by UV–vis spectra. The thermal stability of the grown crystals were confirmed by TGA/DTA. This results shows that the presence of water molecule. The lower concentration of Zn metal shows the higher thermal stability and better efficiency for UV filter.

Phonon-lifetimes in demixing systems

The dynamics of silver–alkali halide mixed single crystals (AgxNa1−xBr, x = 0.23, 0.35, 0.40 and 0.70) were studied by inelastic neutron scattering during the process of spinodal decomposition. Using the thermal three-axes spectrometer PUMA as well as the time-of-flight spectrometer IN5, the time evolution of phonons was observed in time-resolved, stroboscopic measurements. Complementary to the study of long wavelength acoustic phonons, as studied previously, we extended these investigations to Brillouin-zone boundary modes that are particularly sensitive to variations of the local structure. Starting from the homogeneous mixed phase the behaviour of these modes during demixing is observed in real-time. A simple dynamical model based on local structure variants helps to interpret the results. It is shown that the phonon lifetimes vary strongly during the phase separation and increase drastically during the coarsening process. Up to a critical size of precipitates of about 10 nm, zone-boundary modes are found to be strongly damped, while beyond the line widths are reduced to the experimental resolution. This finding leads to the conclusion that the typical mean free path of these modes is of the order of 10 nm, which corresponds to 20 unit cells.

Crystal growth of mixed AlN–SiC bulk crystals

Bulk AlN–SiC mixed single crystals are prepared by sublimation growth employing pure AlN or mixed AlN–SiC sources and 6H-SiC seed crystals. As the growth temperature is increased from 1900 to 2050 °C, using seeds with different off-axis orientations, inclined up to 42° from the basal plane toward the (0 1 –1 0)-plane, or using different source materials, crystals with different Si/C contents are obtained. Dependent on the Si and/or C content, crystal coloration changes from yellowish to greenish to blackish. Modification in crystals’ coloration and corresponding changes in below band-gap optical absorption and cathodoluminescence spectra are discussed.

Effect of composition disorder on the electron paramagnetic resonance spectrum of the thermally populated excited state of Er3+ ions in YLuAG mixed garnets

The results of investigation of electron paramagnetic resonance of Er3+ ions in the thermally populated first excited state in (Y1 − xLux)3Al5O12 (YLuAG) mixed yttrium-lutetium garnet single crystals (0 ≤ x ≤ 1) are considered. In composition-disordered YLuAG, a number of new (as compared to Y3Al5O12 (YAG)) Er3+ paramagnetic centers are detected; these centers appear due to a change in the crystal field symmetry and magnitude upon isomorphic substitution of Lu3+ for Y3+ in the yttrium sublattice of garnets. The origin of new paramagnetic centers is established and their formation probability is calculated.

SYNTHESIS, GROWTH AND CHARACTERIZATION OF GLYCINE THIOUREA: A NOVEL NONLINEAR OPTICAL MATERIAL

A novel mixed organic single crystal of glycine thiourea (GTU), which is a potential material for nonlinear optical applications, has been grown by solvent evaporation method at room temperature. The grown single crystal has been analyzed using different characterization methods. X-ray diffraction studies show that it belongs to an orthorhombic crystal system having lattice dimensions a = 5.546 Å, b = 7.774 Å and c = 8.637 Å. The formation of the compound was verified by FTIR analysis. Its optical behavior was analyzed using UV-vis analysis and it was found that it had good optical transmission in the entire visible region. The mechanical properties of grown crystals were studied using Vickers microhardness tester. The surface defects were examined by adopting an etching technique. Its nonlinear optical property was tested using Kurtz powder method and found to have better SHG efficiency than that of potassium dihydrogen phosphate (KDP) single crystal.

Growth and Thermal, Electrical, Structural Characterization of Mixed Hydrated Single Crystal

AbstractMixed single crystal was made by mixing saturated aqueous solutions of NiSO4 · 6H2O and CuSO4 · 5H2O by volume (80:20) and the mixture was kept to form the crystals at room temperature by slow evaporation process. After some days, big pieces of greenish blue, dark colored crystals were grown. To determine the weight of NiSO4 · 6H2O and CuSO4 · 5H2O in the crystal, Ni‐DMG complexiometrical and EDTA gravimetrical analysis was done respectively. From this analysis it was concluded that 5.8 molecules of water of crystallization is present in the mixed single crystal. The crystals were characterized by UV‐Visible, FTIR and single crystal X‐ray diffraction studies. From single crystal XRD lattice parameters have been calculated. All these structural analysis confirms formation of new single crystal. Further, DTA‐TGA, dc electrical conductivity and dielectric constant studies were done from the room temperature to 400 °C.From DTA studies it was observed that 5.8 molecules of water of crystallization get dehydrated in four major steps at temperature 115 °C, 150 °C, 240 °C and 325 °C respectively corresponding to the detachment of 1 mole, 3 moles, 1 mole and 0.8 mole of water of crystallization. DC electrical conductivity and dielectric constant studies also show close agreement to the dehydration steps. The observed peaks in the conductivity verses temperature graph have been explained on the basis of release of water molecules and subsequent dissociation of these released water molecules into H+ and OH− ions.

X-ray fluorescence holography of [formula omitted] mixed crystal

The powder X-ray diffraction (PXRD) and X-ray absorption fine structure (XAFS) measurements were performed on In 1 - x Ga x Sb mixed polycrystals in the whole x range, and the former indicates Vegard's law, i.e., the lattice constant linearly changes with varying the concentration x , while the latter reveals a Pauling's bond length, i.e., an almost constant In–Sb or Ga–Sb interatomic distance is preserved all over the concentration range. In order to clarify the lattice distortions by adding the Ga atoms, Ga K α X-ray fluorescence holography (XFH) experiment was carried out on In 0.995 Ga 0.005 Sb mixed single crystal, and a three-dimensional atomic image around the Ga atoms was constructed. Although the atomic images locate almost on the atomic positions of the InSb crystal, some deviations (distortions from the lattice) can be observed, in particular for the first-, and second-nearest-neighboring atoms. We found that the lattice distortion by the Ga atoms is induced within the fifth neighbor atoms. From the XFH result, we discuss how the small GaSb 4 tetrahedra can be stably located in the InSb lattice with the larger lattice constant.

PEC behaviour of mixed single crystals of tungsten sulphoselenide grown by a CVT technique

Photoelectrochemical (PEC) solar cells have been fabricated with single crystals of WSxSe2−x (0⩽x⩽2) grown by chemical vapour transport (CVT) technique. Energy band location and redox analysis of the material have been done using Mott–Schottky plots. These studies justify the selection of appropriate electrolyte for the PEC work. Various solar cells with single crystals of WSe2, WS0.5Se1.5, WSSe, WS1.5Se0.5 and WS2 as photoelectrodes have been prepared. The solar cell parameters e.g. the fill factor (FF), open circuit voltage (Voc), short circuit current (Isc) and efficiency (η) for all the different cells have been determined. In order to see the effect of increasing the concentration of selenium on the photoresponse, the electrolyte and the intensity of illumination was kept constant and all the samples of WSxSe2−x were prepared from crystals showing absolutely plane faces. The results have been thoroughly described and the implications have been discussed.

Kinetics of decomposition in ionic solids: IV. Transition between nucleation and spinodaldecomposition observed by time-resolved phonon spectroscopy

Real-time inelastic neutron scattering has been used to study the kinetics of the demixingprocess in AgBr–NaBr mixed single crystals. The variation of transverse acoustic phononspectra provides most direct information about the microscopic non-equilibrium behaviour.The phase separation is monitored by a well defined splitting of phonon peaks thatreflects the different dynamical behaviours of the constituents. As a functionof temperature, time evolution of the phonon spectra changes drastically, thusproving unambiguously that the demixing process is dominated by nucleation in thehigh-temperature regime and by concentration fluctuations at low temperatures.

Structural Studies of (Ca,Sr)F2 Single Crystals with Raman and NMR Spectroscopies

Single crystal CaF2 is the material of choice for optics in the vacuum UV, due in part to its high transmission at these wavelengths. Unfortunately, as the wavelengths decrease, intrinsic birefringence (also referred to as spatial dispersion) can become larger than the target birefringence for precision optics at 157 nm, even for a cubic material such as CaF2. One elegant solution to this problem is to capitalize on opposite signs for this intrinsic birefringence, such as mixing SrF2 or BaF2 with CaF2. If the proper fluorides are mixed with the correct concentration, the intrinsic birefringence of the mixed single crystals can be minimized. It is also important that the resulting mixed single crystal maintain the high symmetry of CaF2, which requires that the cations mix randomly in the CaF2 structure. We show through Raman and NMR spectroscopic studies that this random mixing of cations can be achieved for mixed (Ca,Sr)F2 single crystals. A single Raman band is observed for all mixed crystals, which changes in both position and width upon addition of SrF2 to CaF2. 19F NMR spectra also reflect a random distribution of cations around the different fluorine environments in the mixed crystals.