Absorption Of Single Crystals Research Articles

The high-dose and high-temperature monitors of reactor irradiation based on insulators

Radiation-induced changes of the structure and properties have been investigated for oxide and nitride materials, and the use of high-temperature insulators as temperature/dose monitors for in-reactor irradiation of materials test assemblies has been validated.It has been experimentally shown that the use of Al2O3 single crystals and BN ceramics provides means of monitoring the temperature of irradiation from 370 to 1900 K. The temperature is derived from measurements of the optical absorption or X-ray diffraction line shifts after post-radiation annealing of the monitors. We discuss the applicability of (a) the optical absorption and F-center luminescence spectroscopies of irradiated Al2O3 single crystals for gamma dose evaluation and (b) the isotopic analysis of irradiated BN ceramics for neutron dose evaluation.

Optical properties of aluminum nitride single crystals in the THz region

We report on measurements of the refractive indices and the absorption in bulk single crystals of aluminum nitride, in the region from 1 to 8 THz. The birefringence is approximately 0.2 and is larger than in the optical frequency range. Both indices exhibit normal dispersion with no pronounced absorption resonances. Optical power loss coefficients are approximately 2 cm−1 and 4 cm−1 and the estimated static dielectric constants are 7.84 and 9.22, for the ordinary and extraordinary polarization, respectively.

Effect of Al and Ce ion concentrations on the optical absorption and luminescence in Gd3(Al,Ga)5O12:Ce3+ epitaxial films

We have studied the effect of Al and Ce ions on the optical absorption and luminescence of singlecrystal (Pb,Gd)3–y Ce y Al x Ga5–x O12 (x = 2.02, 2.09, 2.13, 2.17, 2.22; y = 0.02, 0.06, 0.07) films grown on (111)-oriented single-crystal Gd3Ga5O12 substrates by liquid-phase epitaxy from supercooled high-temperature solutions using solvents of the PbO–B2O3 system and growth charges containing 2.0, 2.1, or 2.2 mol % aluminum oxide and 0.03 or 0.2 mol % cerium oxide. The shift of the absorption bands of the Ce3+ 5d 1 and 5d 2 levels has been determined as a function of Al concentration in the films. The intensity of the Ce3+ luminescence bands of the films has been shown to increase with increasing Al and Ce concentrations.

Synthesis, linear optical, non-linear optical, thermal and mechanical characterizations of dye-doped semi-organic NLO crystals

Organic laser dyes Coumarin 485, Coumarin 540 and Rhodamine 590 Chloride were used to dope potassium acid phthalate crystals (KAP). Dye-doped KAP crystals with different dye concentrations such as 0.01 mM, 0.03 mM, 0.05 mM, 0.07 mM and 0.09 mM (in the KAP growth solution) were grown. The linear optical, non-linear optical, mechanical and thermal characterizations of dye-doped KAP crystals were studied and compared to understand the effect of dye and dye concentration on the KAP crystal. Absorption and emission studies of KAP and dye-doped KAP single crystals indicated the inclusion of the dye into the KAP crystal lattice. The effect of dye and its concentration on the SHG efficiency of the KAP crystal was studied using the Kurtz and Perry powder technique. It was observed that the absorption maximum wavelength and concentration of the dye used for doping the KAP single crystal decided the SHG efficiency of the dye-doped KAP single crystals. The mechanical hardness of the dye-doped and undoped (pure) KAP single crystals were studied using the Vickner’s microhardness test. It was observed that doping the KAP crystals with the laser dyes changed them from softer material to harder material. Etching studies showed an improvement in the optical quality of the KAP crystal after doping with laser dyes.

Enhanced electric dipole transition in lanthanide complex with organometallic ruthenocene units.

Enhanced luminescence of a lanthanide complex with dynamic polarization of the excited state and molecular motion is introduced. The luminescent lanthanide complex is composed of one Eu(hfa)3 (hfa, hexafluoroacetylacetonate) and two phosphine oxide ligands with ruthenocenyl units Rc, [Eu(hfa)3(RcPO)2] (RcPO = diphenylphosphorylruthenocene). The ruthenocenyl units in the phosphine oxide ligands play an important role of switching for dynamic molecular polarization and motion in liquid media. The oxidation states of the ruthenocenyl unit (Rc(1+)/Rc(1+)) are controlled by potentiostatic polarization. Eu(III) complexes attached with bidentate phosphine oxide ligands containing ruthenocenyl units, [Eu(hfa)3(RcBPO)] (RcBPO = 1,1'-bis(diphenylphosphoryl)ruthenocene), and with bidentate phosphine oxide ligands, [Eu(hfa)3(BIPHEPO)] (BIPHEPO =1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide), were also prepared as references. The coordination structures and electrochemical properties were analyzed using single crystal X-ray analysis, cyclic voltammetry, and absorption spectroscopy measurements. The luminescence properties were estimated using an optoelectrochemical cell. Under potentiostatic polarization, a significant enhancement of luminescence was successfully observed for [Eu(hfa)3(RcPO)2], while no spectral change was observed for [Eu(hfa)3(RcBPO)]. In this study, the remarkable enhanced luminescence phenomena of Eu(III) complex based on the dynamic molecular motion under potentiostatic polarization have been performed.

The high temperature photoluminescence and optical absorption of undoped ZnO single crystals and thin films

The photoluminescence of undoped ZnO single crystals up to 1350 °C and the optical absorption of stress-relaxed, epitaxial ZnO thin films up to 1100 °C are reported. The photoluminescence intensity and power dependence with illumination flux are related to the crystal growth methods and stabilize after high temperature annealing. The observation of excitonic recombination at very high temperatures requires high illumination flux. It is found that the zero phonon line model reproduces the shift and the band gap narrowing as well as the free excitonic transition up to the cross-over with a defect level at 2.83 eV that occurs at 800 °C. A phenomenological model of the excitonic recombination band shape, taking account exciton-phonon losses and defect levels provides an excellent fit up to 2.2–2.4 eV (1100 °C). At these cross-over temperatures, an energy transfer is observed between the free exciton transition and defect transitions. However, at temperature above 1100 °C, the decrease of the band gap and the increase of thermal radiation, as well as the restrictions of our experimental set-up and particularly the illumination flux of the exciting laser, limit the analysis of the photoluminescence spectra measurements.

Optical and luminescence characterization of LiBaAlF6 single crystals

Far ultraviolet optical, luminescence excitation and pulse cathodoluminescence spectroscopy methods were used to determine the electronic structure properties of undoped single crystals of LiBaAlF6 (LBAF). The spectrum of the refraction index in the ultraviolet–visible range was recorded. The photoluminescence excitation spectroscopy was carried out for both the excitonic (4.3eV) and fast vacuum ultraviolet (6.6eV) emission bands of LBAF single crystals at 10K. Modeling of the photoluminescence excitation spectra for excitonic emission was performed to characterize the low-energy tail of the host absorption of LBAF single crystals. The pulse cathodoluminescence spectroscopy method was used to characterize the fast vacuum ultraviolet (6.6eV) emission band and proof its origination from the radiative core-valence transitions F− 2p→ Ba2+ 5p.

Absence of significant structural changes near the magnetic ordering temperature in small-ion rare earth perovskite RMnO3

Detailed structural measurements on multiple length scales were conducted on a new perovskite phase of ScMnO3, and on orthorhombic LuMnO3 as a benchmark. Complementary density functional theory (DFT) calculations were carried out, and predict that ScMnO3 possesses E-phase magnetic order at low temperature with displacements of the Mn sites (relative to the high temperature state) of ∼0.07 Å, compared to ∼0.04 Å predicted for LuMnO3. However, detailed local, intermediate and long-range structural measurements by x-ray pair distribution function analysis, single crystal x-ray diffraction and x-ray absorption spectroscopy, find no local or long-range distortions on crossing into the low temperature E-phase of the magnetically ordered state. The measurements place upper limits on any structural changes to be at most one order of magnitude lower than DFT predictions and suggest that this theoretical approach does not properly account for the spin–lattice coupling in these oxides and may possibly predict the incorrect magnetic order at low temperatures. The results suggest that the electronic contribution to the electrical polarization dominates and should be more accurately treated in theoretical models.

Crystal structure of the charge-transfer complex 2-(1,2,3,4-tetra-hydro-naph-thal-en-1-yl-idene)hydrazinecarbo-thio-amide-pyrazine-2,3,5,6-tetra-carbo-nitrile (2/1).

The reaction of 2-(1,2,3,4-tetra­hydro­napthalen-1-yl­idene)hydrazinecarbo­thio­amide (TTSC) with pyrazine-2,3,5,6-tetra­carbo­nitrile (tetra­cyano­pyrazine, TCNP) yields the title 2:1 charge-transfer adduct, 2C11H12N3S·C6N8. The complete TCNP mol­ecule is generated by a crystallographic inversion centre and the non-aromatic ring in the TTSC mol­ecule adopts an envelope conformation with a methyl­ene C atom as the flap. In the crystal, the thio­semicarbazone mol­ecules are connected through inversion-related pairs of N—H⋯S inter­actions, building a polymeric chain along the b-axis direction. The TCNP mol­ecules are embedded in the structure, forming TTSC–TCNP–TTSC stacks with the aromatic rings of TTSC and the mol­ecular plane of TCNP in a parallel arrangement [centroid–centroid distance = 3.5558 (14) Å]. Charge-transfer (CT) via π-stacking is indicated by a CT band around 550 cm−1 in the single-crystal absorption spectrum.

Tetrathiafulvalene-supported triple-decker phthalocyaninato dysprosium(III) complex: synthesis, properties and surface assembly.

Self-assembly of functional compounds into a prerequisite nanostructure with desirable dimension and morphology by controlling and optimizing intermolecular interaction attracts an extensive research interest for chemists and material scientist. In this work, a new triple-decker sandwich-type lanthanide complex with phthalocyanine and redox-active Schiff base ligand including tetrathiafulvalene (TTF) units has been synthesized, and characterized by single crystal X-ray diffraction analysis, absorption spectra, electrochemical and magnetic measurements. Interestingly, the non-centrosymmetric target complex displays a bias dependent selective adsorption on a solid surface, as observed by scanning tunneling microscopy (STM) at the single molecule level. Density function theory (DFT) calculations are utilized to reveal the formation mechanism of the molecular assemblies, and show that such electrical field dependent selective adsorption is regulated by the interaction between the external electric field and intrinsic molecular properties. Our results suggest that this type of multi-decker complex involving TTF units shows intriguing multifunctional properties from the viewpoint of structure, electric and magnetic behaviors, and fabrication through self-assembly.

ChemInform Abstract: Syntheses, Structures, and Optical Properties of the Indium/Germanium Selenides Cs4In8GeSe16, CsInSe2, and CsInGeSe4.

AbstractCompounds (V), (VI), and (VIII) are characterized by single crystal XRD and optical absorption spectroscopy.

Note: application of a pixel-array area detector to simultaneous single crystal X-ray diffraction and X-ray absorption spectroscopy measurements.

X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) are two main x-ray techniques in synchrotron radiation facilities. In this Note, we present an experimental setup capable of performing simultaneous XRD and XAS measurements by the application of a pixel-array area detector. For XRD, the momentum transfer in specular diffraction was measured by scanning the X-ray energy with fixed incoming and outgoing x-ray angles. By selecting a small fixed region of the detector to collect the XRD signal, the rest of the area was available for collecting the x-ray fluorescence for XAS measurements. The simultaneous measurement of XRD and X-ray absorption near edge structure for Pr0.67Sr0.33MnO3 film was demonstrated as a proof of principle for future time-resolved pump-probe measurements. A static sample makes it easy to maintain an accurate overlap of the X-ray spot and laser pump beam.

Targeting Cystalysin, a Virulence Factor of Treponema denticola‐Supported Periodontitis

Cystalysin from Treponema denticola is a pyridoxal 5'-phosphate dependent lyase that catalyzes the formation of pyruvate, ammonia, and sulfide from cysteine. It is a virulence factor in adult periodontitis because its reaction contributes to hemolysis, which sustains the pathogen. Therefore, it was proposed as a potential antimicrobial target. To identify specific inhibitors by structure-based in silico methods, we first validated the crystal structure of cystalysin as a reliable starting point for the design of ligands. By using single-crystal absorption microspectrophotometry, we found that the enzyme in the crystalline state, with respect to that in solution, exhibits: 1) the same absorption spectra for the catalytic intermediates, 2) a close pKa value for the residue controlling the keto enamine ionization, and 3) similar reactivity with glycine, L-serine, L-methionine, and the nonspecific irreversible inhibitor aminoethoxyvinylglycine. Next, we screened in silico a library of 9357 compounds with the Fingerprints for Ligands and Proteins (FLAP) software, by using the three-dimensional structure of cystalysin as a template. From the library, 17 compounds were selected and experimentally evaluated by enzyme assays and spectroscopic methods. Two compounds were found to competitively inhibit recombinant T. denticola cystalysin, with inhibition constant (Ki ) values of 25 and 37 μM. One of them exhibited a minimum inhibitory concentration (MIC) value of 64 μg mL(-1) on Moraxella catarrhalis ATCC 23246, which proves its ability to cross bacterial membranes.

Optical spectroscopy of the Nd3+ and Nd3+–Gd3+/Yb3+ centres in BaF2 single crystals and calculations on lanthanide-doped BaF2

Absorption and site-selective laser spectroscopy of BaF2 single crystals homogeneously doped with Nd3+ ions as well as heterogeneously doped with Nd3+ and either Gd3+ or Yb3+ ions, performed at 10K, is presented. In each case a single centre, assigned to be of C3v symmetry, is dominant. A heterogeneous Nd3+–RE3+ (RE being either Nd or Yb) is also present in each of the double doped crystals. Energy levels for six multiplets of the single Nd3+ centre and for three multiplets for each Nd3+–RE3+ centre are presented together with the 4F3/2 (R) multiplet fluorescence lifetime for each centre. Calculations give comparable solution energies for C3v and C4v symmetry Nd3+ centres in BaF2; the C3v symmetry configuration has lower energy for the preceding lanthanides while C4v is favoured from Sm3+ onwards.

Origin of anisotropy of the near band gap absorption in Tl4HgBr6 single crystals

The origin of optical absorption anisotropy in the Tl4HgBr6 single crystals was studied using the first principles density functional calculations with different exchange correlation potentials. The results of the performed benchmark calculations include the structural, electronic, and optical properties of Tl4HgBr6. To the best of the authors' knowledge, these results are reported for the first time. It was shown that Tl4HgBr6 has a direct band gap of about 1.8 eV. All obtained data were compared to the corresponding experimental data; peculiar features of the polarized experimental absorption spectra were explained. It was shown that varying properties of the Hg–Br chemical bonds along different directions in the crystal lattice are in charge of the optical anisotropy, which is clearly revealed in the experimental spectra. The first estimations of the direct band gap value, refractive index and optical birefringence are given in this paper.

Absorption of light by exchange coupled pairs of tetrahedrally coordinated divalent manganese in the helvite-genthelvite solid solution

Periodico di Mineralogia (2011), 80, 1 (Special Issue), 105-111 - DOI: 10.2451/2011PM0008 Special Issue in memory of Sergio Lucchesi Absorption of light by exchange coupled pairs of tetrahedrally coordinated divalent manganese in the helvite-genthelvite solid solution Ulf Halenius Department of Mineralogy, Swedish Museum of Natural History, Stockholm, Sweden ulf.halenius@nrm.se Abstract Intensified colours in the helvite-genthelvite solid solution series are demonstrated by means of single crystal optical absorption and electron microprobe techniques to be due to absorption of light by exchange coupled IV Mn 2+ - IV Mn 2+ pairs. The absorption bands caused by the pair transitions occur at energies, 21100, 22600, 23800, 26800 and 28400 cm -1 , that are comparable to those recorded for spin-forbidden single ion transitions in IV Mn 2+ , but the absorption coefficients of the bands are proportional to the square of the Mn-contents of the samples instead of simply showing a Lambert-Beer relationship to the Mn-content. The helvite structure, comprising four corner sharing MnO 3 S tetrahedra with a common sulphur anion apex, represents a favourable situation for formation of exchange coupled 3d-cation pairs. However, several common Mn-rich minerals, as, e.g., rhodonite, have comparably favourable structures that contain corner, edge or face sharing 3d-cation centred polyhedra. Consequently, may Mn 2+ -Mn 2+ pair absorption be a frequent cause for colour intensification in minerals. Key words : helvite; genthelvite; electronic spectroscopy; electron microprobe analyses.

Synthesis, structure and reactivity of group 4 corrole complexes

A series of early transition metal corrole complexes has been prepared via salt metathesis with the corresponding lithium corrole. Their characterization by single crystal X-ray diffraction, NMR, and absorption spectroscopy is described. Organometallic derivatives of the titanium complex were obtained via treatment of 2 with NaCp* or ClMgCH2SiMe3.

Calix[4]arene-Supported Mononuclear Lanthanide Single-Molecule Magnet

Three new single paramagnetic lanthanide-based complexes, [Ln(L)(LOEt)] (Ln(3+) = Dy(3+), Tb(3+), and Ho(3+)), are synthesized with the multidentate calix[4]arene ligand H2L (H2L = 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-dihydroxy-26,28-dimethoxycalix[4]arene) and Kläui's tripodal ligand LOEt(-) (LOEt(-) = (η(5)-cyclopentadienyl)tris(diethylphosphito-p)cobaltate(III)). All of the complexes have been characterized by single crystal X-ray diffraction analysis, thermal stability, absorption spectra, and magnetization measurements. The magnetic properties and magnetostructural correlation in this seven-coordinated system are investigated. The dysprosium complex 1 shows typical single-molecule magnetic behavior with characteristic magnetic hysteresis loops and the slow relaxation of magnetization.

On-line spectrophotometric method for monitoring weak residual absorption of CaMoO4 single crystals near the intrinsic luminescence peak

The optical and spectral characteristics of isotopically enriched Czochralski-grown 40Ca100MoO4 single crystals have been investigated. This material is promising for detecting double neutrinoless β decay. The possibility and the technique of spectrophotometric monitoring of weak residual absorption near the intrinsic luminescence peak of this scintillation material, which is designed for developing new-generation detectors of elementary particles, are considered.

3,6-Dithiophen-2-yl-diketopyrrolo[3,2-b]pyrrole (isoDPPT) as an Acceptor Building Block for Organic Opto-Electronics

The electron acceptor building block for π-conjugated copolymers, 3,6-dithiophen-2-yl-diketopyrrolo[3,2-b]pyrrole (isoDPPT), was synthesized following two routes. The comparison between isoDPPT and widely investigated 3,6-dithiophen-2-yl-diketopyrrolo[3,4-c]pyrrole (DPPT) in terms of molecular orbital computations, single crystal X-ray diffraction, optical absorption and cyclic voltammogram was utilized to elucidate structural and electronic structure differences between the two cores. Both units are found to be planar in the solid state, exhibit similar LUMO energy, however, isoDPPT exhibits a much deeper HOMO energy. Six isoDPPT-based polymers with optical bandgaps spanning from 1.44 to 1.76 eV were synthesized by copolymerizing isoDPPT with the following building blocks: 2,2′-bithiophene (for P1), 4,4′-bis(2-ethylhexyl)-dithieno[3,2-b:2′,3′-d]silole (for P2), 3,3‴-didodecylquaterthiophene (for P3), 4,8-didodecylbenzo[1,2-b:4,5-b′]dithiophene (for P4), 4,8-didodecyloxybenzo[1,2-b:4,5-b′]dithiophene (for P5) and 3,3′-bis(dodecyloxy)-2,2′-bithiophene (for P6). Field-effect transistors and bulk heterojunction solar cells based on isoDPPT copolymers were fabricated and the response compared vis-a-vis to those of some DPPT-based polymers. Hole mobility (μh) of 0.03 cm2/(V·s) and solar cell power conversion efficiency (PCE) of 5.1% were achieved for polymer P2.