Absorption Of Single Crystals Research Articles

Mixed Anion (Phosphate/Oxalate) Bonding to Iron(III) Materials

A novel phosphate/oxalate inorganic-organic hybrid material has been prepared to elucidate synthesis and bonding characteristics of iron(III) with both phosphate and organic matter (OM). Such mixed anion bonding of inorganic oxyanions and OM to iron(III) and aluminum(III) in environmental systems has been proposed but not proven, mainly because of the complexity of natural geochemical matrices. The compound reported here with the molecular formula of [C(3)H(12)N(2)](2)[Fe(5)(C(2)O(4))(2)(H(x)PO(4))(8)] (I) was hydrothermally synthesized and characterized by single crystal X-ray diffraction and X-ray absorption spectroscopy (XAS). In this new structure, Fe-O octahedra and P-O tetrahedra are connected by corner-sharing to form a 2-D network in the a-b plane. Oxalate anions cross-link these Fe-P layers constructing a 3-D anionic framework. A diprotonated structure-directing template, DAP (1,3-diaminopropane), resides in the oxalate layer of the structure and offsets the negative charge of the anionic framework. Iron K-edge XANES spectra confirmed that the iron in I is Fe(III). The crystal structure of I is used to successfully fit its Fe K-edge EXAFS spectrum, which exhibits spectral signatures that unambiguously identify iron-phosphate and iron-OM bonding. Such molecular spectroscopic features will be invaluable for the evaluation of complex environmental systems. Furthermore, syntheses demonstrated the critical role of the templating amine to mediate whether or not the iron(III) is reduced by the organic acid.

Single Crystal Structural and Absorption Spectral Characterizations of Nitric Oxide Synthase Complexed with Nω-Hydroxy-l-arginine and Diatomic Ligands,

The X-ray structures of neuronal nitric oxide synthase (nNOS) with N(omega)-hydroxy-l-arginine (l-NHA) and CO (or NO) bound have been determined at 1.91-2.2 A resolution. Microspectrophotometric techniques confirmed reduced redox state and the status of diatomic ligand complexes during X-ray diffraction data collection. The structure of nNOS-NHA-NO, a close mimic to the dioxygen complex, provides a picture of the potential interactions between the heme-bound diatomic ligand, substrate l-NHA, and the surrounding protein and solvent structure environment. The OH group of l-NHA in the X-ray structures deviates from the plane of the guanidinium moiety substantially, indicating that the OH-bearing, protonated guanidine N(omega) nitrogen of l-NHA has substantial sp(3) hybridization character. This nitrogen geometry, different from that of the guanidinium N(omega) nitrogen of l-arginine, allows a hydrogen bond to be donated to the proximal oxygen of the heme-bound dioxygen complex, thus preventing cleavage of the O-O bond. Instead, it favors the stabilization of the ferric-hydroperoxy intermediate, Fe(3+)-OOH(-), which serves as the active oxidant in the conversion of l-NHA to NO and citrulline in the second reaction of the NOS.

Wet etching and infrared absorption of AlN bulk single crystals

The defects and the lattice perfection of an AlN (0001) single crystal grown by the physical vapor transport (PVT) method were investigated by wet etching, X-ray diffraction (XRD), and infrared absorption, respectively. A regular hexagonal etch pit density (EPD) of about 4000 cm−2 is observed on the (0001) Al surface of an AlN single crystal. The EPD exhibits a line array along the slip direction of the wurtzite structure, indicating a quite large thermal stress born by the crystal in the growth process. The XRD full width at half maximum (FWHM) of the single crystal is 35 arcsec, suggesting a good lattice perfection. Pronounced infrared absorption peaks are observed at wave numbers of 1790, 1850, 2000, and 3000 cm−1, respectively. These absorptions might relate to impurities O, C, Si and their complexes in AlN single crystals.

Pr3+-doped complex oxide single crystal scintillators

We investigate and compare optical absorption, luminescence and scintillation properties of Pr-doped Y3Al5O12, Lu3Al5O12, Y2SiO5 and Lu2SiO5 single crystals. The processes determining the kinetics of the fast Pr3+ 5d–4f radiative transition are described. Among the studied host materials, only Lu3Al5O12 presents neither any 5d1–4f luminescence state nonradiative quenching nor Pr3+ ionization at room temperature. We evaluate the figure of merit of all materials for application as scintillators. The most promising system appears to be Lu3Al5O12 : Pr, since it combines an elevated density of 6.67 g cm−3, a fast scintillation response dominated by a 21 ns decay time and a spectrally corrected light yield about 160% with respect to that of Bi4Ge3O12 (BGO).

Investigation of nonlinear absorption in YAP and YAG single crystals doped with Co and co-doped with Si

AbstractSince our attempts to grow YAP:Co,Si non-linear absorbers have failed, we switched to Czochralski grown YAGs doped with the same ions. This time, however, the new material was found to exhibit excellent, non-linear absorption, which can be used directly in Q-switching elements in laser systems. In this work we report on technology of YAG single crystals doped with Co and Si, their optical properties, and, finally, on their non-linear absorption. An explanation on why the YAPs were found to be inefficient in non-linear absorption was also provided.

Syntheses, Structures, Physical Properties, and Electronic Properties of Some AMUQ3 Compounds (A = Alkali Metal, M = Cu or Ag, Q = S or Se)

The seven new isostructural quaternary uranium chalcogenides KCuUS 3, RbCuUS 3, RbAgUS 3, CsCuUS 3, CsAgUS 3, RbAgUSe 3, and CsAgUSe 3 were prepared from solid-state reactions. These isostructural materials crystallize in the layered KZrCuS 3 structure type in the orthorhombic space group Cmcm. The structure is composed of UQ 6 octahedra and MQ 4 tetrahedra that share edges to form (2) infinity[UMQ 3 (-)] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing AQ 8 bicapped trigonal prisms. There are no Q-Q bonds in the structure, so the formal oxidation states of A/U/M/Q may be assigned as 1+/4+/1+/2-, respectively. CsCuUS 3 shows semiconducting behavior with thermal activation energy E a = 0.14 eV and sigma 298 = 0.3 S/cm. From single-crystal absorption measurements in the near IR range, the optical band gaps of these compounds are smaller than 0.73 eV. The more diffuse 5f electrons play a much more dominant role in the optical properties of the AMUQ 3 compounds than do the 4f electrons in the AMLnQ 3 compounds (Ln = rare earth). Periodic DFT spin band-structure calculations on CsCuUS 3 and CsAgUS 3 establish two energetically similar antiferromagnetic spin structures and show magnetic interactions within and between the layers of the structure. Density-of-states analysis shows M-Q orbital overlap in the valence band and U-Q orbital overlap in the conduction band.

Magnetic, Optical, and Electronic Properties of the Phosphide Oxides REZnPO (RE = Y, La–Nd, Sm, Gd, Dy, Ho)

AbstractWell‐shaped yellow to red transparent single crystals of the phosphide oxides REZnPO (RE = Y, La–Nd, Sm, Gd, Dy, Ho) were synthesized from the elements and ZnO in NaCl/KCl fluxes in sealed silica ampoules. Four structures (NdZnPO type, R3m) were refined from single crystal X‐ray diffractometer data: a = 388.5(2), c = 3032(1) pm, wR2 = 0.0380, 360 F2 values for YZnPO, a = 394.6(2), c = 3071(1) pm, wR2 = 0.0587, 226 F2 values for SmZnPO, a = 392.2(2), c = 3056(1) pm, wR2 = 0.0262, 462 F2 values for GdZnPO, and a = 389.33(6), c = 3030.5(4) pm, wR2 = 0.0453, 217 F2 values for DyZnPO each with 14 variables per refinement. The structures are composed of alternate stacks of (RE3+O2−) and (Zn2+P3−) layers with covalent RE–O and ZñP bonding within and weak ionic bonding between the layers. The zinc and oxygen atoms have slightly distorted tetrahedral coordination by atoms of phosphorus and the rare earth element, respectively. According to the electron precise formulation RE3+Zn2+P3−O2−, these pnictide oxides are transparent in visible light. Susceptibility measurements on β‐CeZnPO, β‐PrZnPO, and GdZnPO reveal Curie‐Weiss paramagnetism with experimental magnetic moments of 2.31, 3.60, and 7.72 μB/RE atoms, respectively. β‐CeZnPO and β‐PrZnPO show antiferromagnetic order with Néel temperatures of 7.4 (Ce) and 2.2 (Pr) K. GdZnPO shows no magnetic ordering down to 2 K. Single crystal absorption spectra measured for REZnPO (RE = Y, La, Pr, Nd, Sm, Dy) in the NIR‐Vis region reveal unexpected variations for the optical band gap of these phosphide oxides. For RE = Pr, Nd, Sm, Dy, Ho f‐f electronic transitions with nicely resolved ligand‐field splittings are observed in the range 6000–20000 cm−1. DFT band structure calculations show similarity between the valence bands of tetragonal and rhombohedral REZnPO as they possess mainly P‐3p character. In both cases, the conduction bands have mainly Zn‐4s character, but a significant contribution of RE‐5d occurs in rhombohedral REZnPO, which is responsible for a smaller optical band gap for the latter compounds. Variations of the energy gaps of tetragonal REZnPO can be explained by hybridization of Zn‐4s + RE‐5d + RE‐4f orbitals for the conduction band. DFT volume optimizations of α‐ and β‐PrZnPO show β‐PrZnPO to be more stable by 10.7 kJ mol−1.

Effect of gamma irradiation on the optical spectra of undoped, Mg-doped, and Gd-doped LiNbO3 single crystals

We have measured the optical spectra of gamma-irradiated lithium niobate crystals of different compositions: nominally undoped and doped with rare-earth (Gd) and alkaline-earth (Mg) metals in the range 0.003–0.27 wt %. The difference in behavior between gamma-irradiated and vacuum-annealed nominally undoped lithium niobate single crystals has made it possible to elucidate the mechanisms underlying the formation of electronic and point defects in the crystals and to develop a model for the processes involved. The effects of gamma dose, doping level, and the nature of the dopant on the optical absorption of gamma-irradiated doped lithium niobate single crystals are analyzed.

An X-ray diffraction and X-ray absorption spectroscopy joint study of neuroglobin

Neuroglobin (Ngb) is a member of the globin family expressed in the vertebrate brain, involved in neuroprotection. A combined approach of X-ray diffraction (XRD) on single crystal and X-ray absorption spectroscopy (XAS) in solution, allows to determine the oxidation state and the structure of the Fe–heme both in the bis-histidine and the CO-bound (NgbCO) states. The overall data demonstrate that under X-ray the iron is photoreduced fairly rapidly, and that the previously reported X-ray structure of ferric Ngb [B. Vallone, K. Nienhaus, M. Brunori, G.U. Nienhaus, Proteins 56 (2004) 85–92] very likely refers to a photoreduced species indistinguishable from the dithionite reduced protein. Results from the XAS analysis of NgbCO in solution are in good agreement with XRD data on the crystal. However prolonged X-ray exposure at 15 K determines CO release. This preliminary result paves the way to experiments aimed at the characterization of pentacoordinate ferrous Ngb, the only species competent in binding external ligands such as O 2, CO or NO.

The interaction between the spin transition and a crystallographic phase transition in the spin-crossover compound [Fe(bbtr) 3](ClO 4) 2: Nucleation, formation of domains and fluctuations

The thermal and the light-induced spin transition in [Fe(bbtr) 3](ClO 4) 2 (bbtr = 1,4-di(1,2,3-triazol-1-yl)) as well as the high-spin → low-spin relaxation following the light-induced population of the high-spin state below the thermal transition temperature are discussed in relation to the accompanying crystallographic phase transition. The experimental data have exclusively been obtained using optical single crystal absorption spectroscopy.

Physical mechanism of two-photon response in semi-insulating GaAs

The physical mechanism of two-photon response (TPR) in semi-insulating GaAs is studied. The measured photocurrent generated from the fabricated hemispherical GaAs sample responding to 1.3 μm continuous wave laser shows a quadratic dependence on the coupled optical power and no saturation with the bias. The angular dependence of the photocurrent on the azimuth is in agreement with the anisotropy of double-frequency absorption (DFA) in GaAs single crystals. These results demonstrate DFA is the dominant mechanism of TPR in GaAs.

Hydrogen absorption and desorption kinetics in fullerite C60 single crystals. Low-temperature micromechanical and structural characteristics of the interstitial solid solution C60(H2)x

The microhardness HV and lattice parameter a of C60 single crystals are measured at room temperature as functions of the hydrogen saturation time t for several values of the saturation temperature (250, 300, and 350°C) at a fixed hydrogen pressure p=30atm. According to the measurements of HV and a, the kinetics of hydrogen absorption is described by a simple exponential law with a single, temperature-dependent characteristic time. In highly saturated samples the microhardness is 4 times greater than for the initial C60 crystal, while the lattice parameter is 0.2% larger. The temperature dependence of the microhardness HV and lattice parameter a of C60(H2)x crystals is investigated in the temperature interval 77–300K. The introduction of hydrogen lowers the temperature of the fcc–sc phase transition, and the transition becomes strongly broadened in temperature. The dependence of the microhardness of the saturated sample on the hold time in air at room temperature is described by the sum of two exponentials with different characteristic times. Kinetics of this kind is presumably due to two processes: desorption of hydrogen from the sample, which causes a decrease of the microhardness, and a simultaneous penetration of gaseous impurities into the sample from the surrounding air, which is accompanied by hardening. The influence of the H2 molecules on the characteristic of the intermolecular interaction in fullerite C60 is discussed and the intercalation-induced processes of dislocation slip and microfracture.

High performance organic field-effect transistors based on [2,2′]bi[naphtho[2,3-b]thiophenyl] with a simple structure

A novel semiconductor with naphtho[2,3-b]thiophene rings was synthesized and characterized by using single crystal X-ray structure analysis, absorption and emission spectra, electrochemical measurements, quantum chemical calculations, thin-film X-ray diffraction and AFM studies. FET devices using the molecule as the active layer showed high mobilities and high air stability. The hole mobility was enhanced to 0.67 cm2V−1 s−1 in air.

OH- Absorption of Zn-Doped LiNbO3 Single Crystals after Proton Exchange

An investigation of the OH- absorption spectra of Zn-doped LiNbO3 single crystals with doping concentrations from 0.0 to 8.3 mol % after proton exchange (PE) is carried out. Before PE treatment, the absorption bands are found centered at approximately 3485 cm-1 for the samples with Zn-doping concentrations below 7.5 mol %, whereas two distinct bands at 3505 and 3530 cm-1 are clearly observed for the samples with Zn-doping concentrations above 7.5 mol %. After PE treatment, an absorption band at 3505 cm-1 is predominant for all the samples, and this is attributed to the high concentration of H+ ions substituting Li atoms. However, for the highly Zn-doped samples, the lineshape and intensity of the 3530 cm-1 mode remain the same during PE. A theoretical investigation using the hybrid density functional B3LYP method with a simple cluster structure shows that the origins of the 3485 and 3530 cm-1 absorption modes correspond to the Li- and Nb-vacancy models, respectively.

Optical investigation of spin-crossover in cobalt(II) bis-terpy complexes

The spin transition of the [Co(terpy) 2] 2+ complex (terpy = 2,2′:6′,2″-terpyridine) is analysed based on experimental data from optical spectroscopy and magnetic susceptibility measurements. The single crystal absorption spectrum of [Co(terpy) 2](ClO 4) 2 shows an asymmetric absorption band at 14 400 cm −1 with an intensity typical for a spin-allowed d–d transition and a temperature behaviour typical for a thermal spin transition. The single crystal absorption spectra of suggest that in this compound, the complex is essentially in the high-spin state at all temperatures. However, the increase in intensity observed in the region of the low-spin MLCT transition with increasing temperature implies an unusual partial thermal population of the low-spin state of up to about 10% at room temperature. Finally, high-spin → low-spin relaxation curves following pulsed laser excitation for [Co(terpy) 2](ClO 4) 2 dispersed in KBr discs, and as a comparison for the closely related [Co(4-terpyridone) 2](ClO 4) 2 spin-crossover compound are given.

Structural and Spectroscopic Characterization of Active Sites in a Family of Light‐Emitting Sodium Lanthanide Tetrafluorides

Illuminating disorder: Many highly efficient light emitters are members of the family β-NaLnF4 (Ln=Y, La–Lu). Diffuse X-ray scattering is combined with single-crystal absorption spectroscopy at cryogenic temperatures to unambiguously identify and characterize two crystallographically inequivalent spectroscopic sites (A and B). The high light yield is correlated with the existence and nature of these sites.

01pA05 Float zone growth and broadening of the absorption and emission bands of Nd-doped vanadate single crystals(NCCG-36)

01pA05 Float zone growth and broadening of the absorption and emission bands of Nd-doped vanadate single crystals(NCCG-36)

Band gap in tungsten sulphoselenide single crystals determined by the optical absorption method

Optical absorption in single crystals of tungsten sulphoselenides has been measured at room temperature with the incident light beam normal to the basal plane, i.e. along c-axis of the grown crystal flakes. Results have been analysed on basis of two-dimensional (2D) and three-dimensional models (3D). Absorption near the fundamental edge was found to be due to indirect allowed transition on the basis of (3D) model and due to indirect forbidden transition on the basis of a (2D) model. Both transitions involve two phonons. The energy gaps and phonon energies have been estimated. The indirect and direct band gaps of WS x Se 2− x vary smoothly with the S/Se composition x, indicating that the nature of band edges is similar for WSe 2, WS 2 and compounds of intermediate composition. The dependence of band gaps on sulphur/selenium content in WS x Se 2− x has been adequately explained on the basis of band structure calculations reported in the literature.

Optical, dielectric and photoconductivity studies of bis(dimethylsulfoxide) tetrathiocyanato-cadmium(II) mercury(II) NLO single crystals

Nonlinear optical single crystals of bis(dimethylsulfoxide) tetrathiocyanato-cadmium(II) mercury(II), [CdHg(SCN)4(H6C2OS)2], (CMTD); a novel nonlinear optical material was conveniently grown from a DMSO–water mixed solvent by slow solvent evaporation technique. The grown crystals were characterized by single crystal X-ray diffractometry (XRD), FT-Raman, FT-IR and optical absorption spectrum. The microhardness test of the sample revealed that the crystal belong to the hard category of materials. The dielectric response of the crystal with varying frequencies was studied and reported. The photoconductivity studies confirmed the negative photoconducting nature of the crystal.

Effects of electron irradiation and subsequent annealing on the optical absorption and photoluminescence of CaF2 single crystals

Abstract The colorless transparent CaF2 single crystals turned blue after 1.7 MeV electron irradiation at fluences of 4 × 1016 and 1 × 1017 cm−2 at room temperature. The irradiated samples were annealed for 1 h at 70, 150, 200 and 300 °C in ambient atmosphere. Optical absorption and photoluminescence (PL) spectra were used to characterize the as-received, irradiated, and annealed crystals. Five obvious absorption bands peaked at 224, 339, 397, 579, and 800 nm, respectively, appear in the optical absorption spectra of the as irradiated samples. The absorption bands at 224, 339, and 800 nm disappear after annealing at 150 °C and the other two bands at 397 and 579 nm can still be observed even after annealing at 300 °C. A PL emission band at 422 nm is observed in the as-received crystals. The PL intensities of irradiated crystals gradually increase up to the level of the as-received samples with the increasing annealing temperature up to 300 °C.