Absorption Of Single Crystals Research Articles

Preparation, single-crystal investigation and spectrophotometric studies of proton transfer complex of 2,6-diaminopyridine with oxalic acid in various polar solvents

Charge transfer complex (CT complex) of donor, 2,6-diaminopyridine (DAP) and π- acceptor, oxalic acid (OA) has been synthesized in acetonitrile at room temperature. The CT complex is formed through the transfer of lone pair electrons from 2,6-diaminopyridine to oxalic acid. The CT complex was characterized by elemental analysis, FTIR spectra single crystal studies, TGA-DTA, 1H NMR and electronic absorption spectra in different solvents which indicate the CT interaction associated with proton migration from the acceptor to the donor followed by hydrogen bonding via N+H⋯O−. It was found that formation of CT Complex is solvent dependent. Spectrophotometric data show the properties of complex in terms of formation constant (KCT), molar extinction coefficient (εCT), energy of interaction (ECT), ionization potential (ID), resonance energy (RN), free energy (ΔG), oscillator strength (f) and transition dipole moment (μEN). The stoichiometry of the CT complex was found to be 1:1 by a straight-line method between donor and acceptor with maximum absorption bands. The physical parameters of CT complex were evaluated by the Benesi–Hildebrand equation. The agreements between the spectroscopic results were also confirmed by single crystal X-ray of the resulting charge transfer complex.

Thin single crystal perovskite solar cells to harvest below-bandgap light absorption

The efficiency of perovskite solar cells has surged in the past few years, while the bandgaps of current perovskite materials for record efficiencies are much larger than the optimal value, which makes the efficiency far lower than the Shockley–Queisser efficiency limit. Here we show that utilizing the below-bandgap absorption of perovskite single crystals can narrow down their effective optical bandgap without changing the composition. Thin methylammonium lead triiodide single crystals with tuned thickness of tens of micrometers are directly grown on hole-transport-layer covered substrates by a hydrophobic interface confined lateral crystal growth method. The spectral response of the methylammonium lead triiodide single crystal solar cells is extended to 820 nm, 20 nm broader than the corresponding polycrystalline thin-film solar cells. The open-circuit voltage and fill factor are not sacrificed, resulting in an efficiency of 17.8% for single crystal perovskite solar cells.

Optical absorption and photoconductivity of MnGaInS4 single crystals in polarized light

The results of studying optical-absorption and spectral curves of photoconductivity in MnGaInS4 single crystals are presented for two light polarizations (E || C and E ⊥ C). The intrinsic absorption edge and the band-gap width of MnGaInS4 single crystals in polarized light are determined. The anisotropy of optical absorption and photoconductivity spectrum of MnGaInS4 single crystals is observed. It is suggested that the polarization splitting of the absorption edge is related to the splitting of the MnGaInS4 valence band.

Vibronic exciton theory of singlet fission. I. Linear absorption and the anatomy of the correlated triplet pair state.

Recent time-resolved spectroscopic experiments have indicated that vibronic coupling plays a vital role in facilitating the process of singlet fission. In this work, which forms the first article of a series, we set out to unravel the mechanisms underlying singlet fission through a vibronic exciton theory. We formulate a model in which both electronic and vibrational degrees of freedom are treated microscopically and non-perturbatively. Using pentacene as a prototypical material for singlet fission, we subject our theory to comparison with measurements on polarization-resolved absorption of single crystals, and employ our model to characterize the excited states underlying the absorption band. Special attention is given to the convergence of photophysical observables with respect to the basis size employed, through which we determine the optimal basis for more expensive calculations to be presented in subsequent work. We furthermore evaluate the energetic separation between the optically prepared singlet excited state and the correlated triplet pair state, as well as provide a real-space characterization of the latter, both of which are of key importance in the discussion of fission dynamics. We discuss our results in the context of recent experimental studies.

One-Pot Synthesis of a Mono-O,B,N-strapped BODIPY Derivative Displaying Bright Fluorescence in the Solid State.

Tin(IV) catalysis allows isolation of a boron dipyrromethene derivative bearing a solitary strap around the boron center. The conditions favor internal cyclization without contamination by side products and provide high yields of product in good purity. A phenolate-based strap imposes chirality and causes geometrical distortion of the dipyrrin. Relatively strong fluorescence is observed for single crystals, evaporated films, and adsorbed layers. Single-crystal absorption and emission spectra resemble those observed from solution with contributions from a dimer.

Some IR features of SiO4 and OH in coesite, and its amorphization and dehydration at ambient pressure

Coesite (Coe) with grain size in the range of 30–80μm has been synthesized at 5GPa and 1600°C for 12h by using a cubic press. Its unpolarized single-crystal absorption infrared (IR) spectra show 14 IR bands in the range of ∼1200–650cm−1, five of which have high intensity (at ∼1161, 1109, 1063, 1028 and 994cm−1) and are preliminarily assigned to the SiO4 asymmetric stretching (ν3). In addition, three sharp but relatively weak bands at ∼838, 814 and 796cm−1 are tentatively attributed to the SiO4 asymmetric bending (ν4). The IR data also show six OH peaks in the range of 3700–3300cm−1, with an estimated H2O content of ∼30(4)wt ppm. Following previous studies, we have assigned the peaks at ∼3464 (#7), 3421 (#8), 3406 (#9) and 3377cm−1 (#10) to the Type-II hydrogarnet substitution, and the peaks at ∼3500 (#6a) and 3534cm−1 (#6b) to the B-based defects, with the latter aroused by possible B contamination in the synthesizing experiments. Annealing experiments conducted consecutively at ∼200, 400, 600, 800, 1000 and 1200°C, with every heating step lasting for 24h, demonstrate that water diffuses quickly out of Coe at T as low as ∼600°C. The material annealed at 1200°C is completely dehydrated and amorphous. A quick response of the water content in Coe to the changes of P, T and composition is thus possible, which may be critical to the preservation of natural Coe in relevant geological processes. It further implies that water in Coe, and possibly in other nominally anhydrous minerals (NAMs), may behave distinctively different from the water located in the hydrous phases such as amphibole and mica, and potentially makes significant contribution to the subduction zone-related fluids.

Effect of Nd Impurity on Photoconductivity and Optical Absorption Spectra of GeS Single Crystal

The effect of Nd impurities on the mechanism of photoconductivity and light absorption in GeS single crystals was investigated. The structure of the spectra was studied, and the exciton states and the energy of direct and indirect band–band transitions were investigated.

High resolution x-ray absorption and emission spectroscopy of LixCoO2 single crystals as a function delithiation

The effect of delithiation in LixCoO2 is studied by high resolution Co K-edge x-ray absorption and x-ray emission spectroscopy. Polarization dependence of the x-ray absorption spectra on single crystal samples is exploited to reveal information on the anisotropic electronic structure. We find that the electronic structure of LixCoO2 is significantly affected by delithiation in which the Co ions oxidation state tending to change from 3+ to 4+. The Co intersite (intrasite) 4p–3d hybridization suffers a decrease (increase) by delithiation. The unoccupied 3d t2g orbitals with a1g symmetry, containing substantial O 2p character, hybridize isotropically with Co 4p orbitals and likely to have itinerant character unlike anisotropically hybridized 3d eg orbitals. Such a peculiar electronic structure could have significant effect on the mobility of Li in LixCoO2 cathode and hence the battery characteristics.

Near infrared photodetectors based on sub‐gap absorption in organohalide perovskite single crystals

AbstractOrganohalide perovskite optoelectronics based upon large (mm‐sized) single crystals present exciting opportunities for new device platforms and fundamental studies. Herein, we report CH3NH3PbBr3 and CH3NH3PbI3 single crystals prepared via an inverse temperature crystallization method with strong near infrared photoresponses significantly below the optical gap. Light intensity dependent photocurrent measurements reveal the photoresponse is not a two‐photon phenomenon, but rather is derived from a linear mechanism. The effect (including responsivity and speed) is enhanced in a photoresistor architecture, indicating that the photoresponse is due to absorption into surface trap states in the crystal. Without any optimisation, respectable NIR responsivities at room temperature of ∼10‐2 A W−1 at a low 1V bias operating voltage are achieved. These results again demonstrate the remarkable potential of organohalide perovskites as light sensing materials, and the possibilities for engineering a new class of single crystal‐based optoelectronics. image

Observation of Two-Photon Absorption and Nonlinear Refraction in AlN**Supported by the National Natural Science Foundation of China under Grant Nos 51372267, 51210105026 and 51172270, and the National Basic Research Program of China under Grant No 2013CB932901.

Two-photon absorption (TPA) and nonlinear refraction in AlN single crystals are revealed with the single beam Z-scan technique. A large TPA coefficient of 13±3cm/GW at 355nm and third-order nonlinear refractive indices of −1.91±0.38×10−13 cm2/W at 355 nm, 1.79±0.36×10−13 cm2/W at 532 nm and 1.61±0.32×10−12 cm2/W at 1064 nm are derived. It is inferred that the TPA-generated free carriers are responsible for the large negative nonlinear refractive index at 355 nm, while the oxygen impurity induced bandgap narrowing may account for the large third-order nonlinear refractive indices at 532 nm and 1064 nm. The large nonlinear optical responses of AlN promise wide applications in the deep ultraviolet nonlinear optical devices.

Polarized optical absorption of MnGa2S4 single crystals

Optical absorption of MnGa2S4 single crystals is studied at two light polarizations (E ||C and E⊥ C). The polarization splitting of the absorption edge points to a splitting of the valence band of MnGa2S4. A contribution to the crystal-field splitting is made by two factors, namely, by a difference in the pseudopotential of cationic sublattice atoms and by tetragonal compression of the lattice along the C axis. A scheme of optical transitions in MnGa2S4 in the Brillouin zone center is suggested, according to which the optical transitions Г3 + Г4 → Г1 occur in the polarization E ⊥ C, and the Г2 → Г1 transitions occur in the polarization E || C.

Self-polarized terahertz magnon absorption in a single crystal ofBiFeO3

We report the polarization dependence of terahertz magnon absorption in single crystals of ${\mathrm{BiFeO}}_{3}$ grown by a modified floating zone method. In a (111)${}_{\mathrm{pc}}$-oriented crystal, two major magnon absorption signals were observed for all terahertz polarizations, which indicates that magnetic domains were not aligned in one of the three allowed directions. In contrast, the absorption modes in a (001)${}_{\mathrm{pc}}$-oriented crystal showed significant polarization dependence, which was unchanged even after annealing the crystal at temperatures far above the N\'eel point to demagnetize it. This polarization dependence coincides with that of $E$ mode phonons. Thus, we conclude that magnon and phonon in ${\mathrm{BiFeO}}_{3}$ are strongly coupled and the selection rules for magnon absorption are governed by the activity of $E$ mode phonons, namely, the crystalline anisotropy originating from ferroelectric polarization.

Assembly of organic moiety with metal-oxide cluster to generate a new three dimensional supramolecular/hydrogen bonded network based on isopolymolybdate

A new octa-molybdate formulated as (C2H6N4)2 [β-Mo 8 O 26].4H 2O (1) has been isolated by conventional solution method and structurally characterized by single-crystal X-ray diffraction method, IR spectroscopy, UV-Vis absorption, thermogravimetric analysis and cyclic voltammetry. Compound 1 crystallizes in the Triclinic system, space group P-1 with unit cell dimensions, a = 8.348 (2) Å, b = 10.154 (2) Å, c = 10.823 (3) Å, α=68.35∘ (2), β=71.59∘ (2), ɤ =78.55∘ (2), V = 805.5 (3) Å 3, and Z = 2. The crystal structure of 1 is built up from octa-molybdate [ β-Mo 8 O 26] 4− clusters connected through hydrogen-bonding interactions into a three-dimensional supramolecular network. A new organic–inorganic hybrid material was prepared from ammonium hepta-molybdate in acidic medium by addition of 1, 2, 4-triazol-3-amine to obtain an octa-molybdate formulated as (C2H6N4)2 [β-Mo8O26].4H2O. The compound was characterized by single crystal X-ray diffraction method, IR spectroscopy, UV-Vis absorption, thermogravimetric analysis and cyclic voltammetry.

Single crystal growth and polarization absorption spectroscopy of theophylline anhydrous for terahertz vibrational mode assignment

In an attempt to provide a procedure for mode assignment in the terahertz (THz) frequency range, we fabricated an apparatus for single crystal growth via a temperature difference method to provide organic crystals that are sufficiently thin for wide-range THz transmission spectroscopy.Single-crystal theophylline anhydrous (TPAH) was successfully fabricated. THz polarization spectroscopy measurements were performed on TPAH crystal samples at 70K. Assignment of the absorption peaks was carried out by comparing measurement results with those from density functional theory (DFT) calculations under periodic boundary conditions.

(Invited) Anisotropic Magnetism of an Endohedral Metallofullerene for Molecular Location Sensor

Location recognition in molecular-scale provides valuable information on positional relationship, absolute conformation and dynamics of molecules. They can be used for deep understanding of nature of functional molecular materials or for elucidating biological processes. Therefore, a number of molecular probes have been developed and reported to date for molecular recognition and location determination. Recently, our group has reported anisotropic magnetism of an endohedral metallofullerene (EMF) Ce@C82 both in a pristine form and chemically functionalized form.1,2 Remarkably, the anisotropy of the magnetism which is led by the encapsulated Ce atom was slightly influenced by the carbene addition reaction. In addition, absolute position of the hydrogen atoms of the addend were assigned by the difference in the effective distance of the anisotropic magnetism, which is decreased with the cube of distance between the Ce and hydrogen atoms. In this study, we have developed Ce@C82 derivatives that demonstrate a potential of EMFs for location recognition in molecular-scale. Five derivatives of Ce@C82 were successfully synthesized and isolated by a similar radical reaction that we reported recently.3 Addition position of the two isomers of them were unambiguously determined by a single crystal structure and/or characteristic absorption spectra. DFT calculations provide reasonable criteria to predict the addition position by the radical coupling reaction. The carbon atoms that have high SOMO density and positive charge are preferable for the addition position. Temperature-dependent 1H-NMR measurements demonstrated unique paramagnetic shifts that are derived by the anisotropic magnetism of the Ce atom. And further analysis of the shifts revealed the dependency of the shift based on the distance and relative position from the Ce atom. This result indicates that the paramagnetic shifts provide location information of the addend. Therefore, Ce@C82 is capable to act as an molecular probe for location recognition of atoms by utilizing anisotropic magnetism of an EMF. Reference: 1. T. Wakahara et al. J. Am. Chem. Soc. 2004, 126, 4883-4887. 2. Y. Takano et al. J. Am. Chem. Soc. 2009, 131, 9340-9346. 3. Y. Takano et al. J. Am. Chem. Soc. 2008, 130, 16224-16230.

UV-Visible Absorption Spectroscopy Enhanced X-ray Crystallography at Synchrotron and X-ray Free Electron Laser Sources.

This review describes the use of single crystal UV-Visible Absorption micro-Spectrophotometry (UV-Vis AS) to enhance the design and execution of X-ray crystallography experiments for structural investigations of reaction intermediates of redox active and photosensitive proteins. Considerations for UV-Vis AS measurements at the synchrotron and associated instrumentation are described. UV-Vis AS is useful to verify the intermediate state of an enzyme and to monitor the progression of reactions within crystals. Radiation induced redox changes within protein crystals may be monitored to devise effective diffraction data collection strategies. An overview of the specific effects of radiation damage on macromolecular crystals is presented along with data collection strategies that minimize these effects by combining data from multiple crystals used at the synchrotron and with the X-ray free electron laser.

Quinolinium-based organic electro-optic crystals: Crystal characteristics in solvent mixtures and optical properties in the terahertz range

We investigate crystal characteristics of ionic organic π-conjugated crystals based on 4-hydroxy-3-methoxystyryl quinolinium (HMQ), which are recently developed acentric crystals showing a large nonlinear optical response and a high THz generation efficiency. Among a few of HMQ derivatives, HMQ-T crystal consisting of the HMQ cation and the 4-methylbenzenesulfonate anion, is chosen for the investigation of solubility, morphology and crystal growth characteristics including optical properties in various single solvents and solvent mixtures. Compared to the solvent mixture of non-aromatic methanol and acetonitrile, HMQ-T crystals in a solvent mixture containing an aromatic solvent (methanol/toluene mixture) exhibits a similar solubility variation with the solvent composition ratio, but based on distinguishable intermolecular interactions with solvent molecules. In addition, solvent mixtures containing an aromatic solvent show a significantly different equilibrium between benzenoid and quinoid forms of the HMQ cation. In contrast to the strong influence of solvent characteristics on solubility behavior, the investigated solvent systems only slightly influence the crystal morphology. Large HMQ-T single crystals with size up to 37 × 6 × 2 mm3 are grown by slow cooling method. We also determine the refractive index and absorption of as-grown single HMQ-T crystals in the broad THz frequency range of 0.3–10 THz.

Synthesis and thermal, optical, dielectric and mechanical properties of l-asparagine sodium nitrate single crystal

Single crystal of l-asparagine sodium nitrate (LASN) was grown from aqueous solution by room temperature solution growth technique. The grown crystal was characterized by single crystal X-ray diffractometry (XRD), FTIR and optical absorption spectrum. The micro hardness test of the sample revealed that the crystal belongs to the soft category of materials. The dielectric response of the crystal with varying frequencies was studied and reported. The thermal stability of the compounds has been determined by TG-DTA curves. The SHG relative efficiency of LASN crystal was found to be inferior than that of KDP.

Mechanical detection of electron spin resonance beyond 1 THz

We report the cantilever detection of electron spin resonance (ESR) in the terahertz (THz) region. This technique mechanically detects ESR as a change in magnetic torque that acts on the cantilever. The ESR absorption of a tiny single crystal of Co Tutton salt, Co(NH4)2(SO4)2⋅6H2O, was observed in frequencies of up to 1.1 THz using a backward travelling wave oscillator as a THz-wave source. This is the highest frequency of mechanical detection of ESR till date. The spectral resolution was evaluated with the ratio of the peak separation to the sum of the half-width at half maximum of two absorption peaks. The highest resolution value of 8.59 ± 0.53 was achieved at 685 GHz, while 2.47 ± 0.01 at 80 GHz. This technique will not only broaden the scope of ESR spectroscopy application but also lead to high-spectral-resolution ESR imaging.

Study on a series of rhenium complexes: Synthesis, characterization, photophysical feature and oxygen sensing performance

This paper synthesized a series of diamine ligands with different conjugation chains and their corresponding Re(I) complexes for oxygen sensing purpose. It was anticipated that these conjugation chains might increase sensing collision probability and thus improve sensing performance. These Re(I) complexes were characterized in detail, including their single crystal structures, electronic transitions, absorption and emission spectra, emission lifetimes and yields. By doping them into a silica substrate MCM-41, their emission response to various O2 concentrations was analyzed. A maximum emission intensity ratio of 8.17 was obtained with short response time of 7s. The correlation between sensing performance and probe structure was discussed tentatively. We finally came to a conclusion that excited state lifetime was a major factor controlling sensitivity. While electron distribution effect on sensitivity was limited.