Structural and vibrational properties of PVT grown Bi2Te3 microcrystals

High-quality Bi₂Te₃ microcrystals have been grown by physical vapor transport (PVT) method without using a foreign transport agent. The microcrystals grown under optimal temperature gradient are well facetted and they have dimensions up to ～100 μm. The phase composition of grown crystals has been identified by X-ray single crystal structure analysis in space group R3?m, a=4.3896(2) Å, b=30.5019(10) Å, Z=3 (R=0.0271). Raman microspectrometry has been used to describe the vibration parameters of Bi₂Te₃ microcrystals. The FWHM parameters obtained for representative Raman lines at 61 cm^?1 and 101 cm^?1 are as low as 3.5 cm^?1 and 4.5 cm^?1, respectively.     

Raman scattering in stage 1 europium intercalated graphite

The Raman spectrum of stage 1 europium intercalated graphite, EuC₆, has been recorded at room temperature. EuC₆ has a p(√3 × √3)R30° in-plane superlattice structure, the same as that of LiC₆. The c-axis stacking sequences of EuC₆ and LiC₆ are different. The Raman spectrum of EuC₆ exhibits a broad asymmetric Fano resonance peak at 1500 ± 5 cm^-1, similar to that observed in MC₈ (M = K, RbandCs). However, there is no evidence of any spectral feature around 580 cm^-1 as what has been observed in MC₈. Considering the Raman features of various graphite intercalation compounds in light of their superlattice structures, we suggest that: (1) The feature around 580 cm^-1 is a characteristic associated only with the MC₈p(2 × 2)R0° in-plane superlattice structure. It should originate from the M point phonons of pristine graphite, which become Raman active as predicted by phonon band structure calculations. (2) The continuous background in the spectra of EuC₆ and MC₈, which results in the Fano resonance peak at 1500 cm^-1, is associated with the staggered stacking sequence. Stacking faults are easy to occur in crystals with staggered stacking sequences, but not in crystals with complete elliptical sequences. Therefore, a disorder induced continuum is observed in the Raman spectra of EuC₆ and MC₈, but not in that of LiC₆.     

Structural and luminescence properties of Dy3+ ion in strontium lithium bismuth borate glasses

Different concentrations of dysprosium doped strontium lithium bismuth borate (SLBiB) glasses were synthesized by the conventional melt quenching method and characterized through X-ray diffraction, Raman, absorption and visible luminescence spectroscopies. These Dy³⁺ doped glasses are studied for their utility for white light emitting diodes. X-ray diffraction studies revealed amorphous nature of the studied glass matrices. Coexistence of trigonal BO₃ and tetrahedral BO₄ units was evidenced by Raman spectroscopy. From the absorption spectra, Judd–Ofelt (J–O) intensity parameters, Ω_λ (λ=2, 4 and 6), have been calculated. The hypersensitivity of the transition, ⁶H_15/2→⁶F_11/2 of Dy³⁺ has been discussed based on the magnitude of Ω₂ parameter. Using J–O intensity parameters, several radiative properties such as spontaneous transition probabilities (A_R), radiative branching ratios (β_R) and radiative lifetimes (τ_R) have been determined. From the emission spectra, a strong blue emission that corresponds to the transition, ⁴F_9/2→⁶H_15/2, was observed and it also shows combination of blue, yellow and red emission bands for these glasses. In addition to that, white light emission region have been observed from these studies.     

High resolution Raman spectroscopy of gases with laser sources. The rotational spectrum of cyanuric fluoride-C3N3F3

The pure rotational Raman spectrum of cyanuric fluoride vapor was photographed using a high resolution plane grating spectrograph. The spectrum was excited with the $\text{λ = 4880}\text{A}\text{?}$ radiation emitted by a single-mode argon-ion laser. Two sets of molecular constants were determined from the R and S branches. The preferred results are those determined from the S-branch data. These are: B₀ = 0.0655954 ± 14 × 10^?7 cm^?1, D_J = (2.52 ± 0.17) × 10^?9 cm^?1 and H_J = (?1.59 ± 0.59) × 10^?14 cm^?1, where the uncertainties are one standard deviation. Possible effects of line shifts due to unresolved K structure and the presence of hot bands on the accuracy of the values of the molecular constants are discussed. The B₀ value is compared to the rotation constant computed with the structural parameters determined with the electron diffraction technique; the agreement between these two rotation constants is only fair.     

The vapor-phase Raman spectra and the ring-puckering vibration of some deuterated analogs of trimethylene oxide

The ring-puckering vibration has been observed in the Raman spectra of the vapor phase of several deuterated species of trimethylene oxide (α - d₂, β - d₂, α, α′ - d₄, and d₆). Only Δv = 2 transitions have a measurable Raman intensity. The line positions agree with infrared values to better than 0.5 cm⁻¹ in most cases and better than 1 cm⁻¹ in all cases. For all molecules the interpretation of the spectra is consistent with an essentially planar configuration having only a small barrier to inversion.     

A possible interpretation of enhanced raman scattering in the vicinity of a nanotip

Theoretical and experimental studies on Raman scattering in a space with small bodies are briefly reviewed. Probabilities of radiative transitions for atoms (molecules) in the vicinity of bodies with dimensions much smaller than a wavelength are calculated. It is shown that in the vicinity of a nanosphere with |ε|?1, the probability of a single-photon electric dipole transition increases by a factor of 9, and the probability of a two-photon transition—by a factor of 81. In the vicinity of a conical needle resting on a plane (the needle and plane have |ε|?1), the radiative transition probability increases by a factor (λ/R _in)² and (λ/R _in)⁴ for single-and two-photon transitions, respectively (R _in is the radius of the needle tip curvature). This theoretical result is offered to interpret the enhancement of radiative processes experimentally observed in the referenced studies.     

Rotational Raman spectrum of cyclopropane

The pure rotational Raman spectrum of cyclopropane was observed up to J = 43. We have taken into account the effects of the unresolved K structure of the lines by assigning an effective value of K to the center of each unresolved line. Methods are developed for calculating effective K values for each value of J that allow a simultaneous fit to the R-and S-branch lines. The rotational constants of cyclopropane derived from this research are, in wavenumber units (cm^?1); B₀ = 0.6702₈, D_J = 1.0 × 10^?6, and D_JK = ?1.3 × 10^?6. We have also tested the validity of the method by using it with recent Raman data for BF₃.     

Influence of vapor transport equilibration on Raman spectra of Er:LiNbO3 crystals

Raman spectra of as-grown and vapor transport equilibration (VTE) treated Er:LiNbO₃ crystals, which have different cut orientations (X-cut and Z-cut), different Er-doping levels (Er:(0.2, 0.4 and 2.0 mol%)LiNbO₃) and different VTE durations (80, 120, 150 and 180 h), were recorded at room temperature in the wavenumber range 50-1000 cm⁻¹ by using backward scattering geometry. The spectra were attributed on the basis of their spectral features and the previous experimental work and the most recent theoretical progress in lattice dynamics on pure LiNbO₃. In comparison with the pure crystal the most remarkable effect of Er-doping on the Raman spectrum is observed for the E(TO₉) mode. It does not appear at 610 cm⁻¹ as the pure crystal, but locates at 633 cm⁻¹. In addition, the doping also results in the lowering of the Raman phonon frequency, the broadening of the Raman linewidth and the changes of the relative Raman intensity of some peaks. The VTE treatment results in the narrowing of the linewidth, the recovery of the lowered phonon frequency and the further changes of relative Raman intensity. The narrowing of Raman linewidth indicates that the VTE processing has brought these crystals closer to stoichiometric composition. The VTE treatment has induced the formation of a precipitate ErNbO₄ in the high-doped Er(2.0%):LiNbO₃ crystals whether X- or Z-cut. For these precipitated crystals, besides above linewidth and phonon frequency features, they also display more significant Raman intensity changes compared with those not precipitated crystals. In addition, a slight mixing between A₁(TO) and E(TO) spectra is also observed for these precipitated crystals. Above doping and VTE effects on Raman spectra were quantitatively or qualitatively correlated with the characteristics of the crystal structure and phonon vibrational system.     

Optical spectroscopy of low-dimensional rare-earth iron borates

The family of RFe₃(BO₃)₄ borates (R=Pr, Nd, Eu-Er, Y) was studied by high-resolution optical absorption and Raman spectroscopies. Structural and magnetic phase transitions were detected and the types of magnetic structure were determined. Energy of crystal-field (CF) levels and exchange splitting of the ground state of the R³⁺ ion were obtained from the analysis of optical spectra. CF calculations were carried out. Effective magnetic field at the R³⁺ site was found, using the calculated value of the magnetic g-factor. Some peculiarities of modeling the paramagnetic susceptibility of NdFe₃(BO₃)₄ are discussed.     

Quantitative analysis of chromate (CrVI) by normal Raman spectroscopy and surface-enhanced Raman spectroscopy using poly(diallyldimethylammonium) chloride-capped gold nanoparticles

Chromate (Cr^VI) has emerged as a widespread environmental contaminant found in groundwater and surface water, and there is a great need for rapid detection and monitoring of this contaminant. Normal Raman scattering (NRS) spectroscopy with a detection limit of Cr^VI at concentrations of 0.2 g/L was attached. And surface-enhanced Raman scattering (SERS) spectroscopy technique was found to be capable of detecting Cr^VI at concentrations as low as 2.5 mg/L using poly(diallyldimethylammonium) chloride modified gold nanoparticles (PDDA-AuNPs) as a substrate. The SERS substrate was successfully fabricated by combining the selfassembly technique with a heat-treatment-based strategy using poly(diallyldimethylammonium) chloride (PDDA) as the reducing and stabilizing agents. With the 520 cm^?1 band of silicon as internal standard, band intensity ratios of Cr^VI to silicon, that is I ₉₀₂/I ₅₂₀, were found to have a quantitative relationship with a large concentration range of Cr^VI from 0.2 to 20.0 g/L for NRS (R ² = 0.994) and from 2.5 to 25.0 mg/L for SERS (R ² = 0.980), respectively. Besides, the SERS methodology was reproducible, and susceptible to the interference of pH value. The optimum pH for Cr^VI detection by SERS was 3.38. The application of NRS and SERS showed high practical potential for rapid screening and routine analysis of Cr^VI in environmental samples.     

Specific features of the optical and electrical properties of polycrystalline CdTe films grown by the thermal evaporation method

The results of studying the physical properties of thin CdTe films obtained by the thermal evaporation method have been presented. The optical constants and the band gap of the films under study have been determined (E _g = 1.46 eV). It has been established based on the investigation of optical properties and the Raman spectrum of the films that they possess high structural quality. The activation energy of the electrical conductivity of CdTe films has been determined: E _a = 0.039 eV. The measured spectral dependences of the impedance of CdTe thin films are characteristic of the inhomogeneous medium with two time constants: τ_gb = R _gb C _gb = 1/ω_gb = 1.62 × 10^?3 s and τ_g = R _g C _g = 1/ω_g = 9.1 × 10^?7 s for grain boundaries and grains, respectively.     

Quantitative analysis of alcohol-water binary solutions using Raman spectroscopy

Raman spectroscopy was used for rapid and in situ measurements of alcohols in alcohol-water binary systems. An external standard was used to eliminate factors such as laser power or instrumental effects. Band ratios between the Raman bands of the target molecule and that of acetonitrile as external standard were calculated and found to be proportional to the mass fraction of alcohol. Better linearity was achieved as compared with that in the calibration curve obtained by plotting the Raman intensity alone. The equations of the calibration curves were y=0.2747x with R² of 0.9996 and y=0.2189x+1.340×10⁻³ with an R² of 1.000 in methanol-water and in ethanol-water binary systems, with y and x denoting the Raman intensity ratio and the mass fraction of alcohol, respectively.     

Synthesis, crystal structure, and spectroscopic study of K0.92(2) Zn0.08(2) H1.92(2) (PO4) (Zn-KDP)

The structure of K0.92₍₂₎ Zn_0.08(2) H_1.92(2) (PO₄) was determined using single-crystal X-ray diffraction. The crystal structure of the Zn-KDP belonged to the tetragonal space group $ \mathrm{I}\overline{4}2\mathrm{d} $ , with cell parameters of a?=?b?=?7.4487(5)?Å and c?=?6.9703(5)?Å, 386.73(5) Å3, Z?=?4, and R?=?0.023. Zn²⁺ ions were used as substitutes for K⁺ ions with hydrogen vacancy. The Zn-KDP single crystals were submitted to further Raman, infrared, and ¹H NMR studies to investigate chemical group functionalisation, possible bonding between the organic and inorganic materials, and partial substitution of K⁺ by Zn²⁺. The latter partial substitution was confirmed by the deviation of IR frequencies for O–H stretching, the variation of IR and Raman frequencies for stretching and bending vibrations ν(PO₄) of H₂PO₄, and the appearance of additional Raman (147, 386 and 481 cm^?1) vibrational bands. Electrical conductivity measurements were performed on polycrystalline pellets of Zn-KDP and pure KDP at room temperatures (RT) of up to 473K. In both cases, a conductivity jump close to 453K was observed, and a stronger increase of conductivity was measured.     

Multiphonon selection rules for cuprous oxide type crystalline systems

Experimental data on the IR and Raman spectra along with the slow coherent neutron scattering data for Cu₂O were examined for assignments of frequencies to phonon modes not only at the center but those at the boundary of the Brillouin zone. The inconsistency in assignments for the zone center modes and the lack of not only assignments but identifications of the zone boundary phonon required the use of second order Raman and IR spectra as the useful probes. The basis for the interpretation of these spectral data is given in terms of reduction coefficients for ordinary products and symmetrized squares and cubes of representations in the “cuprite” structure O_h⁴-Pn3m. They are presented for the R, X, M and Γ points of the Brillouin zone. They will serve for obtaining selection rules, invariants, and covariants for this structure. Additional tables are given that enable one to identify what pair of phonons correspond to electric dipole, magnetic dipole, electric quadrupole, or Raman transitions, respectively.     

The vapor phase Raman spectra,Raman band contour analyses,Coriolis constants,force constants,and values for thermodynamic functions of the trihalides of group V

The vapor phase Raman spectra have been recorded of the molecules PX₃ (X = F, Cl, or Br), AsX₃ (X = F, Cl, Br, or I), and SbX₃ (X = Cl, Br, or I) in sealed tubes at 22–365°C as appropriate. Attempts to record the vapor phase Raman spectra of the molecules PI₃, SbF₃, and BiX₃ (X = F, Cl, Br, or I) were unsuccessful. The infrared and Raman rotational branch separations of the a₁ species fundamentals for these molecules are in agreement with the theoretically calculated values. The Raman band contours of the e-species fundamentals have been analyzed to yield, in favorable cases, values for the corresponding Coriolis constants which have been compared with those obtained from infrared band contour analyses, and which have been employed to constrain the e-species force constants. It is concluded that the Raman contour method for defining Coriolis and thus force constants should be regarded as further, but not necessarily the best, experimental method with which to help to constrain the field. Values for various thermodynamic functions of the molecules have been calculated from the new values for the fundamental frequencies and from the most recent structural data.     

Theoretical assignment of the observed hyperfine structure in the saturated absorption spectra of I2129 and I127I129 vapors in the 633 nm wavelength region

The detailed structure observed in the saturated absorption spectrum of I₂¹²⁹ vapor in the 633 nm wavelength region in the spectral interval reported by Knox and Pao, has been interpreted to be the overlap between the hyperfine lines of the 8-4 P(54) line of I₂¹²⁹ and the 6-3 P(33) line of the I¹²⁷I¹²⁹ vapor. In this assignment, the nuclear electric quadrupole and nuclear magnetic terms in the Hamiltonian were diagonalized exactly and certain molecular parameters were varied to obtain the best fit with the observed spectrum. For I₂¹²⁹, the calculated distance (separation) of the center of the 8-4 P(54) line from the line center of the Ne²⁰ 633 nm laser transition is 0.04 cm^?1 and the RMS deviation between the theoretical and experimental hyperfine spectra is 0.3 MHz. Although the calculated frequency of R(60) transition in the 8-4 band is only 0.03 cm^?1 from the center of the laser line, we conclude on the basis of the larger RMS error (0.5 MHz) that this latter transition is less likely to be that responsible for the structure discussed in this paper.     

Evidence for non-thermal excitation of energy levels in active biological systems

The ratio R of the intensities of anti Stokes and Stokes Raman shift lines of 124 cm^-1 and of 118 cm^-1 of active E. coli B was measured. For an oscillating system in therm equilibrium R ≈ 0.55 is expected whereas we find R ≈ 1.0. This shows that this system is excited strongly above thermal excitation in agreement with a previous theoretical conjecture [2–5].     

Spectrofluorometric investigation of salicylal- dithiocarbazinic acid esters

The fluorescent properties of salicylaldithiocarbazinic esters which can be described by RR¹C= N-NH-CSSR² (where R = 0HO-C₆H₄; R¹ = H or CH₃; R² =CH₃, C₆H₅-CH₂ or p-C1-C₆H₄-CH₂) have been investigated.The investigations were made in DMF, in different DMF-water mixtures, and in aqueous media. It could be stated that the change of the R² group has an unimportant effect on the intensity of fluorescence and on the excitation and emission spectra in all examined solvents. But an important effect is caused by the change of the group R¹. As in DMF solution, only the excitation spectrum changes on substituting R¹ = H by R¹ = CH₃, in DMF: water i.e. aqueous media, the change in the intensity of fluorescence, too, is very great.In the case of R¹ = H, the intensity of fluorescence is about five times greater than in R¹ = CH₃. The intensity of fluorescence can be increased, if an electrophil substituent is put into the place of group R¹.     

The microwave,Raman, far infrared,and NMR spectra and structure of methylchloroformate

The microwave spectra of six isotopic species of methylchloroformate, ClCO₂CH₃, have been recorded from 18.0 to 40.0 GHz. Structural parameters have been determined, and it is shown that the only stable conformer at ambient temperature is the s-trans. The Raman and far infrared spectra of the vapor are reported. Four cases of Fermi resonance have been observed in the Raman effect. Both the methyl and methoxy torsions have been observed in the far infrared, and the methyl barrier to internal rotation has been determined to be 1.15 kcal/mole (1.19 kcal/mole for the CD₃ rotor), which is in agreement with the 1.23 kcal/mole obtained from the microwave splitting method. It is shown from both the ¹³C and ¹H NMR spectra along with the far-infrared data that only one conformer exists, which is contrary to what was previously reported. The vibrational spectrum of the solid is also reported and discussed.     

Semiempirical calculation of the absolute solvation shift of electronic and vibrational spectra of molecules in the gas-solution phase transition

Calculations of the main components of the absolute solvation shift of Δυ _∑ ^{a, f, R} optical absorption, emission, and Raman spectra of molecules in the gas-solution phase transition for solutions of several diatomic (HCl, DCl, H₂, D₂) and polyatomic (anthracene, 3-and 4-aminophthalimide) substances in some polar and nonpolar solvents are presented. The calculations are made by a new method of the semiempirical theory, which was proposed by the author earlier and makes such calculations possible for the first time. It is shown that the given theory adequately describes the photophysical effect under study and provides a correct prediction of the values of Δυ _∑ ^{a, f, R} , which differ for different systems by more than three orders of magnitude (from several inverse centimeters for vibrational spectra of H₂ and D₂ to many thousands of inverse centimeters for electronic fluorescence spectra of solutions of aminosubstituted derivatives of phthalimide).