Study of lattice vibrational modes in CuGaS2 by using fourier transform spectroscopy

The lattice dynamics of a single crystal of CuGaS₂, grown by iodine transport technique, have been studied by using far IR absorption spectroscopy. All the absorption maxima caused by the phonon excitation are compared with the lattice vibrational modes obtained by Raman spectroscopy and by IR reflection techniques. An absorption maximum located at 175 cm^?1 cannot be explained with the help of phonon excitation; however this peak can be attributed to the defect frequency originating from the replacement of gallium atom by sulphur in the v₁₇ mode of vibration. The frequency of this defect-induced vibrational mode is calculated by taking a modified molecular model approach, and is found to be 166.9 cm^?1, which is in reasonably good agreement with the experimentally observed value of 175 cm^?1.     

Acoustical phonon anomaly in the Raman spectra of intermediate valent TmSe1−xTex and TmxSe

In the Raman spectra of intermediate valent TmSe_1?xTe_x the same anomaly within the acoustical phonon band at 60 cm^?1 is found as in Tm_xSe. The connection of this anomaly with the valence mixing is confirmed. In a one-dimensional model calculation it is shown that a renormalized LA dispersion curve can produce the observed anomalous peak in the phonon DOS. As an alternative interpretation the possibility of a low energy electronic excitation at 60 cm^?1 is discussed.     

Raman study of charge-density-wave phase transition in quasi-one-dimensional conductor (TaSe4)2I

Polarized Raman spectra were obtained in the quasi-one-dimensional conductor (TaSe₄)₂I above and below the charge-density-wave (CDW) transition temperature (T_c=263 K). The Raman intensities of many peaks become intenser and two of the phonon peaks shift to higher frequency with decreasing temperature. Moreover a new broad peak at about 90 cm^?1 and a new peak around 166 cm^?1 appear in the low-temperature phase. The polarization characteristic shows that the former is assigned to totally symmetric mode. The damping constant of the phonon at 90 cm^?1 increases markedly with increasing temperature. The frequency shifts to higher frequency as the temperature increases and the coupling coefficient is approximately proportional to (T_c?T)^{$\text{1}\text{2}$}. This peak becomes Raman active owing to the CDW phase transition. The temperature dependence of the damping constant and the frequency shift may have a relation to the dynamical properties of the CDW phase transition.     

Raman study of BiFeO3 with different excitation wavelengths

Raman spectra of bismuth ferrite (BiFeO₃) over the frequency range of 100-1500 cm⁻¹ have been systematically investigated with different excitation wavelengths. The intensities of the two-phonon modes are enhanced obviously under the excitation of 532 nm wavelength. This is attributed to the resonant behavior when incident laser energy closes to the intrinsic bandgap of BiFeO₃. The Raman spectra of BiFeO₃ excited at 532 nm were measured over the temperature range from 77 to 678 K. Besides the abnormal changes of the peak position and the linewidth of the A₁ mode at 139 cm⁻¹, the prominent frequency shift, the line broadening and the decrease of the intensity for the two-phonon mode at 1250 cm⁻¹ were observed as the temperature increased to Néel temperature (T_N). All these results indicate the existence of strong spin-phonon coupling in BiFeO₃.     

Antiresonance of Raman cross-sections for nonpolar phonons in CdS

The nonpolar optic phonons of E₂ symmetry in CdS are shown to exhibit a pronounced decrease in Raman cross-section at certain excitation energies. For the E₂ phonon branch at 43 cm⁻¹ the minimum cross-section occurs for laser excitation ∼0.18 eV below the band gap, and cross-section vs. excitation energy near this antiresonant minimum can be described by an equation of the form used by Ralston et al. for transverse polar phonon cross-sections. For the E₂ mode at 256 cm⁻¹ the antiresonance occurs at wavelengths longer than 6328 Å.     

Raman excitation profiles of adsorbates at roughened silver surfaces

The excitation profiles of Raman bands of pyridine (1008 cm^?1), triphenylphosphine (997 cm^?1), [CN]^? (2114 cm^?1), and [Ru₃O₂(NH₃)₁₄]⁶⁺ (ruthenium red, 275 cm^?1) adsorbed at roughened silver-aqueous interfaces have been measured over the range 458–799 nm. Apart from [CN]^? for which experimental limitations prevented measurements with excitation in the far red, each of the adsorbates shows a pronounced excitation profile maximum for excitation in the range 590–750 nm. Measurements on triphenylphosphine at a silver-aqueous interface and on the same silver surface in gaseous nitrogen detected some difference in the excitation profiles due to change of medium. These results are discussed in relation to various theories of enhanced Raman scattering by adsorbates at metal surfaces.     

Studies on the complex behavior of optical phonon modes in wurtzite (ZnO)1−x (Cr2O3) x

This paper reports on the use of phonon spectra obtained with laser Raman spectroscopy for the uncertainty concerned to the optical phonon modes in pure and composite ZnO_1?x (Cr₂O₃) _x . Particularly, in previous literature, the two modes at 514 and 640 cm^?1 have been assigned to ZnO are not found for pure ZnO in our present study. The systems investigated for the typical behavior of phonon modes with 442 nm as excitation wavelength are the representative semiconductor (ZnO)_1?x (Cr₂O₃) _x (x = 0, 5, 10 and 15 %). Room temperature Raman spectroscopy has been demonstrated polycrystalline wurtzite structure of ZnO with no structural transition from wurtzite to cubic with Cr₂O₃. The incorporation of Cr³⁺ at most likely on the Zn sub-lattice sites is confirmed. The uncertainty of complex phonon bands is explained by disorder-activated Raman scattering due to the relaxation of Raman selection rules produced by the breakdown of translational symmetry of the crystal lattice and dopant material. The energy of the E ₂ (high) peak located at energy 53.90 meV (435 cm^?1) due to phonon–phonon anharmonic interaction increases to 54.55 meV (441 cm^?1). A clear picture of the dopant-induced phonon modes along with the B ₁ silent mode of ZnO is presented and has been explained explicitly. Moreover, anharmonic line width and effect of dislocation density on these phonon modes have also been illustrated for the system. The study will have a significant impact on the application where thermal conductivity and electrical properties of the materials are more pronounced.     

High resolution Raman spectroscopy of the fundamental vibrational band of 16O2

The vibrational Raman spectrum of ¹⁶O₂ has been recorded with high resolution (0.05 cm^?1 for the Q branch). The expansion of the Hamiltonian as a sum of irreducible tensors of the O(3) group allowed us to obtain easily the expressions for the energy levels, taking into account the off-diagonal matrix elements. From the analysis of the spectrum the excited state constants have been calculated; in particular the rotational constants obtained are: B₁ = 1.421884 ± 0.000013 cm^?1 and D₁ = (?4.864 ± 0.014)10^?6 cm^?1.     

Observation of a soft phonon in linear chain compound (NbSe4)3I by Raman scattering

The phase transition of the linear chain compound (NbSe₄)₃I was studied by Raman scattering. At 78 K three new peaks were observed at 73 cm^?1, 205 cm^?1 and 261 cm^?1. The totally symmetric Raman peak at 73 cm^?1 shows anomalous temperature dependence. The frequency decreases with increasing temperature, and at high temperatures an anticrossing occurs with another peak observed at about 58 cm^?1. The Raman intensity decreases and the linewidth broadens remarkably as the temperature increases. These properties allow us to assign this peak to a soft phonon. This fact indicates clearly the existence of a structural phase transition of a displacive type below room temperature.     

Raman scattering in FeF3

Peaks in the FeF₃ phonon Raman spectrum are assigned to the A_1g(312 cm^-1) and E_g(105, 187, 450 cm^-1) representations of the D⁶_3d group. Anomalous temperature dependence of the frequency, intensity and line width of the 187 cm^-1 line has been observed.     

Raman scattering in K2Pt(CN)4Br0.3 · 3H2O

Raman scattering experiments on K₂Pt(CN)₄Br_0.3 · 3H₂O are reported between 5 and 300 K as a function of temperature. A line of A₁ symmetry detected at 44 cm^?1 shows interesting temperature dependent properties. It is concluded from a comparison of the frequency, symmetry, and scattering intensity of this line with theoretical predictions that the excitation concerned represents the amplitude mode of the charge density wave (the line observed in infrared absorption being the phase mode). No Peierls transition is observed, but the results are consistent with a Peierls distortion present at all temperatures. The findings are correlated with inelastic neutron scattering and infrared studies. Finally, the CN stretching modes at 2189 and 2173 cm^?1 and the water mode at 3490 cm^?1 are studied as a function of temperature.     

Raman scattering study of the dynamics of the pressure-induced phase transition in thallium azide (TlN3)

A Raman scattering investigation of the pressure-induced phase transition in tetragonal thallium azide (TlN₃) is reported. The most interesting features of the Raman spectrum of TlN₃ are the anti-resonant line-shapes of two E_g symmetry phonons at 35 and 50 cm^?1 superimposed on a quasi-elastic wing. The scattering data is shown to be consistent with a model in which the two phonons interact via an imaginary coupling term. The phonon at 35 cm^?1 (assigned to a translational shear mode of the Tl⁺ sublattice) softens with increasing pressure and increases in linewidth as P approaches P₀ (=8 kbar) from below. At the same time, the quasi-elastic scattering component (associated with large amplitude N₃^? librational fluctuations) becomes less damped. A displacive structural transition from tetragonal to monoclinic is indicated by the eigenvector of the soft phonon.     

Excitation spectra and fluorescent lifetime measurements of Mn2+ in CaF2 and CdF2

The excitation spectrum of the Mn²⁺ emission has been measured in CaF₂ and CdF₂. The observed excitation bands have been assigned to transitions of the Mn²⁺ ions in a cubic environment. The calculated values for the crystal field (Dq) and Racah parameters (B,C) are Dq = 425 cm^-1 for CaF₂, Dq = 500 cm^-1 for CdF₂ and, B = 770 cm^-1 and C / B = 4.48 for both compounds. The lifetime of the fluorescent level ⁴T_1g(⁴G) has been measured in both compounds at different temperatures in the range from 10 to 500 K. The lifetime thermal dependence is explained taking into account different mechanisms (purely radiative, phonon assisted, and radiationless transitions) for the decay of excited Mn²⁺ ions.     

Determination of A0 for CH335Cl and CH337Cl from the ν4 infrared and Raman bands

The ν₄ infrared and Raman bands of CH₃Cl were analyzed simultaneously. A direct fit yielded a complete set of constants for CH₃³⁵Cl, including A₀ = 5.20530 ± 0.00010 cm^?1 and D_K = (8.85 ± 0.13) × 10^?5cm^?1. For CH₃³⁷Cl an incomplete set of constants was obtained from the infrared band, and A₀ = 5.2182 ± 0.0010 cm^?1 was estimated by curve fitting of the Raman spectrum. The resulting equilibrium structure is $\text{r(}\text{CH) = 1.0854 ± 0.0005}\text{A}\text{?}$, $\text{r(}\text{CCl) = 1.7760 ± 0.0003}\text{A}\text{?}$, and <(HCH) = 110°.35 ± 0°.05.     

Fluorescence spectra of matrix-isolated Se2

Laser induced fluorescence spectra are reported for samples of natural selenium and of the separated ⁷⁸Se and ⁸⁰Se isotopes in Ar and Kr matrices. The B(0_u⁺) → X(0_g⁺) and B(1_u) → X(1_g) systems of Se₂, already known in the gas, are observed by both single photon and biphotonic excitation considerably red-shifted in the matrices. The A(0_u⁺) → X(0_g⁺) emission of Se₂, not observed in the vapor, appears in the matrices with its origin near 15 100 cm^?1. Another system with ν₀₀ = 24 429 cm^?1 and ω″_e = 538 cm^?1 is thought to belong most probably to some polyatomic Se_n molecule.     

Two-exciton transition in the antiferromagnetic KNiF3 and K2NiF4

For the sharp band located at 31,200 cm^?1 in the three dimensional antiferromagnetic KNiF₃, the dependence of the oscillator strength on the Ni ion concentration and the stress-induced linear dichroic spectrum are studied. The polarization dependence of the corresponding band in the two dimensional antiferromagnetic K₂NiF₄ is also measured. The weak structure located at 30,780 cm^?1 is assigned as two-exciton transition, and the band at 31,200 cm^t?1 as a two-exciton transition accompanied with a T_1u phonon.     

不同波长激光激发下C6H12受激拉曼散射模式竞争

发现不同波长激光激发下C₆H₁₂的受激拉曼散射模式竞争现象. 在不同波长的激光激发下，不同拉曼模式的Stokes光占优势. 短波长(404，532nm)激光激发时小频移模式ω₁(802cm^-1)为弱增益模式，大频移模式ω₂(2852—3038cm^-1)为强增益模， 主要产生ω₂模式的Stokes光. 长波长(80 关键词： 模式竞争 6H₁₂')" href="#">C₆H₁₂ 受激拉曼散射     

On the mixed nature of the 740 cm band in wurtzite GaN films: A polarized Raman scattering investigation

A detailed study of the polarized Raman scattering of wurtzite GaN films is presented, focusing on the nature of the band centered at 740 cm⁻¹ observed in the X(Z, Z)X configuration. The origin of this band is ascribed to the mixed contribution of the A₁ and E₁ longitudinal phonon modes coupled with the free carrier excitation. The spectral profile of the 740 cm⁻¹ Raman band has been successfully reconstructed through a linear combination of the A₁-E₁ longitudinal phonon plasmon-coupled modes, leading to a free carrier concentration in good agreement with Hall effect measurements.     

Laser photoluminescence spectra of the M+S2− species in solid argon at 12K

Matrix reactions of alkali metal atoms with S₂Cl₂ and photolyzed H₂S samples have been examined by laser excitation at 457.9 nm. The strong photoluminescence spectrum from 12 300 to 18 300 cm^?1 exhibited vibrational spacings near 550 cm^?1. Observation of the same ZPL spectrum with two different precursors identified the carrier as Na⁺S₂^?. The vibrational numbering was made possible by the Na⁺³²S³⁴S^? species in natural abundance and from a 33% ³⁴S-enriched sample of S₂Cl₂. The spectroscopic constants ν₀₀ = 19 990 ± 10 cm^?, ω₀″ = 586 ± 2 cm^?1 and ω₀x₀″ = 2.8 ± 0.2 cm^?1 are in excellent agreement with those reported for S₂^? in alkali halide crystals at low temperature.     

Single crystal polarized Raman spectra of the solid electrolyte Cu2HgI4; attempt frequencies for ion motion in Ag2HgI4

The polarized Raman scattering from small single crystals of Cu₂HgI₄ provided assignments for the more prominent Raman features to specific irreducible representations. The E symmetry assignment, mass dependence, and pressure dependence of the 36 cm^?1 band in Cu₂HgI₄ and 24 cm^?1 band in Ag₂HgI₄ indicate that these features approximate the attempt frequency for ion hopping. The unusually high pre-exponential factor in the Arrhenius expression for ion hopping is discussed in light of the observed attempt frequency; we conclude that despite the high activation energy the conduction mechanism is similar to other heavy-metal solid electrolytes.