Exciton and phonon spectra of acoustooptic Tl3AsS3 crystals

The λ-modulated exciton reflection spectra of Tl₃AsS₃ crystals are investigated at 8 and 77 K, in which the ground (n=1) and excited (n=2, 3) exciton states are revealed. Taking into account the spatial dispersion, the shapes of λ-modulated reflection spectra of the n=1 line are calculated and the basic parameters of excitons and bands are determined (the translational and reduced masses of excitons and the effective masses of electrons and light and heavy holes). The one-phonon reflection spectra are studied in the region from 50 to 500 cm^?1 in polarizations E ∥ c and E ⊥ c. The shapes of one-phonon reflection spectra are calculated and the parameters of vibrational modes E and A ₂ are determined.     

The microwave spectra of symmetric top polyacetylenes: 1,3,5-Heptatriyne,CH3(CC)3H and 1-cyano-2,4-pentadiyne,CH3(CC)2CN

The rotational spectra of 1,3,5-heptatriyne, CH₃(CC)₃H and 1-cyano-2,4-pentadiyne, CH₃(CC)₂CN have been studied in detail between 26.5 and 40.0 GHz. The molecules have long linear chains of heavy atoms and show characteristic C_3v symmetric top spectra consisting of groups of R-branch lines at regular intervals separated by approximately 2B₀. Six isotopic modifications of CH₃(CC)₂CN have been detected in natural abundance allowing r_s substitution structural data to be derived for this species. Long linear polyacetylenic chains are quite flexible and this dynamic property manifests itself in the appearance of extended sequences of complex vibrational satellites associated with the bending of the chain. The vibrational ground state spectra as well as several low frequency vibrational satellites have been analyzed yielding various vibration-rotation parameters. For CH₃(CC)₃H B₀ = 778.2445 ± 0.0007 and for CH₃(CC)₂CN B₀ = 778.040 ± 0.001 MHz.     

Far infrared optical properties of proustite (Ag3AsS3)

The infrared reflection and transmission spectra of Ag₃AsS₃ single crystals have been between 20 and 650 cm^-1 at room temperature. Fourteen phonon modes were observable in reflectivity with the dominant restrahlen bands occuring at 360 cm^-1 and 35 cm^-1 for E? c and at 335 cm^-1 and 35 cm^-1 for E⊥ c. These measurements indicate that generation of far infrared radiation by mixing of two laser frequencies using proustite as the down-conversion crystal is not possible.     

Crystal structure and photoluminescence of (Y1−xCex)2Si3O3N4

Oxonitridosilicate phosphors with compositions of (Y_1−xCe_x)₂Si₃O₃N₄ (x=0−0.2) have been synthesized by solid state reaction method. The structures and photoluminescence properties have been investigated. Ce³⁺ ions have substituted for Y³⁺ ions in the lattice. The emission and excitation spectra of these phosphors show the characteristic photoluminescence spectra of Ce³⁺ ions. Based on the analyses of the diffuse reflection spectra and the PL spectra, a systematic energy diagram of Ce³⁺ ion in the forbidden band of sample with x=0.02 is given. The best doping Ce content in these phosphors is ∼2 mol%. The quenching temperature is ∼405 K for the 2 mol% Ce content sample. The luminescence decay properties were investigated. The primary studies indicate that these phosphors are potential candidates for application in three-phosphor-converted white LEDs.     

Vibrational spectra of M3PCr4O16 (M = K,NH4)

The infrared and Raman spectra of the two phosphochromates M₃PCr₄O₁₆ (M = K, NH₄) have been recorded and analysed. The spectra could be interpreted on the basis of the vibrations of Cr-O-P, O-P-O and CrO₃ groups. A large number of vibrational bands have been observed for each mode due to the existence of different Cr-O bond lengths. The anion is more distorted in potassium phosphochromate. The three ammonium groups are distinct.     

Lattice dynamics of MF3 crystals (M = Al, Ga, and In)

The phonon spectra, Born effective charges, and dielectric constants ε_∞ for the □AlF₃, □GaF₃, and □InF₃ crystals (where □ is a vacancy) have been calculated in terms of the generalized Gordon-Kim method. The calculated spectra of lattice vibrations contain no imaginary vibrational frequencies. This suggests the stability of the cubic phase of these compounds but contradicts the observable structural transition from cubic to rhombohedral phase. It is assumed that such a transition in the □AlF₃, □GaF₃, and □InF₃ crystals is brought about by structural defects. The calculated spectrum of lattice vibrations of the “completely defective” crystal M□F₃ (M = Al, Ga, and In) indicates a strong instability of the cubic phase. Within the mean crystal approximation, the cubic phase of M _x M _1?x F₃ crystals appears to be unstable at small x≤0.05.     

Coupled mode behavior of the soft E(TO) phonon of Pb(Ti1-x,Zrx)O3 and (Pb1-3x2, Lax)TiO3

We report the temperature dependence of the low frequency part (ω < 100 cm^?1) of the Raman spectra of the Pb(Ti_1-x, Zr_x)O₃ and $\text{(}\text{Pb}{}_{\mathrm{<mtext>1-</mtext><mtext>3x</mtext><mtext>2</mtext>}}$, La_x)TiO₃ systems. The spectra indicate a coupled mode behavior between the soft E(TO) phonon and a mode which produces an additional band in the spectra. We discuss the possibility that the additional band might be due to zone boundary tranverse acoustical phonons which couple to the q ～ 0 soft E(TO) mode because of the disorder existing in the systems.     

Spectroscopic investigation of rare-earth chromium borates RCr3(BO3)4 (R = Nd, Sm)

The optical absorption spectra of single crystals of neodymium and samarium chromium borates are studied. A magnetic phase transition in NdCr₃(BO₃)₄ (at T _c = 8 ± 1 K) and SmCr₃(BO₃)₄ (at T _c = 5 ± 1 K) is observed. The effective magnetic field acting on the Nd³⁺ ion from the side of the ordered magnetic subsystem of chromium is estimated.     

Vibrational spectra and elastic,piezoelectric, and magnetoelectric properties of HoFe3(BO3)4 and HoAl3(BO3)4 crystals

Raman spectra of light are obtained for HoFe₃(BO₃)₄ and HoAl₃(BO₃)₄ crystals at various temperatures and are used for determining the frequencies of crystal lattice vibrations at the center of the Brillouin zone. It is also found that the HoFe₃(BO₃)₄ crystal exhibits a phase transition at T _c ≈ 366 K. The magnetoelectric effect in the paramagnetic phase of these compounds is studied experimentally. The lattice vibration frequencies, elastic and piezoelectric moduli, Born dynamic charges, and the high-frequency permittivity are calculated using the density functional method. A peculiar behavior of the transverse acoustic vibration branch is observed in the Γ → Z direction of the Brillouin zone of the HoFe₃(BO₃)₄ crystal. The electric polarization induced by an external field is estimated using the calculated values of piezoelectric moduli and experimental values of magnetostriction.     

Spectroscopy of phonon and vibronic states of YbAl3(BO3)4 single crystal

The polarized Raman and reflection spectra of a single crystal YbAl₃(BO₃)₄ at room temperature were studied. Raman active vibrational modes A ₁, E _TO, and E _LO are identified. In the Raman spectrum, we detected an intense line at a frequency of 1018 cm⁻¹, which refers to internal vibrations of the BO₃ group and is known to be promising for use in amplifiers based on stimulated Raman scattering. From the simulation of reflection spectra by the method of dispersion analysis the frequencies of A ₂ vibrational modes were determined. Intense bands observed in the low-temperature transmission spectra in the range of f-f transitions in the Yb³⁺ ion are attributed to electron-phonon transitions. The Raman lines are compared with electron-phonon lines in the transmission spectrum.     

红色LiMBO3 : Re3+(Re=Eu,Sm) 发光材料的特性

采用固相法制备了红色LiM(M=Ca, Sr, Ba)BO₃ : Re³⁺(Re=Eu, Sm)发光材料,研究了材料的发光性能。研究发现LiM(M=Ca, Sr, Ba)BO₃ : Eu³⁺材料呈现多峰发射,最强发射分别位于610,615,613 nm处,分别监测这三个最强峰,所得激发光谱峰值位于369,400,470 nm。LiM(M=Ca, Sr, Ba)BO₃ : Sm³⁺材料也呈多峰发射,分别对应Sm³⁺的⁴G_5/2→⁶H_5/2、⁴G_5/2→⁶H_7/2和⁴G_5/2→⁶H_9/2跃迁发射;分别监测602,599,597 nm三个最强发射峰,所得激发光谱峰值位于374,405 nm。研究了激活剂浓度对材料发射强度的影响,结果随激活剂浓度的增大,发射强度先增强后减弱,即,存在浓度猝灭效应。实验表明,加入电荷补偿剂Li⁺、Na⁺或K⁺均可提高LiM(M=Ca, Sr, Ba)BO₃ : Re³⁺(Re=Eu, Sm)材料的发射强度。     

Optical phonon spectra of lutetium fluoride,oxyfluoride, and lutetium oxide nanoparticles

Nano-and microcrystalline LuF₃ phases have been synthesized with particle sizes of 30 nm and 30 μm, respectively. Analysis of the IR reflection spectra measured at T = 300 K showed that the nanophase differs from the microcrystalline phase by reduced optical phonon frequencies. It is established that annealing of the LuF₃ nanophase in air leads to the formation of nanoparticles of the LuO_{1 ? x} F_{1 + 2x} and Lu₂O₃ compositions. The IR reflection spectra of the nanophases indicate that these nanoparticles consist of an oxyfluoride core surrounded with a Lu₂O₃ shell; the latter is in the strained state.     

Spectral behavior study of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone

The photophysical properties such as singlet absorption, molar absorptivity, fluorescence spectra, fluorescence quantum yield (?_f) and transition dipole moment (μ₁₂) of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone (DMAPAPP) have been studied in different media. DMAPAPP exhibits a large red-shift in both absorption and emission spectra as the solvent polarity increases, indicating a large change in dipole moment of molecule upon excitation. The fluorescence quantum yield depends on the nature of the solvent. The absorption and emission spectra of DMAPAPP in dioxane–water mixture are also studied. The effect of different type of surfactants to determine their critical micellar concentration (CMC) and the microemulsion effect on the electronic absorption and emission spectra of DMAPAPP are recorded. The effect of acidity on the electronic absorption and emission spectra of DMAPAPP is studied to determine the pK_a and pK_a^? values.     

Raman studies of (Fe,V)3S4 solid solution

Raman scattering of Fe_xV_3-xS₄ with 0?x?2 has been studied. The observed spectra of V₃S₄, one of the end members of this solid solution, have been assigned to the Raman active lattice modes based on the C_2h³ space group symmetry. On the basis of the results obtained for V₃S₄, the nature of the metal-metal interactions and the site distributions of Fe atoms in (Fe, V)₃S₄ have been discussed.     

Microwave spectrum of chlorine nitrate (ClNO3)

Microwave spectra of chlorine nitrate (³⁵ClNO₃ and ³⁷ClNO₃) in the ground and first excited vibrational states have been analyzed in detail. Rotational constants and centrifugal distortion parameters are reported for each species. The permanent electric dipole moment in ClNO₃ was found to have two components, μ_a = 0.72 ± 0.07 D and μ_b = 0.28 ± 0.02 D.     

IR spectroscopy of rare-earth aluminum borates RAl3(BO3)4 (R = Y,Pr-Yb)

Rare-earth aluminum borates RAl₃(BO₃)₄ (R = Y, Nd-Yb) obtained by spontaneous high-temperature flux crystallization form two polytype modifications described by the space groups R32 (D ₃ ⁷ ) and C2/c (C _2h ⁶ ). They differ in the symmetry versions in mutual arrangement of layers. These borates have been investigated by mid- and far-IR spectroscopy in combination with factor-group analysis of the vibrations of BO ₃ ^3? ions; translational motions of Al³⁺, R³⁺ (Y, Nd-Yb), and BO ₃ ^3? ions; and BO ₃ ^3? rotations. Rare-earth aluminum borates are assigned to different space groups according to their IR spectra. Borates with large rare-earth Nd and Pr cations are crystallized into the space group C2/c (C _2h ⁶ ), while borates with smaller (Y, Sm-Yb) ions are crystallized into the space group R32 (D ₃ ⁷ ). The rhombohedral structure of the latter compounds includes monoclinically ordered domains, as is evidenced by the presence of monoclinic-phase bands in the IR spectrum. NdAl₃(BO₃)₄ and SmAl₃(BO₃)₄ can form both monoclinic and rhombohedral polytypes. The IR spectrum of the monoclinic SmAl₃(BO₃)₄ phase contains bands due to the rhombohedral phase, while the IR spectrum of NdAl₃(BO₃)₄ (which is described by the space group R32) contains bands due to the monoclinic polytype. The presence of domains with another arrangement of layers in the polytype structure is a characteristic sign that corresponds to the order-disorder theory; this theory explains the structure of polytypes.     

Far infrared optical properties of high Tc superconductors LnBa2Cu3Ox (Ln=Y, Ho, Er, Sm, GD, Dy, Eu, Pr)

Systematic measurements of the far infrared reflection spectra of high T_c superconductors LnBa₂Cu₃O_x for various Ln as shown in the title were performed. Infrared reflection spectra of tetragonal LnBa₂Cu₃O_x exhibit Reststrahlen vibration near 640, 590, 530, 355 and 250 cm^–1, common to these materials, and the spectra of the orthorhombic LnBa₂Cu₃O_x exhibit the characteristics of free carriers except PrBa₂Cu₃O_x with weak phonon structures near 617, 570, 317 and 285 cm^–1. PrBa₂Cu₃O_x is not a superconductor, and it has no characteristic broad band due to free carriers for all x in the range of 6 to 7. Lattice dynamical calculation was performed by the use of the shell model and the calculated results express quite well the characteristic features of infrared experiments.     

NMR in Li2 M 3Al(MoO4)4 triple molybdates (M = Rb,Cs)

Nuclear magnetic resonance (magic angle spinning) spectra of ⁷Li, ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei are measured in Li₂ M ₃Al(MoO₄)₄ triple molybdates (M = Rb, Cs) for the first time. Analysis of the nuclear magnetic resonance spectra reveal considerable asymmetry in the distribution of the electric charge throughout the crystal lattices of the compounds.     

CW laser action in acentric NdAl3(BO3)4 and KNdP4O12

We report low-threshold, room-temperature, cw lasing in two new high-Nd-concentration materials, NdAl₃(BO₃)₄ and KNdP₄O₁₂, the first ones with acentric space groups. For both materials, thresholds below 1 mW and slope power conversion efficiencies exceeding 20% have been measured. Fluorescence spectra and lifetimes have been measured in Nd_xGd_1?xAl₃(BO₃)₄ and Nd_xGd_1?xP₄O₁₂.     

Vibrational spectra of (CD3)2Cd and (CD3)2Zn

The Raman and infrared spectra of (CH₃)₂Cd and (CH₃)₂Zn have been reexamined and are reported along with previously unreported vibrational data for (CD₃)₂Cd and (CD₃)₃Zn. The spectra have been analyzed using the double group $\text{G}{}_{36}\text{2}$, which has led to some changes in assignments made previously. Comparison is also made with a recent study of (CH₃)₂Hg and (CD₃)₂Hg. Fine structure was observed for two of the vibrations of the E_1d symmetry species, arising from internal rotation of the methyl groups. This structure has been analyzed using a recently developed theory for molecules of the freely rotating dimethylacetylene type. Problems which arise in the application of this theory have been pointed out, and it is suggested that some additional consideration of the theory may be necessary.