Photoluminescence of chromium doped CdIn2S4

Well-resolved photoluminescence spectra of CdIn₂S₄: Cr³⁺ recorded at 77K and 2K have been analysed. The R-lines from the doublet ²E-⁴A₂ transition and their associated vibronic spectra have been assigned. These results yield a revised value for the crystal field parameter of B = 618 cm^-1     

I.R. reflection and transmission properties of KH2PO4

The i.r. a-axis reflection spectrum of KDP at 125K has been examined in the range 360-60 cm^?1, and the a — and c-axis reflection spectra have been measured at 290K in the range 700-10 cm^?1. The real and imaginary parts of the dielectric constants (?′ and ?″) have been obtained from the reflectivity measurements by Kramers-Kronig analyses. The low-frequency values of ?′ at 290K agree well with microwave values. The transmission spectra of thin KDP films at 290,125 and 110K have been examined and are found to be closely correlated with the ?″ spectra. We conclude that the films behave as if they contain crystallites of large surface area. A tentative identification of the lowest-frequency c-axis polar mode has been made in the 125K transmission spectrum.     

Optical spectra of CsI,CsBr, ZuGeP2, and SbSI

We report here the study of the normal reflectivity spectra R and the corresponding derivative spectra (1/R) dR/dE of SbSI between 2 and 6 eV. The spectra show very strong anisotropy. We have also tried to use the change of the wavelength modulation spectrum to monitor the change in the band structure of SbSI due to the phase transition at 292 °C (D_2h¹⁶→C_2v⁹). Careful examination of the spectra at various temperatures around T_c shows no observable change. We report also the wavelength-modulated reflectivity spectra of the chalcopyrite crystal ZnGeP₂ at 5 K between 2 and 6 eV, for E∥ C and E⊥ C. The experimental results are compared with the theoretical band structure calculation by de Alvarez and Cohen. We also present measurements on CsBr, CsI in the vacuum uv (between 5 and 8 eV) at 1.8K, showing noticeable difference with previous reflectivity measurements at 77 K.     

Electron spin relaxation studies of La@C82 in the solid state by EPR

The temperature dependence of EPR spectrum of La@C₈₂ in the powder of empty C₆₀ and C₇₀ mixed crystals was studied by EPR spectroscopy employing X- and Q-band microwave frequencies. The rigid limit spectra (at 4.2 K for the X-band and at 132 K for the Q-band) could be analyzed by static spectral simulation which yielded the EPR parameters,g _‖=2.0021,g _⊥=1.9970,^La A _⊥=7.8 MHz,^La A _‖～0 MHz and an isotropic¹³C coupling value of about 3 MHz. For higher temperatures an appreciable motional averaging effect was observed and the spectra were analyzed by using dynamic spectral simulation based on the stochastic Liouville equation, where we assumed an isotropic rotational motion with the Brownian diffusion. The calculated spectra reproduced the dominant feature of the temperature dependence of the spectra almost satisfactorily for both the X-and Q-band frequencies with the appropriate rotational correlation times. The Arrhenius plots of the correlation time gave two activation energies of 0.9 kcal/mol and 2.9–3.8 kcal/mol for the temperatures below and above 200 K, respectively.     

Infrared absorption in In-doped degenerate Hg1−xCdxTe

The infrared absorption spectra, including absorption edge spectra and below-gap absorption spectra, were investigated both experimentally and theoretically for an In-doped degenerate HgCdTe sample with an electron concentration N_e = 7.0 × 10¹⁷ cm^-3 for wavelengths 7 μm<L<17 μm at the temperatures 77 K <T< 300 K. The possibility of applying free-carrier absorption theory developed for InSb to HgCdTe is discussed. It is concluded that the virtual crystal approximation works fairly well for HgCdTe and that the two-mode Callen effective charge should be used in the calculation of free-carrier absorption coefficients to account for the two-mode character of the optical phonons of HgCdTe. Good agreement between theory and experiment in the below-gap absorption spectra was obtained. The concentration of ionized impurities was found to be N_imp=3.4 × 10¹⁸ cm^-3. A good account of the behaviour of absorption edge in the light of Burstein-Moss effect has also been given.     

Far infrared polarization measurements of MEM(TCNQ)2 at room temperature and 4.2 K

Polarization measurements have been made in the far infrared absorption spectra on single crystals of MEM(TCNQ)₂ at 1.5, 4.2 and 298 K. We demonstrated experimentally that the direction of polarization of phonons at 126 and 156 cm⁻¹ below spin-Peierls transition are parallel to the c-axis. Secondly, we measured the absorption spectra of MEMI powder at 1.5 and 4.2 K and found that there is no absorption in the range from 130 to 170 cm⁻¹. This indicates that there is no intramolecular vibration of MEM in this region. It supports the assignment of 156 cm⁻¹ absorption as phonon. Thirdly, comparing the FIR absorption spectra at 4.2 and 298 K with linearly polarized radiation field parallel to the c-axis, we found that the height of the strong absorption band observed around 86–180 cm⁻¹ region at 4.2 K becomes lower with the raising of temperature to 298 K. We attributed this band to the pinned CDW. The lowest edge of the CDW is 70 cm⁻¹.     

Protein dynamics in57Co doped concanavalin A

Mössbauer emission spectra of⁵⁷Co in solutions of the saccharide binding protein concanavalin A have been obtained between 90 K and 238 K. The spectra were analyzed taking into account after-decay effects and between 200 and 238 K, using the bound diffusion model. The mean square amplitude, ?x ²?, of the collective motion was found to be smaller in concanavalin A with saccharide, than in that without it.     

Luminescence of Tl<Superscript>+</Superscript> ions in a KZnF<Subscript>3</Subscript> crystal

The luminescence spectra of a KZnF₃: Tl⁺ crystal are investigated in the energy range from 4.75 to 5.9 eV at temperatures of 10–300 K upon excitation into the A absorption band (5.7–6.3 eV). At T=300 K, the luminescence spectra exhibit an intense band with a maximum at 5.45 eV, which is attributed to single Tl⁺ ions substituted for K⁺ ions. The 5.723-eV intense narrow band observed at T<20 K is assigned to the ³Γ_1u-¹Γ_1g zero-phonon transition, which is weakly allowed by the hyperfine interaction. The luminescence decay is studied as a function of temperature. The main characteristics of the luminescence spectra are adequately described in terms of the semiclassical theory based on the Franck-Condon principle and the Jahn-Teller effect for an excited sp configuration of the Tl⁺ ion with the use of the parameters obtained earlier from analyzing the absorption spectra of the system under investigation.     

Mössbauer spectra of 57Fe in MnAs

Mössbauer spectra of 0.25 at% ⁵⁷Fe in ferromagnetic MnAs were observed for 70 K ? T ? 420 K. We infer a magnetostrictive coupling of the low spin interstitial Fe⁺² atoms and find evidence for a local soft phonon mode.     

Transitions in41K studied with the (n,n′γ) reaction

Singles gamma ray spectra of the⁴¹K(n, n′γ)⁴¹K reaction have been measured with fast reactor neutrons. The populated states and γ-ray intensities are compared with those of the⁴⁰K(n, γ)⁴¹K reaction. About 91% of the observed gamma ray intensity was assigned to the decay of 35 states in⁴¹K. The energy and spin dependence of the gamma ray fluxes in both reactions are discussed.     

Local and dynamic Jahn-Teller distortion in ulvöspinel Fe2TiO4

⁵⁷Fe Mössbauer spectroscopic study on ulvöspinel Fe₂TiO₄ has been conducted in a wide temperature range from 16 K to 500 K. The paramagnetic spectra are composed of several high spin Fe^2?+? doublets even at 500 K, which is rather strange because the point symmetry of the A-site is completely cubic (??43m). We explain the electric field gradient (EFG) at A-site by the local arrangement of Fe^2?+? and Ti^4?+? on the B-site. The spectra were successfully analyzed by four-subspectra model, which is based on the B-site arrangement. The model also fits rather well to the magnetically ordered spectra. Thus the temperature variations of the hyperfine parameters were obtained. The Néel temperature (T _N) is estimated to be about 125 K. The quadrupole coupling constants e ² qQ/2 of A-site subspectra show little change around cubic-tetragonal transition temperature (T _t?=?163 K), but rapidly increase below T _N. From the temperature variation of line width, we found local and dynamic Jahn-Teller distortions around A-site Fe^2?+? ions in the cubic phase.     

ESR and photoacoustic spectra of V2O5−MO2 (M = Se, Te, Ge) glasses

ESR spectra of V₂O₅?MO₂ (M = Ge, Se, Te) glasses are investigated in the range 298–498 K. The spectra at 298 K are characteristic of V⁴⁺ with the 3d¹ electron localized on a single ${}^{51}\text{V}\text{(I =}\text{7}\text{2}$) in the glass network. At higher temperature, the hyperfine structure progressively broadens, leading eventually to a broad, single ESR peak. These results are consistent with thermally-induced electron hopping from V⁴⁺ to V⁵⁺. Photoacoustic spectra of the glass at 298 K are characteristic of V⁴⁺ in a distorted octa environment. A correlation of ESR and PAS data suggests that covalency increased as M is charged from Ge through Te to Se.     

The transition from dynamics to statics in the electron-spin-resonance spectra of impurity Mn2+ ions in strontium titanate

The electron-spin-resonance (ESR) spectra of SrTiO₃:Mn single crystals have been investigated. Results unambiguously indicate that the impurity center formed by an Mn²⁺ ion has a dynamic nature. In the high temperature range (T > 100 K), ESR spectra of Mn²⁺ ions reveal cubic symmetry; the spectrum is found to broaden significantly with a decrease in temperature. Upon cooling to T < 10 K, low-symmetry centers of Mn²⁺ ions with a strong orientational dependence emerge in the spectra. Temperature evolution of the ESR spectrum can be described within the model of a dynamic off-center Mn²⁺ ion substituting for the Sr²⁺ ion, with a transition to the static regime at low temperatures with an average localization energy of ～2.4 ± 0.4 meV for Mn²⁺ centers due to random deformations.     

Multiple trapping sites for potassium atoms in argon matrices

Argon crystals were dopes with 0.2 ppm of ⁴¹K through the nuclear reaction ⁴⁰Ar(n, β^-)⁴¹K. The X-band electron spin resonance spectrum of ⁴¹K was observed. The recorded spectra clearly show the existence of different trapping sites for potassium in argon. Zero-field hyperfine splittings and g-values of potassium on these sites are determined.     

Low temperature Raman study on the site symmetry of ZnSe:P

Raman spectra of phosphorous doped ZnSe are recorded from 9 to 300 K. In addition to TO mode at 208 cm⁻¹ and LO mode at 253 cm⁻¹, a new mode around 240 cm⁻¹ is observed between 55 and 270 K. The spectra at lower and higher temperatures do not show the new mode. This new mode confirms that there is a reduction of (Se site) symmetry from T_d to C_3v when P substitutes for Se. This is due to Jahn Teller distortion.     

Comparison of band model and integrated line-by-line synthetic spectra for methane in the 2.3 μm region

The 2.3 μm spectral region of methane can be used to retrieve cloud properties of planetary spectra, provided parameters for the methane spectrum are known. Two standard techniques for calculating absorption spectra in this region are compared here. A Voigt profile Mayer-Goody random band model is applied, using coefficients empirically fitted by Fink et al. to CH₄ spectra recorded with high absorping amounts at 10 cm^?1 resolution. Calculation of the absorption is also done with a line-by-line direct integration method for the same gas conditions using molecular parameters obtained by combining an older unpublished list of observed positions and estimated line strengths (derived from 0.04 cm^?1 resolution data) with quantum assignments from the literature. The molecular parameters have been evaluated for the 4180–4590 cm^?1 region by comparing new laboratory spectra with 0.01 cm^?1 resolution recorded at 296 and 153K with synthetic spectra calculated at the same conditions. The deficiencies of the molecular parameters and random band coefficients for this spectral region of CH₄ are then discussed qualitatively and demonstrated by comparing 10 cm^?1 resolution synthetic spectra calculated by both methods for the same gas conditions at 296, 153, and 55 K.Curves of growth of the total equivalent width are calculated at 296 and 55K for a pathlength of 50 cm and pressures up to 10 atm. Changing the mean line spacing in the band model gives better agreement between the spectra calculated by the two techniques at low gas temperatures. The required multiplier has been determined for the mean line spacing for pressures from 10^?6 to 10^?1 atm at 55, 100, and 150 K.     

Magnetism of ErAgSn studied by 119Sn Mössbauer spectroscopy

Antiferromagnetic ErAgSn compound was investigated in detail by ¹¹⁹Sn Mössbauer spectroscopy in a temperature range between 2.2 and 300 K. The ¹¹⁹Sn spectra recorded below 4.2 K can be well fitted with a single main magnetic component in agreement with recent neutron diffraction studies [1]. A broad distribution of magnetic hyperfine fields observed above 4.2 K and enhanced spin correlations among Er³⁺ ions at T > T _N = 5.6 K are the remarkable features of the investigated system.     

Central peak in the strontium titanate crystal near the tetragonal-to-cubic phase transition

Raman spectra of the SrTiO3 crystal have been measured in wide temperature (22?C316 K) and frequency (2?C1020 cm^?1) ranges. It has been shown that a central peak appears in low-frequency Raman spectra at temperatures above 70 K. In the spectral geometry with polarization rotation near the temperature T _c = 106 K of the cubic-to-tetragonal phase transition, the central peak exhibits properties of the order-disorder phase transition. Such a behavior of the central peak has been explained by the interaction of the low-frequency soft mode E _g with the relaxation mode near T _c .     

Level structure of the 89-neutron nucleus 153Gd: (I). Levels and gamma-transitions in 153Gd excited in the decay of 153Tb

Investigations of the properties of ¹⁵³Gd excited states populated in ¹⁵³Tb decay were continued. The following measurements were performed: coincidence spectra e^?γ with L41, K93 + L52, K110, K129 + L87 + L88 and K195 + L152 keV conversion electron lines, angular correlations of high energy γ-cascades going through the 109.7 keV level, delayed e^?γ and e^?e^? coincidence spectra to determine the half-lives of 41.5, 93.3, 109.7, 129.1,183.5, 212.0 and 216.1 keV states, R(135°, ± B) parameters of IPAC for the 102–110 and 83–129 keV cascades using ¹⁵³Tb sources implanted into Fe foil.A decay scheme of ¹⁵³Tb containing 50 excited levels is proposed. Their spins, parities, $\text{log}\text{?t}$ and, for low-lying levels, also the mean half-lives have been determined. An estimation of the g-factors of the 109.7 and 129.1 keV levels has been given. On the basis of half-lives of investigated states absolute values of reduced γ-transition probabilities for these states have been calculated. The structure of the ground state of ¹⁵³Gd is discussed.     

Variable temperature EPR spectra of Copper (II) ions in kainite crystals

X-band electron paramagnetic resonance (EPR) studies on divalent copper ions embedded in KMgClSO₄·3H₂O single crystals have been performed at low temperature (123 K). The angular variation of the EPR spectra reveals the presence of two Cu²⁺ sites, which have different orientations. The spin-Hamiltonian parameters of this six-coordinated cupric ion have been evaluated from the EPR spectra at 123 K. The forbidden lines due to Δm_I=±1 transitions are observed in between allowed transitions. The temperature variation EPR studies have also been performed both for a single crystal and a polycrystalline sample. The ground state wavefunction of Cu²⁺ ions has been estimated and is found to be an admixture of d_3z²−r² and d_x²−y². The temperature variation of the EPR spectra reveals that Cu²⁺ ions exhibit dynamic Jahn-Teller effect. From the polycrystalline EPR data, the temperature dependent magnetic susceptibilities are evaluated and discussed.