Multiphonon relaxations in crystalline uranyl salts

1979 ◽  
Vol 57 (11) ◽  
pp. 2045-2049 ◽  
Author(s):  
W. K. Chan ◽  
K. H. Chun ◽  
T. W. Lai ◽  
A. F. Leung
Keyword(s):  
Temperature Dependence ◽  
Decay Rate ◽  
Quantum Efficiency ◽  
Low Temperatures ◽  
Room Temperature ◽  
Fluorescence Decay ◽  
Multiphonon Relaxation ◽  
Electronic Level ◽  
Radiative Processes ◽  
Fluorescence Light

The fluorescence decay rate observed is associated mainly with the intramolecular relaxation of the excited uranyl ion despite the presence of impurities, defects, and self-absorption of fluorescence light in the crystal. Multiphonon transitions dominate the relaxation at temperatures higher than room temperature. The parameters of the multiphonon relaxation are extracted from the temperature dependence of fluorescence decay rate. The parameters show that at low temperatures the quantum efficiency of the fluorescent level is greater than 0.80 and that of the electronic level above the fluorescent level is less than 0.13. The absence of fluorescence from the electronic level above the fluorescent level is due to fast depopulation by non-radiative processes and low quantum efficiency.

Transport Properties of Granular Nix(SiO2)100−x Thin Films

1990 ◽  
Vol 195 ◽  
Author(s):  
John R. Beamish ◽  
B.M. Patterson ◽  
K.M. Unruh
Keyword(s):  
Thin Films ◽  
Temperature Dependence ◽  
Electrical Transport ◽  
Low Temperatures ◽  
Room Temperature ◽  
Volume Percent ◽  
Ni Content ◽  
Resistivity Minimum ◽  
Temperature Coefficient Of Resistivity ◽  
Sputter Deposited

ABSTRACTWe have studied the electrical transport behavior of sputter deposited Nix(SiO2)100−x thin films between room temperature and 100 mK and, at selected temperatures, in applied magnetic fields up to 6 T. As the Ni concentration x is reduced, the resistivity increases systematically. At a Ni concentration (nominal) of about x–70 atomic percent (38 volume percent) the room temperature coefficient of resistivity changes sign. For Ni concentrations greater than 70 percent the resistance first decreases with temperature then increases logarithmically at, low temperatures. This increase becomes smaller and the resistivity minimum moves to progressively lower temperatures as the Ni concentration increases. In films with less than x–70 percent Ni, the resistivity has a temperature dependence of the form ρ(T)–ρo exp \(To/T)α] between room temperature and about 5 K. The exponent a is about 1/2 and To increases with decreasing Ni content. Below 1 K, however, the resistivity increases much less rapidly, with a temperature dependence independent of Ni concentration. In all films the magnetoresistance is small and negative.

Anomaly of Nuclear Quadrupole Relaxation in Cu2O Prepared at Low Temperatures

1986 ◽  
Vol 41 (1-2) ◽  
pp. 382-385 ◽  
Author(s):  
J. Kasprzak ◽  
J. Lus ◽  
J. Pietrzak
Keyword(s):  
Temperature Dependence ◽  
Cuprous Oxide ◽  
Thermal Processing ◽  
Low Temperatures ◽  
Room Temperature ◽  
Quadrupole Relaxation ◽  
Temperature Dependences ◽  
Powder Samples ◽  
Nuclear Quadrupole ◽  
Nuclear Quadrupole Relaxation

The 63Cu and 65Cu NQR transitions in powder samples of cuprous oxide have been investigated from 77 to 500 K and at room temperature after annealing up to 1100 K Significant differences in T1 , NQR linewidth Δv, and their temperature dependences were found among the samples prepared in different ways. For C u20 samples obtained in low temperatures (below 380 K), the temperature dependence of T1 below 380 K is o f activation character with Ea = 0.07 eV. These results are interpreted in terms of an electron hopping mechanism. Thermal processing of these samples permits to obtain irreversible electronic state and then the spectroscopic parameters are the same as for the samples obtained in high temperatures (above 1320 K).

scholarly journals Temperature Dependence of the Bragg Peak-Intensity Close to the α-Incommensurate-β Transition in Quartz

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
Hamit Yurtseven ◽  
Koray Kaymazlar
Keyword(s):  
Phase Transition ◽  
Temperature Dependence ◽  
Atmospheric Pressure ◽  
Low Temperatures ◽  
Order Parameter ◽  
Room Temperature ◽  
Bragg Peak ◽  
Threefold Axis ◽  
First Order ◽  
Peak Intensity

Quartz as a mineral has a stable crystalline phase at room temperature and atmospheric pressure; at low temperatures it is in the α phase and when it is heated up, it transforms into the β phase through the intermediate (incommensurate) phase within the temperature interval of nearly 1.3 K at around 847 K. The order parameter Q occurs due to a tilting of SiO4 tetrahedra around the threefold axis, which can be related to variation of the peak-intensity with the temperature in quartz. In this study, we analyze the temperature dependence of the Bragg peak-intensity measured through the α-β transition in quartz, as obtained from the literature according to a power-law formula. From our analysis, we deduce the values of the critical exponent β for the order parameter (Bragg peak-intensity) for the α-incommensurate (IC-)β transition. Our β values indicate that the β-IC phase transition is of a second order and that the IC-α phase transition is of a weak first order, as also reported in the literature.

Temperature Dependence of Hydrogen Solubility and Diffusivity in Hydrogen Permeable Membrane of Pd-Cu Alloy with B2-Type Crystal Structure

2021 ◽  
Vol 407 ◽  
pp. 31-40
Author(s):  
Hiroshi Yukawa ◽  
Shimpei Watanabe ◽  
Asuka Suzuki ◽  
Yoshihisa Matsumoto ◽  
Hideki Araki ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Low Temperatures ◽  
Room Temperature ◽  
Hydrogen Diffusion ◽  
Hydrogen Permeation ◽  
Hydrogen Permeability ◽  
Hydrogen Flux ◽  
Cu Alloy ◽  
B2 Structure ◽  
Type Crystal

The temperature dependence of hydrogen solubility and diffusivity of Pd–53mol%Cu alloy membrane with the B2–type crystal structure has been investigated. The hydrogen permeation tests are performed using ultra–pure hydrogen (more than 9N) purified by a Pd–Ag alloy membrane to avoid any influences of impurities. It is found that the hydrogen permeability decreases significantly at low temperatures, especially near room temperature. The time dependence of hydrogen flux is monitored and found that the hydrogen flux decreases gradually during about 4 ~ 5 days after rapid cooling down to room temperature from 623 K.The results of the temperature dependence of the hydrogen permeability are analyzed in view of the consistent description of hydrogen permeation based on hydrogen chemical potential, where the hydrogen flux is proportional to the product of the mobility for hydrogen diffusion, B, and the PCT factor, fPCT. In this study, the pressure–composition–isotherms (PCT curves) for Pd–53Cu alloy with B2 structure are measured for the first time by the in–situ XRD–PCT method, and they are applied to estimate the PCT factors. Then, the temperature dependence of the PCT factor and the mobility for hydrogen diffusion is evaluated. It is revealed that the decrement in hydrogen permeability at low temperatures is mainly attributable to the decrement of the mobility for hydrogen diffusion.According to the positron annihilation experiments, the defects density is considered to be small in Pd–53Cu alloy with the B2 structure even at room temperature, suggesting that the excess Cu atoms in Pd–53Cu alloy occupy the positions of Pd sublattice, at which the Cu atoms form a local BCC–Cu unit. The diffusion of Cu atoms corresponds to the diffusion of BCC–Cu units in the B2 structure. Therefore the diffusion of Cu atoms and the configuration of BCC–Cu units in B2 structure could be a key to understand the gradual transition of hydrogen diffusivity at low temperatures.

Temperature Dependence of the Electrical Conductivity of Poly(Benzo[1,2-b:4,5-b'] Dithiophene-4,8-Diyl Vinylene) and Poly(Dodecylthiophene)

1997 ◽  
Vol 488 ◽  
Author(s):  
R. C Hyer ◽  
R. G. Pethe ◽  
T. Yogi ◽  
S. C. Sharma ◽  
J. Wang ◽  
...  
Keyword(s):  
Thin Films ◽  
Electrical Conductivity ◽  
Temperature Dependence ◽  
Low Temperatures ◽  
Room Temperature ◽  
Thermal Fluctuation ◽  
Variable Range Hopping ◽  
Tunneling Model ◽  
Three Samples ◽  
Electrical Conductivities

AbstractWe present results for the electrical conductivity (σ) of thin films of poly(benzo[1,2-b:4,5- b']dithiophene-4,8-diyl vinylene) (PBDV) and poly (dodecylthiophene) (PDDT) as a function of temperature in the range 15-295K. The polymers were doped with FeC13 and PF6 which resulted in electrical conductivities differing by two orders of magnitude at room temperature. We examine three sets of σ(T)-data by using the variable-range hopping (VRH) model that predicts a linear relationship between ln(T1/2σ) and T1/4. We observe a change in the slope of the ln(T1/2σ) vs T14 relationship in all three samples at low temperatures. We also analyze the temperature dependence of the resistivity of PBDV by using the thermal fluctuation-induced tunneling model.

Bestimmung der Röntgen-Debye-Temperatur aus dem Borrmann-Effekt in Germanium / Determination of the X-ray Debye Temperature in Germanium by Means of the Borrmann Effect

1973 ◽  
Vol 28 (7) ◽  
pp. 1204-1213 ◽  
Author(s):  
J. Ludewig
Keyword(s):  
Temperature Dependence ◽  
Compton Scattering ◽  
Debye Temperature ◽  
Low Temperatures ◽  
Room Temperature ◽  
Perfect Crystal ◽  
Photoelectric Absorption ◽  
Temperature Dependent ◽  
X Ray

The anomal transmission of CuK radiation through "thick"' perfect crystal slices of Germanium is strongly temperature dependent. This temperature dependence was measured between 293 and 6 K in the (220) symmetric Laue case and used to evaluate the Debye temperature θM . The wellknown uncorrected value θ′M = 290K was obtained near room temperature. Taking into account TDS and Compton scattering in addition to the photoelectric absorption the corrected value θM = 294 or 296 K was found, depending on the source of data. With decreasing temperature the corrected θM increases slightly up to a maximum at very low temperatures, as predicted by Batterman and Chipman and by Salter.

Einfluß der nematischen Ordnung auf die Fluoreszenz von Perylen und 4-Dimethyl-amino-4′-nitrostilben / Influence of the nematic order on the fluorescence of perylene and 4-dimethyl-amino-4’-nitrostilbene

1979 ◽  
Vol 34 (7) ◽  
pp. 799-803 ◽  
Author(s):  
Gunter Ullrich
Keyword(s):  
Energy Transfer ◽  
Binary System ◽  
Temperature Dependence ◽  
Quantum Efficiency ◽  
Fluorescence Decay ◽  
Total Absorption ◽  
Nematic Order ◽  
Temperature Range ◽  
Absorption Power

The temperature dependence of absorption, emission and fluorescence-decay in EBBA has been investigated. The total absorption power μ=μ∥+2·μ⊥ was found to be constant over the whole investigated temperature range. For perylene a decrease of the quantum-efficiency with growing temperature was observed, but not for 4-dimethyl-amino-4′-nitrostilbene (DMANS). In the binary system an energy transfer via dipol-dipol interaction was observed. In the ordered phase energy-transfer distances about 30 Å and less were computed.

Phase Transition and Crystal Dynamics of 4-Bromobenzyl Alcohol

1998 ◽  
Vol 53 (6-7) ◽  
pp. 436-441 ◽  
Author(s):  
Masao Hashimoto ◽  
Yuko Monobe ◽  
Hiromitsu Terao ◽  
Haruo Niki ◽  
Koichi Mano
Keyword(s):  
Phase Transition ◽  
Dielectric Constant ◽  
Phase I ◽  
Temperature Dependence ◽  
Low Temperatures ◽  
Room Temperature ◽  
Molecular Motion ◽  
Dielectric Dispersion ◽  
Compound A ◽  
Crystal Dynamics

Abstract For the title compound a phase transition from Phase II to Phase I (low and room temperature phases, respectively) was found at ca. 217 K. The temperature dependence of the 81Br NQR frequency and that of the dielectric constant showed anomalies at ca. 195 K that were tentatively attributed to a higher order phase transition. A similar anomaly was found at ca. 218 K for 4-chlorobenzyl alcohol which showed a II-I transition at 236 K. The dielectric dispersion observed for both compounds at low temperatures indicates an excitation of a molecular motion with the dielectric relaxation rate of ca. 1 kHz. The temperature dependence of the 81Br NQR frequencies of 2-and 3-bromobenzyl alcohol, measured at T > 77 K, gave no evidence of phase transition in their crystals.

Unusual Temperature Dependence of the Fluorescence Decay in Heterostructured Stilbene

2021 ◽  
Author(s):  
Renata Karpicz ◽  
Nina Ostapenko ◽  
Yura Ostapenko ◽  
Yaroslava Polupan ◽  
Igor Lazarev ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Wide Temperature Range ◽  
Fluorescence Spectra ◽  
Room Temperature ◽  
Fluorescence Decay ◽  
Decay Kinetics ◽  
Temperature Range ◽  
Fluorescence Decay Kinetics ◽  
Kinetics Of

Fluorescence spectra as well as fluorescence decay kinetics of hot-pressed and sublimated films of stilbene has been studied in wide temperature range, from 15 K up to room temperature. Fluorescence...

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