Observation of magnetic field dependent ultrasonic relaxation time in p-InSb

Ultrasonic attenuation and sound velocity measurements are presented for p-InSb (≈ 10¹⁴cm^?3) at low temperatures in high magnetic fields. A magnetic field dependent relaxation time is observed, which is interpreted as being due to a relaxation process via holes in the valence band.     

Nuclear magnetic resonance measurements and the energy band structure of PtSn

Nuclear magnetic resonance measurements of the Knight shift and spin-lattice relaxation time for ¹⁹⁵Pt and ¹¹⁹Sn in PtSn are reported. The energy band structure as determined by the relativistic orthogonalized plane wave method is also presented. The band model developed has holes in the Pt d-band but does not have a large density of states associated therewith.     

Theory of nuclear magnetic resonance line shapes for spin systems containing several quadrupolar nuclei

The general method of calculating the high resolution nuclear magnetic resonance band shape of a group of spin -½ nuclei scalar coupled to more than one quadrupolar nucleus is described, the ²A³X³Y case considered in detail, and computed spectra presented. The detailed treatment is carried out with the assumption that molecular reorientation is sufficiently rapid for the extreme narrowing approximation to be applicable. The relationship between the relaxation matrix method of conducting such band-shape calculations and that based upon analogy with chemical exchange is investigated and it is concluded that the latter approach is inadequate. The band shapes resulting in the limit of rapid quadrupole relaxation are discussed and it is shown that these can be understood using a theory [6] of scalar relaxation of the second kind.     

Femtosecond multicolor transient absorption spectroscopy of colloidal silver nanoparticles

Time-resolved femtosecond multicolor absorption spectroscopy of silver nanoparticle (NP) colloids with particle diameter in range of 10–30 nm is presented. The amplified femtosecond excitation of the surface plasmon resonance band resulted in transient absorption spectra reflecting the electron-phonon relaxation dynamics, which takes place on the early picosecond time scale. The monitored band with enhanced absorption in the 490–540 nm spectral range exhibited red-shift with increasing pump fluency from 0.4 mJ/cm² to the 1.5 mJ/cm² level. The growth of the relaxation time with increasing pump fluency reveals the temperature dependent relaxation dynamics caused by the nanometer sized electron confinement in the case of silver. This effect was confirmed also by identification of the relaxation time dependence on the particle diameter at constant pump fluency. The complex experimental results revealed nonlinearities both in the laser excitation and electron relaxation processes.     

Nuclear spin relaxation,hybridization, and low-temperature 4f spin fluctuations in intermediate-valent SmB6

¹¹B spin-lattice relaxation measurements have been carried out in SmB₆ samples with large low-temperature resistivities. Above 15 K the relaxation is activated, with approximately the same gap (≈6 meV) as found previously in transport and optical measurements. 4f spin fluctuations apparently dominate the relaxation, so that these results give strong evidence for 4f-conduction band hybridization at the gap edge. An anomalous peak in the relaxation rate was observed at ≈5 K, which is tentatively attributed to fluctuations of “remagnetized” Sm³⁺ ions near Sm-site vacancies.     

Nonradiative relaxation of photoexcited O<Stack><Subscript>1</Subscript><Superscript>0</Superscript></Stack> centers in glassy SiO<Subscript>2</Subscript>

The processes involved in the excited-state relaxation of hole O ₁ ⁰ centers at nonbridging oxygen atoms in glassy SiO₂ were studied using luminescence, optical absorption, and photoelectron emission spectroscopy. An additional nonradiative relaxation channel, in addition to the intracenter quenching of the 1.9-eV luminescence band, was established to become operative at temperatures above 370 K. This effect manifests itself in experiments as a negative deviation of the temperature-dependent luminescence intensity from the well-known Mott law and is identified as thermally activated external quenching with an energy barrier of 0.46 eV. Nonradiative transitions initiate, within the external quenching temperature interval, the migration of excitation energy, followed by the creation of free electrons. In the final stages, this relaxation process becomes manifest in the form of spectral sensitization of electron photoemission, which is excited in the hole O ₁ ⁰ -center absorption band.     

Shape of the IR bands of CH4: The CH4-Kr system in different phase states

The IR absorption spectrum of mixtures of CH₄ with Kr in the range 800–6000 cm^?1 is studied in the region of the gas-liquid and liquid-crystal phase transitions. It is found that, as the system density increases, the ratio of the ν₄ band intensity to that of the ν₃ band becomes larger and the measured values of the second spectral moment of the ν₄ band become smaller than the corresponding calculated values. The quantum counterpart of the generalized J-diffusion model was used to describe the shape of the ν₃ and ν₄ bands, and the rotational relaxation times of CH₄ in solutions were obtained. It was shown that, as the density increases, a broad 1470-cm^?1 band appears in the region of the “forbidden” (induced by a Coriolis interaction) ν₂ band (ν_Q=1535 cm^?1) detected in a low-density gas. The intensity of this band is appreciably higher than that of the ν₂ band.     

红宝石Cr3+离子的自旋-晶格弛豫时间和浓度效应

本文叙述用脉冲饱和法测量自旋-晶格弛豫时间的实验及其结果。在显示方面使用了倍频同步法以产生基线,便于读取T₁。测定了红宝石Cr³⁺离子的弛豫时间,肯定在77°K时各种跃迁的T₁大致相等,但浓度增高时T₁降低。     

Determination of Plasma Frequency and the Pulse Relaxation Time in Doped Semiconductors by FIR Surface Waves

The Surface Electromagnetic waves method was applied for determination of plasma frequency and pulse relaxation time in doped A³B⁵ semiconductors. The influence of plasmon phonon interaction, nonparabolity of the conduction band, electron scattering peculiarities, presence of disturbed layers are under consideration.     

Optically detected magnetic resonance of the zinc vacancy in ZnS

Optical detection of magnetic resonance (ODMR) is reported for the single negative charge state, V_Zn^?, of the isolated zinc vacancy in ZnS. Produced by 2.5 MeV electron irradiation, it is detected in a distant donor-acceptor (DA) pair luminescent band at 570 nm in which the vacancy acts as the acceptor. Excitation and emission spectral dependences of the V_Zn^? ODMR signals are analyzed in terms of a configurational coordinate model. We conclude that the double acceptor level (V_Zn⁼/V_Zn^?) is located ～1.1 eV from the valence band edge and that the trigonal Jahn-Teller relaxation energy for the V_Zn^? state is ～0.5 eV.     

Intense red upconversion luminescence from Tm³⁺/Yb³⁺ codoped transparent glass ceramic

Tm³⁺/Yb³⁺ codoped transparent glass ceramic containing β-PbF₂ nanocrystals was successfully prepared. After thermal treatment, emissions from the ¹G₄ state of Tm³⁺ excited by 980 nm laser were greatly quenched by cross relaxation and the 700 nm luminescence from Tm³⁺:³F_2,3→³H₆ transition was strongly enhanced. A nearly monochromatic red luminescence band was observed. Based on the luminescence decay curves and Judd-Ofelt analysis, the strengthened cross relaxation played an important role in such phenomenon.     

硅中空穴与核的超精细作用及p型硅的核磁弛豫

本文把半导体中载流子和它的原子核的超精细作用(包括非接触项)表达为作用在有效质量波函数上的“准接触作用”。具体对硅中Si²⁹核和价带空穴的这个作用可表达为{S₁(J_xμ_nx+J_yμ_ny+J_zμ_nz)+S₂(J_x³μ_nx+J_y³μ_ny+J_z³μ_nz)}δ(r-r_n),参量S₁、S₂是联系着价带顶的波函数的一些积分;一般地S₂≈0。用它来处理了p型硅中Si²⁹核的核自旋弛豫,得到弛豫时间的表达式;从弛豫时间的实验值估计了S₁的值;还从价带自旋轨道分裂值估计了同一参量。     

Temperature dependence of the hyperfine interactions of the β-emitter 12N in Ni

The temperature dependence of the magnetic hyperfine field and the nuclear spin-lattice relaxation time of ¹²N in Ni was determined in the region from 98 K to 773 K by use of NMR detection. The results are compared with recent predictions by a realistic band calculation.     

Anomalous luminescence of impurity-bound excitons in lithium borate crystals doped with cerium ions

The spectra and relaxation kinetics of the anomalous (?? < 10 ns) luminescence of Li₆GdB₃O₉:Ce³⁺ crystals have been experimentally detected. The time-resolved vacuum ultraviolet spectroscopy study has shown that optical transitions at 6.2 eV, caused by the transfer of an electron from the 4f ¹ ground state of Ce³⁺ to autoionizing states near the conduction band bottom of a crystal, lead to the formation of an impurity-bound exciton with the hole component localized on the 4f state of Ce³⁺ and the electron localized on states of the conduction band bottom. It has been found that the decay of such an exciton in Li₆GdB₃O₉:Ce³⁺ occurs through radiative recombination, leading to fast luminescence at 4.25 eV. The energy threshold for the formation of the impurity-bound exciton has been determined. The distribution functions of elementary relaxations over the reaction rate constants H(k), which determine the relaxation kinetics and luminescence quenching processes, have been calculated.     

Diagnose Parameters of Plasma Induced by Femtosecond Laser Pulse in Quartz and Glasses

Electron plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in quartz, fused silica, K9 glass, and Soda Lime glass was investigated by pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging have been used to determine plasma density, relaxation time, and electron collision time in the conduction band. In these materials, the electron collision time is about several femtoseconds when the electron density is in the 10¹⁹cm⁻³ range. The electron relaxation processes are different: lifetime is about 170 fs in pure quartz and fused silica, and about 100 ps in K9 and Soda Lime glass. The modified electron band by doped ions is regarded to be responsible for the difference of decay time in these materials.     

Line mixing effects in the ν2 + ν3 band of methane

This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν₂ + ν₃ band of ¹²CH₄. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν₂ + ν₃ transitions between 4410 and 4629 cm⁻¹ are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm⁻¹ atm⁻¹ at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm⁻¹ atm⁻¹ at 296 K.     

ZnO压敏陶瓷中缺陷的介电谱研究

从理论上证明了介电松弛过程在介电谱上等效于电子松弛过程,认为室温下10⁵Hz处特征损耗峰起源于耗尽层处本征缺陷所形成的电子陷阱.在-130—20℃范围内测量了三种配方ZnO陶瓷的介电频谱,发现ZnO压敏陶瓷室温下10⁵Hz处的特征损耗峰在低温下分裂为两个特征峰,认为它们起源于耗尽层中的本征缺陷(锌填隙或/和氧空位)的电子松弛过程.发现ZnO-Bi₂O₃二元系陶瓷特征峰仅仅由锌填隙引起,而ZnO-Bi_{2关键词： ZnO压敏陶瓷 本征缺陷 介电谱 热处理}     

Properties of vanadium in InP

Experiments are performed on InP/V single crystals extracted from a polycristalline ingot grown in a two zones gradient freeze furnace; in photoluminescence (PL) we observe a band with two zero phonon lines at 5692.5 cm^-1 and 5705.5 cm^-1. Photoluminescence excitation (P.L.E.) spectra have also been observed. This type of luminescence spectra has already been observed in V doped GaAs and GaP and attributed to an internal transition of V²⁺ (3 d³). D.L.T.S. and O.D.L.T.S. experiments do not reveal any deep level in the forbidden band gap. These two results seem to indicate a puzzling behaviour of V in InP as in GaAs which is discussed in the framework of a model proposed for GaAs/V : the V²⁺ ground state has a large relaxation energy and so, the excited states giving rise to the P.L. and P.L.E. spectra are not resonant with the conduction band.     

Cross sections for electron-stimulated desorption of alkali-metal atoms from adlayers on oxidized tungsten

Earlier cross-section measurements of electron-stimulated desorption (ESD) of Li, Na, K, and Cs atoms from adlayers on oxidized tungsten are analyzed with respect to substrate temperature and degree of oxidation. It is conjectured that the ESD cross sections are determined by the ratio of the rates of neutral alkali-metal re-ionization on the surface and of relaxation of the O⁺ charge in the substrate. A comparison with experiment revealed the dependence of the re-ionization rate of an alkali-metal adatom on its size and mass, as well as the dependence of the O⁺ charge relaxation rate on substrate temperature and degree of oxidation. The relation of the charge relaxation time to the substrate band structure is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1491–1497 (August 1997)