The optical dynamics of a doped amorphous system, tetra-tert-butylterrylene in amorphous polyisobutylene, has been experimentally studied by the spectra of single impurity molecules measured at temperatures of 2, 4.5, 7, and 15 K. The study of the temporal evolution of the fluorescence excitation spectra of the molecules under consideration made it possible to unambiguously establish the individual identity of the spectra of particular molecules and to analyze their multiplet structure. Repeated scanning of a selected spectral range with subsequent summation of the data made it possible to considerably reduce the errors that arise upon single scanning of the spectra of single molecules. The majority of the spectral trails detected were in agreement with the model of two-level systems. Jumps of spectral lines due to transitions in such systems were observed at all temperatures. 相似文献
Manifestations in the spectra of impurity chromophore molecules in a disordered solid matrix of the interaction of these molecules with two-level systems (TLSs) of the matrix are analyzed. The characteristic distances within the limits of which the interaction between TLSs and an impurity molecule leads, in the main, to either splitting or broadening of the spectrum, as well as the distance beginning with which this interaction is practically undetectable, are determined. Information about the effective value of the minimal distance between impurity molecules and TLSs, which is caused by nonzero sizes of the molecules and the TLSs, is presented. The analysis is performed by a statistical processing of experimental and model spectra of single tetra-tert-butylterrylene molecules in amorphous polyisobutylene at a temperature of 2 K, when the contribution of quasi-local low-frequency vibrational modes of the matrix to these spectra can be neglected. 相似文献
A new method for measuring low-temperature absorption spectra of single impurity molecules using a laser confocal polarized-light transmission microscope is proposed. The sensitivity of this method is of the same order of magnitude as that of fluorescence excitation spectroscopy. Combined use of both methods makes it possible to study distributions of impurity molecules by the magnitude of fluorescence quantum yield and their correlations with the linewidth distributions, as well as to determine if spectral jumps lead to changes in the fluorescence quantum yield. 相似文献
This paper reports on measurements of fluorescence excitation spectra of single impurity molecules of terrylene in n-decane at T=1.7 K. Spectra measured within the same spectral interval but at consecutive instants of time exhibit zero-phonon (ZP) lines of single impurity molecules of several species, differing in the behavior of the line shape and frequency in time. On the one hand, one observes stable ZP lines, well approximated with a Lorentzian. On the other, one sees spectral features with a profile varying from one spectrum to another, with only individual fragments of such a profile allowing the Lorentzian approximation; such features are interpreted assuming the presence of unstable impurity molecules, the ZP lines of which display small (a few tens of MHz) spectral jumps with a time interval of about 10 s. Such molecules exhibit a substantial decrease in the spectral jump frequency within a measurement period of the order of 5000 s, which is attributed to a decrease in the contribution due to spectral diffusion resulting from sample structure relaxation. 相似文献
Laser-induced breakdown spectroscopy (LIBS) has been evaluated for on-line, simultaneous multi-species impurity monitoring in hydrogen. A miniature spectrometer with spectral coverage of 620–800 nm and a gated detection system with spectral coverage of 40 nm were both used to record LIBS spectra from the spark produced in sample gas by a frequency-doubled Nd YAG laser. The effect of pressure on detecting the impurity (e.g., nitrogen, argon, and oxygen) in hydrogen was studied. LIBS spectra with different impurity levels of nitrogen, argon, and oxygen were recorded, and the intensity of the spectral lines of Ar, O, N, and H observed were used to form calibration plots for impurity measurement. The limits of detection (LODs) for oxygen, argon, and nitrogen in hydrogen were estimated from the calibration obtained with both the gated and ungated detection. The hydrogen impurity measurements based on the ungated miniature system show reliable and reproductive results. But the LODs with this system are about four times higher than the LODs obtained with a gated detection system in this work. 相似文献
We analyze microscopically the valence and impurity band models of ferromagnetic (Ga,Mn)As. We find that the tight-binding Anderson approach with conventional parametrization and the full potential local-density approximation+U calculations give a very similar band structure whose microscopic spectral character is consistent with the physical premise of the k·p kinetic-exchange model. On the other hand, the various models with a band structure comprising an impurity band detached from the valence band assume mutually incompatible microscopic spectral character. By adapting the tight-binding Anderson calculations individually to each of the impurity band pictures in the single Mn impurity limit and then by exploring the entire doping range, we find that a detached impurity band does not persist in any of these models in ferromagnetic (Ga,Mn)As. 相似文献
The purely electronic linewidth δ of terrylene impurity molecules in monocrystalline biphenyl is studied at temperatures T between 1.7 and 3.5 K using the technique of single-molecule spectroscopy (SMS). Based on the data obtained, individual molecules appear to have their own law of δ(T) dependence; further, hysteresis effects have been observed in thermocycling experiments. The single-molecule (SM) lines investigated quickly broaden and vanish at temperatures between 3 and 3.5 K and reappear after the sample is cooled down again. At T≈2 K, a slow process of spectral diffusion (SD) was observed on timescales longer than 10 s. To learn about the role of faster SD processes, the technique of intensity-time-frequency correlation (ITFC) SMS was applied to a stable SM line after it had been broadened by 75% as a result of a thermocycling experiment. At 2 and 2.3 K, no significant line broadening could be revealed on timescales between 0.16 ms and 10 s. 相似文献
We report the first measurement of the density of states of low-energy vibrational excitations in a disordered solid via single-molecule (SM) spectroscopy. Optical spectra of many single tetra-tert-butylterrylene (TBT) molecules embedded to amorphous polyisobutylene (PIB) as spectral probes were recorded at low temperatures. The T dependences of SM spectral linewidths showed the broad distribution of local frequencies of vibrations under study. The obtained distribution was compared with the "Boson peak" in pure PIB measured in [R. Inoue, J. Chem. Phys. 95, 5332 (1991)] by neutron scattering. We found that embedding of a small amount of TBT into PIB does not influence markedly on the observed vibrational dynamics. These results prove the local character of low-energy vibrational excitations in glasses and the existence of relationship between these excitations and the Boson peak. 相似文献
The photon echo (PE) spectroscopy and single‐molecule spectroscopy (SMS) may be combined to give a very powerful tool for comprehensive study of low‐temperature dynamics in dye‐doped disordered solids (polymers, glasses). At the same time, this type of studies are likely to reveal discrepancies when comparing characteristic times of optical dephasing T2 and single‐molecule zero‐phonon spectral lines (ZPL) broadening obtained from PE and SMS, correspondingly, for tetra‐tert‐butylterrylene in polyisobutylene in the temperature range of a few–dozen of Kelvins [see Phys. Status Solidi B 241 , 3480 and 3487 (2004)]. Inexplicably, PE‐experiments demonstrated T2‐times to be much shorter than it is sufficient to cause the corresponding ZPL broadening. Here we experimentally solve this problem and show that at T = 4.5–15 K the incoherent PE gives T2‐times which correspond to the narrowest SM ZPL. On the SM‐level there is a pronounced additional ZPL‐broadening due to spectral diffusion processes which are strongly dependent on the characteristics time of the measurement (tens of nanoseconds for PE and seconds for SMS). There is also a broad distribution of ZPL spectral widths for different SMs due to different local environments, that contribute differently to both the optical dephasing and the spectral diffusion processes, but always in addition to the value of inverse optical dephasing times measured using a PE technique.
The results of a statistical analysis of the spectra of single molecules of tetra-tert-butylterrylene in amorphous polyisobutylene at temperatures of 2, 4.5, and 7 K are presented. Model calculations of such spectra for this system are performed in the context of the stochastic theory of the spectra of single molecules in lowtemperature glasses. Analysis of the multiplet structure of the experimental and model spectra made it possible to obtain data about the minimal distance between impurity chromophore molecules and two-level systems and about the distribution parameters of their coupling constant. The interaction of a chromophore with quasilocal low-frequency vibrational modes of the matrix was found to influence the structure and parameters of the spectra observed. The model calculations performed showed that the specific structure of the spectra of single molecules at low temperatures is determined by the interactions with a small number of nearby two-level systems. 相似文献
Photosensitive EPR measurements ofS-state centers of gallium and tin in ZnTe single crystals are reported. In addition to large hyperfine interaction with the impurity nuclei the spectra show partially resolved superhyperfine structures arising from three shells of tellurium ligands. Both HF and SHF splittings decrease with increasing temperature. The samples exhibitp-type photoconductivity with the same spectral sensitivity observed with the generation and depletion of the EPR-spectrum. 相似文献
We demonstrate experimentally that structural perturbations imposed on highly dispersive photonic crystal-based waveguides give rise to spectral features that bear signatures of Anderson localization. Sharp resonances with effective Q's of over 30 000 are found in scattering spectra of disordered waveguides. The resonances are observed in a approximately 20-nm bandwidth centered at the cutoff of slowly guided Bloch modes. The origin of the spectral features can be explained by the interference of coherently scattered electromagnetic waves which results in the formation of a narrow impurity (or localization) band populated with spectrally distinct quasistates. Standard photon localization criteria are fulfilled in the localization band. 相似文献
Expressions are obtained for the components of the permittivity tensor in the optical region for a nematic liquid crystal with impurity molecules having the internal rotation conformational degree of freedom. The dependence of the intensity and dichroism of the impurity absorption bands in isotropic and nematic phases on the parameters of conformational, orientation, and mixed conformation-orientation orders of molecules is found. The influence of the mutual correlation of conformational and orientation degrees of freedom of molecules on these parameters is studied. The dependence of the oscillator strengths of molecular transitions on the phase state of a medium and the orientation order of the impurity subsystem is analyzed. The self-consistent nature of molecular, structural, and spectral changes upon the nematic-isotropic liquid phase transition is demonstrated. 相似文献
This paper presents the technique and results of the investigation of the structural relaxation in disordered solid media (polyisobutylene, toluene, ortho-dichlorobenzene) at temperatures below the glass transition point via the spectra and fluorescence images of single impurity fluorescent molecules (terrylene, tetra-tert-butylterrylene). Application of the thermal-cycling method has made it possible to significantly extend the temperature range of investigation (from 4.5 K to the glass transition temperature). The changes observed in individual parameters of low-energy elementary excitations of the tunneling and vibrational types due to structural relaxation processes have been studied. It has been found that there is a spatial inhomogeneity in the distribution of the activation temperatures of local relaxation processes. 相似文献
Core-level and valence-band photoelectron spectra and Auger spectra for the basal plane of highly ordered graphite, the edge plane of highly ordered graphite, the basal plane of graphite oxide, and for the basal plane of disordered graphite are compared in an effort to determine spectral features that may be used to identify these chemical species in carbon-rich specimens. The photoelectron spectra were recorded using 1253.6 eV X-ray excitation. The Auger spectra were obtained using both X-ray (1253.6 eV) and electron (3 keV) excitation. The differential X-ray excited C-KVV spectra were the most useful in distinguishing the different types of carbon. In particular, the plasmon structure and the energy separation between the two major excursions were very sensitive to changes in the surface chemistry and structure. Changes in peak position and peak width observed in the valence band and C(1s) photoelectron spectra were also very helpful in distinguishing the pristine, structurally damaged, and the oxidized graphite surfaces. Much of the structural and chemical information apparent in the X-ray excited C-KVV spectra was lost upon electron beam exposure. Differences in the C-KVV Auger lineshapes for X-ray and electron excitation were attributed to both structural and chemical changes induced by electron beam exposure. 相似文献