Analysis of optical bleaching of OSL signal in sediment quartz

The aim of this work was to study the effect of the quality of optical bleaching on the results of OSL (Optically Stimulated Luminescence) dating method. The large aliquots of coarse quartz grains extracted from fluvial deposit were used in the study. The poor, medium and good bleaching were simulated in laboratory with help of Blue LED light source in series of experiments. Then the samples were irradiated with a common laboratory dose. The equivalent doses (DE) were measured by the help of standard Single Aliquot Regeneration (SAR) technique, but obtained DE distributions are analyzed in a new way. The method for recognizing and compensating for partial bleaching is proposed. The conclusions for dating sediment quartz samples are presented and discussed.     

Investigation on competition between the input signal and noise in a Brillouin amplifier

We theoretically and experimentally investigate the competition mechanism between the input signal and noise in a Brillouin amplifier, and the influence of the delay time of the pump pulse relative to the signal pulse on this competition. Results show that as the input signal intensity increases, the amplified Brillouin scattering (ABS) noise gradually weakens, while the signal amplification predominates. When the ratio of the input signal to the pump intensity is greater than 10⁻⁴, the ABS noise will be almost completely suppressed. The delay time should be controlled as the pump pulse half-width to achieve high signal-noise-ratio and high amplification.     

Zeroing of the OSL signal in quartz from young glaciofluvial sediments

The natural luminescence of quartz samples from recent (<200 yr old) glaciofluvial sediments collected from a range of distances from the snout of the Gangotri glacier in the Garhwal Himalaya, India, was measured. Six measured D_E (equivalent dose) values ranged from 35 to 175 Gy, strongly suggesting that these samples had been exposed to daylight only poorly before deposition. However, regenerated growth curves constructed after exposure to several hours of natural daylight gave apparent D_E values ranging from 10 to 30 Gy. Detailed measurements of one sample confirm that these observations are due to a huge recuperation effect. The “shine plateaux” observed in the majority of these D_E determinations showed little increase of D_E with increasing exposure time. The mechanisms of this unexpected behaviour, and the implications for the detection of partial bleaching, are discussed.     

Observations of thermal transfer OSL signals in glacigenic quartz

The conclusions of Rhodes and Pownall (Rhodes, E.J., Pownall, L., 1994. Zeroing of the OSL signal in quartz from young glaciofluvial sediments. Radiation Measurements 23, 329–333) were somewhat discouraging for the prospects of using quartz OSL for dating glacigenic sediments, while the more detailed study of Rhodes and Bailey (Rhodes, E.J., Bailey, R.M., 1997. The effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments. Quaternary Science Reviews (Quaternary Geochronology) 16, 291–298) provided more encouragement. Specifically, the latter authors were able to account for the relatively high D_e values observed for recent glacigenic (dominantly glaciofluvial) sediments in terms of an anomalously high thermal transfer effect, rather than simply insufficient bleaching prior to deposition. In other locations, the OSL of quartz from glacigenic material appears to provide reliable age estimates, and does not suffer from these effects (Owen, L.A., Richards, B., Rhodes, E.J., Cunningham, W.D., Windley, B.F., Badamgarav, J., Dorjnamjaa, D., 1998. Relic permofrost structures in the Gobi of Mongolia: age and significance. Journal of Quaternary Science 13 (16), 539–548; Richards, B.W., Owen, L.A., Rhodes, E.J., 2000. Timing of Late Quaternary glaciations in the Himalayas of northern Pakistan. Journal of Quaternary Science 15, 283–297). In this paper, laboratory bleached samples from both the above studies are remeasured, using an experimental design to correct for OSL sensitivity changes, which has some similarities to the single aliquot regenerative dose (SAR) protocol of Murray and Wintle (Murray A.S., Wintle A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73). Clear evidence of thermal transfer OSL signals, generated during the preheating procedure, is presented. Further measurements, using the full SAR protocol, demonstrate that the source of this charge is related to natural dosing. For one sample, the apparent effect is subtracted effectively by the SAR protocol. Another sample studied in detail shows a striking relationship between the thermally transferred OSL signal and the total TL observed during the ramping of the preceding preheat treatment.     

The influence of pressure on recombination centres in piezoelectric luminophores

The present paper shows that a recombination centre of the Cu⁺-[S^–] type in the ZnS lattice has local piezoelectric properties. On the basis of this fact some phenomena of triboluminescence are explained and a periodic generator of light is proposed.     

Influence of thermal treatment on OSL regeneration in potassium chloride

Optically stimulated luminescence (OSL) of pure analytical potassium chloride (KCl) prepared in two different forms (crystals and pellets) was studied. The occurrence of regeneration effect (self-renewal of the OSL signal) in the material was examined. The experiments using the variable delay OSL (VD-OSL) method were carried out. Performed measurements allowed to determine time scale of the phenomenon, as well as quantitative changes of regeneration depending on thermal treatment before and after irradiation. Significant increase of the OSL regeneration was noticeable for pellets after the application of the annealing before irradiation, while for crystals a substantial decrease of regeneration was observed. Preheating applied after irradiation caused that self-renewal of OSL signal was drastically reduced or completely suppressed depending on the form of KCl samples.     

Theory of the non-radiative recombination of electrons at perturbation centres in polar crystals

Non-radiative recombination of electrons at a perturbation centre in a polar crystal is considered as a single phonon transition of a polaron in a non-adiabatic approximation from the continuous spectrum to the discrete excited state in a perturbation centre. The perturbation causing a transition is taken as the interaction of a polaron with a free phonon field leading to the production and disappearance of phonons in the neighbourhood of the perturbation centre. Calculation is carried out of the recombination coefficient and the effective cross-section for recombination as a function of the temperature for perturbation centres of the Coulomb type in crystals of ZnS.     

Assessing the impact of pulsed-irradiation procedures on the thermally transferred OSL signal in quartz

Thermally transferred optically stimulated luminescence (TT-OSL) dating protocols have been suggested as a means of extending the age range of luminescence dating. Several studies demonstrate that TT-OSL signals increase with large radiation doses (>2000 Gy) and yet, few studies report older TT-OSL ages (>400 Gy) in agreement with independent absolute age control. In one such study, agreement with independent chronology was only achieved for the old samples by implementing a pulsed-irradiation procedure. Pulsed-irradiation is suggested to compensate for dose rate dependent competition effects by dividing the laboratory irradiation into discrete irradiation steps interspersed with heat treatments. However, every inter-step heat treatment has the potential to anneal part of the TT-OSL dating signal. This study compares constant- and pulsed-irradiation TT-OSL protocols and investigates the degree of partial thermal annealing. The results suggest that almost all of the difference in outcome between constant- and pulsed-irradiation protocols can be explained by partial annealing of the TT-OSL signal rather than by competition effects. Partial annealing distorts the laboratory dose response curve but has no impact on the natural signal, resulting in unreliable equivalent dose estimates. This means that pulsed-irradiation procedures may not be viable for TT-OSL dating measurements. Future studies implementing pulsed-irradiation procedures should carefully consider the extent to which inter-step thermal treatments partially anneal the signal.     

On the effective cross-section for recombination of free carriers with dipole centres

An approximate calculation of the effective cross-section for recombination δ_eff of free charge carriers with dipole centres for small mean path lenght l of free carriers and not very small gas-kinetical cross-section of recombination σ_k is conducted. A formula for the σ_eff suitable also for larger l and small σ_k is suggested.     

On the determination of the position of the energy level of surface recombination centres

A detailed analysis of the dependence of the surface recombination velocitys on the surface potential _s leads to the conclusion that the position of the surface recombination level with respect to the centre of the energy gapE _t -E _i does not coincide with the valueq _s *, while the surface recombination velocitys decreases to half its maximum value. The difference between the two quantities is negligible only when the width of the curves( _s ) between the points corresponding to the valuess=1/2s _max is greater than 8kT.

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s _s , E _t -E _{i s} , s . , s( _s ) , s=1/2s _max, 8kT.

     

Anomalous thermal bleaching of color centers in calcium fluorapatite

A study has been made of the radiation-induced paramagnetic color centers in calcium fluorapatite on annealing. It is found that there is an anomalous increase in the center concentration during isothermal annealing. An explanation is given via a model for diffusion of point defects and groups involving charge redistribution. It is found that the dislocation structure affects the thermal bleaching of the color centers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 34–37, April, 1975.     

Transient competition between photocatalysis and carrier recombination in TiO_2 nanotube film loaded with Au nanoparticles

Highly ordered TiO2 nanotube array(TNA) films are fabricated by using an anodic oxidation method. Au nanoparticles(NPs) films are decorated onto the top of TNA films with the aid of ion-sputtering and thermal annealing. An enhanced photocatalytic activity under ultraviolet C(UVC, 266 nm) light irradiation is obtained compared with that of the pristine TNA, which is shown by the steady-state photoluminescence(PL) spectra. Furthermore, a distinct blue shift in the nanosecond time-resolved transient photoluminescence(NTRT-PL) spectra is observed. Such a phenomenon could be well explained by considering the competition between the surface photocatalytic process and the recombination of the photo-generated carriers. The enhanced UV photocatalytic activities of the Au–TNA composite are evaluated through photo-degradation of methyl orange(MO) in an aqueous solution with ultraviolet–visible absorption spectrometry. Our current work may provide a simple strategy to synthesize defect-related composite photocatalytic devices.     

The role of residual technological impurities in the formation of radiative recombination centres in irradiated germanium

A comparison study of the photoluminescent (PL) spectra in pure and ultra-pure irradiated and annealed germanium has been performed. Some radiative recombination centres including impurities have been found. The spectra of samples bombarded by neutrons were found to include, along with the lines from intrinsic defects (Z, Y, X, W, V), the centres due to hydrogen and oxygen impurities (the lines T₁, T₂, U). A considerable number of the lines (A₁-A₃, B₁, B₂, C, D₁, D₂) in the PL spectra of crystals exposed to gamma-quanta and electrons were identified with the centres including carbon atoms. Such a great set of lines, presumably, results from the transformation of the above mentioned complexes in the course of annealing. The observed differences in the PL spectra within 0.72 to 0.74 eV range probably indicate a contribution of several types of intrinsic defects and other impurities, along with carbon, to complexing.     

Derivation of a closed form analytical expression for fluorescence recovery after photo bleaching in the case of continuous bleaching during read out

Measurements of very slow diffusive processes in membranes, like the diffusion of integral membrane proteins, by fluorescence recovery after photo bleaching (FRAP) are hampered by bleaching of the probe during the read out of the fluorescence recovery. In the limit of long observation time (very slow diffusion as in the case of large membrane proteins), this bleaching may cause errors to the recovery function and thus provides error-prone diffusion coefficients. In this work we present a new approach to a two-dimensional closed form analytical solution of the reaction-diffusion equation, based on the addition of a dissipative term to the conventional diffusion equation. The calculation was done assuming (i) a Gaussian laser beam profile for bleaching the spot and (ii) that the fluorescence intensity profile emerging from the spot can be approximated by a two-dimensional Gaussian. The detection scheme derived from the analytical solution allows for diffusion measurements without the constraint of observation bleaching. Recovery curves of experimental FRAP data obtained under non-negligible read-out bleaching for native membranes (rabbit endoplasmic reticulum) on a planar solid support showed excellent agreement with the analytical solution and allowed the calculation of the lipid diffusion coefficient.     

Collective thermal emission of electrons from deep centres in GaAs

A treatment of the thermal emission of electrons from deep centers as a collective process is presented. In contrast to the conventional theory our concept leads to a non-exponential approach of the system to a new equilibrium state. Such decays have indeed been observed in our work.     

Direct spectroscopic evidence for competition between thermal molecular agitation and magnetic field in a tetrameric protein in aqueous solution

Samples of a typical tetrameric protein, the hemoglobin, at the concentration of 150 mg/ml in bidistilled water solution, were exposed to a uniform magnetic field at 200 mT at different temperatures of ${15}^{°}\text{C}$, ${40}^{°}\text{C}$ and ${65}^{°}\text{C}$. Fourier Transform Infrared Spectroscopy was used to analyze the response of the secondary structure of the protein to both stress agents, heating and static magnetic field. The most relevant result which was observed was the significant increasing in intensity of the Amide I band after exposure to the uniform magnetic field at the room temperature of ${15}^{°}\text{C}$. This result can be explained assuming that protein's α-helices aligned along the direction of the applied magnetic field due to their large dipole moment, inducing the alignment of the entire protein. Increasing of temperature up to ${40}^{°}\text{C}$ and ${65}^{°}\text{C}$ induced a significant reduction of the increasing in intensity of the Amide I band. This effect may be easily explained assuming that Brownian motion of the protein in water solution caused by thermal molecular agitation increased with increasing of temperature, contrasting the effect of the torque of the magnetic field applied to the protein in water solution.     

Assessing the impact of IR stimulation at increasing temperatures to the OSL signal of contaminated quartz

The purpose of the present study is to identify the effect of the increasing temperature IR stimulation to the component-resolved OSL luminescence signal of mixed quartz-feldspars material. Post IR OSL signals measured at 110 °C were analysed via only general order kinetic terms, while IR signals obtained at increasing temperatures were de-convolved using the sum of general order kinetics plus a tunnelling component. By increasing stimulation temperature, it was demonstrated that IRSL at temperatures above 50 °C does not only stimulate feldspar but also stimulates both fast and medium quartz OSL components. In the temperature range between 175 and 250 °C, the IRSL initial intensity is dominated by the fast OSL component. Estimated equivalent doses using either Post-IR₁₇₅.OSL₁₁₀ as well as IRSL₁₇₅ (with the indices indicating the measurement temperature) are in good agreement between each other, due to both stimulating quartz. Finally, the physical meaningfulness of the fitting parameters for the tunnelling component is also discussed.     

On the dielectric loss and thermal bleaching of calcite irradiated by X-rays

The changes produced by X-ray irradiation in the dielectric and optical properties of calcite crystals are reported. At ordinary temperatures, the dielectric constant as well as the dielectric loss of the uncoloured crystal remains practically unchanged in the frequency region of 10 kc/s-15 Mc/s. It has been found that the temperature variation of its dielectric loss can be represented by an equation tan where A and B are constants; this is attributed to the movement of vacancies in the crystal.

On irradiation by X-rays, calcite exhibits pronounced optical absorption in the ultraviolet region beyond 400 mμ; the dielectric loss of calcite also increases considerably on colouration. The thermoluminescence shows a very strong glow peak at 85°C with minor ones at higher temperatures. During thermal bleaching, the dielectric loss of the coloured crystal shows a prominent maximum in the temperature range 70–120°C and beyond 230°C, it varies in the same way as in the case of the uncoloured crystal. The correspondence between the change in dielectric loss and the first glow peak is possibly due to thermal release of trapped electrons. The optical absorption disappears when the crystal is heated to 350°C and on cooling to room temperature, its dielectric loss returns to its original value before colouration.