Some properties of luminescence lifetimes from quartz stimulated by blue light

Abstract

Measurements have been made of recombination lifetimes as a function of stimulation time in quartz, a natural dosimeter. Time-resolved luminescence techniques were used to study the influence on lifetimes of sustained 470nm optical stimulation of luminescence and modifications associated with beta irradiation of samples. Results are reported for samples differing in sensitivity to luminescence stimulation.     

Real-time luminescence from Al2O3 fiber dosimeters

The real-time luminescence signal from Al₂O₃ single crystal fibers, monitored during simultaneous irradiation and optical stimulation, was investigated using computer simulations and experimental measurements. Both radioluminescence (RL) and optically stimulated luminescence (OSL) signals were studied. The simulations were performed initially using a simple one-trap/one-recombination-center energy band model, and then extended to include shallow and deep electron traps as well. Real-time luminescence experiments were performed for different radiation dose rates and optical stimulation powers using periodic laser stimulation of the samples through a fiber optic cable, and the experimental results were compared with the predictions from the computer simulations. The luminescence signal was observed, both theoretically and experimentally, to increase from its initial value to a steady-state level. The steady-state RL and OSL levels were found to be dependent on dose rate, the steady-state level of the real-time OSL being independent of laser power. It was also shown that the total integrated absorbed dose throughout the irradiation period can be determined by correcting the real-time OSL signal for depletion caused by each laser stimulation pulse. The effects of the shallow and deep traps on the time-dependence of the real-time luminescence signal were studied comparing the experimental data from several Al₂O₃ fibers known to have different trapping state concentrations. The additional traps were found to slow the response of the real-time luminescence such that the time to reach steady state was increased as the additional traps were added.     

On luminescence lifetimes in quartz

In this paper we present results of investigations concerning the time dependence of luminescence emission relative to the time of stimulation in quartz. Measurements of time-resolved spectra were performed on a new versatile pulsed light emitting diode system using 525 nm stimulation, an 11 μs duration pulse, a repetition rate of 11 kHz and a 64 μs dynamic range. Effects on luminescence lifetime resulting from sample treatments such as optical stimulation, irradiation, and preheating, are reported.     

Pulsed photostimulated luminescence of alkali feldspars

The use of pulsed photostimulation techniques has a number of practical and conceptual attractions compared with continuous stimulation approaches. Enhanced signal-to-background ratios, opportunities for signal recovery techniques, and ability of detecting luminescence asynchronously and close to stimulation wavelengths are all of practical interest. In addition, it is possible to measure the time-scale and underlying physical processes of the charge transport and luminescence recombination steps following photostimulation. Proximity effects (localized transitions, tunnelling) and re-trapping can be detected directly. Facilities for pulsed photostimulated luminescence measurements using light-emitting diode (LED) arrays, laser diodes and a pulsed dye laser, with time-domain analysis down to 10^-8s have been developed. These facilities are described, together with results from studies of natural and laboratory induced signals from alkali feldspars measured at various times after irradiation. For the first time it has been shown that the recombination dynamics of irradiated feldspars consist of a complex series of continua and line components, presumed to be associated with distinct charge transport processes between traps and recombination sites. Evidence of post-irradiation modification of recombination dynamics is presented for a series of highly irradiated International Atomic Energy Agency (IAEA) F1 feldspar samples, and for a volcanic lava exhibiting gross short-term fading of both thermoluminescence and photostimulated luminescence. This provides direct evidence that fading is associated with short-range processes between trap and centre and, also for the first time, suggests an effective physically based means of detecting and potentially remedying such behaviour in dating studies.     

Real time dose rate measurements with fiber optic probes based on the RL and OSL of beryllium oxide

This work covers the examination of fiber optical probes based on the radioluminescence and real time optically stimulated luminescence of beryllium oxide. Experiments are carried out to determine the fundamental dosimetric and temporal properties of the system and evaluate its suitability for dose rate measurements in brachytherapy and other applications using non-pulsed radiation fields. For this purpose the responses of the radioluminescence and optically stimulated luminescence signal have been investigated in the dose rate range of 20 mGy/h to 3.6 Gy/h and for doses of 1 mGy up to 6 Gy. Furthermore, a new, efficient analysis procedure, the double phase reference summing, is introduced, leading to a real time optically stimulated luminescence signal. This method allows a complete compensation of the stem effect during the measurement. In contrast to previous works, the stimulation of the 1 mm cylindrical beryllium oxide detectors is performed with a symmetric function during irradiation. The investigated dose rates range from 0.3 to 3.6 Gy/h. The real time optically stimulated luminescence signal of beryllium oxide shows a dependency on both the dose rate and the applied dose. To overcome the problem of dose dependency, further experiments using higher stimulation intensities have to follow.     

The effects of low ambient temperatures on optically stimulated luminescence (OSL) processes: Relevance to OSL dating of martian sediments

Advances in luminescence dosimetry have made geochronological dating of materials from extreme environments possible through the use of optically stimulated luminescence (OSL) single-aliquot techniques. However, these environments present challenges not always encountered in routine OSL dating, such as sediments that have been stored at low, and possibly highly variable, ambient temperatures. In recent years OSL has been proposed as a method for dating recent depositional events on surfaces of other planets, specifically, Mars. As a result it has become necessary to examine the constraints that may be imposed on the OSL method by the extreme environments of extraterrestrial planetary bodies. In this paper we report on investigations of the possible effects a low storage and/or a low OSL measurement temperature could have on the OSL process and the subsequent results. Pertinent OSL properties include the stability of electron traps, the overall luminescence efficiency, and possible thermal assistance processes. The particular focus of the work is on the potential application of the OSL technique for dating surface sediments on Mars. We report the results of OSL experiments on martian simulant materials, and of generalized computer simulations of potential OSL behavior. It is concluded that the stimulation and irradiation/calibration temperatures need to be maintained fixed throughout the experiment – i.e. the dose estimation process – and that the temperature during OSL stimulation needs to be appreciably higher than the highest temperature experienced during natural irradiation. The consequences of these findings for establishing an OSL protocol and instrument package for dating martian regolith material are discussed.     

Advances in luminescence instrument systems

We report on recent advances in the development of luminescence measurement systems and techniques at Risø. These include: (1) optical stimulation units based on new-generation powerful blue light (470 nm) emitting diodes providing up to 28 mW/cm² for OSL measurements; (2) an infrared (830 nm) laser diode unit providing up to 400 mW/cm² for stimulation of feldspars; and finally (3) an optical stimulation attachment based on a focused solid state green (532 nm) laser for rapid OSL measurements of individual sand-sized single grains of a sample. Facilities for heating samples during beta irradiation and performing linearly modulated OSL measurements have also been incorporated into the system.     

Photo- and thermo-stimulated luminescence of CsI—Tl crystal after UV light irradiation at 80 K

Abstract

Thermo- and photo-stimulated luminescence are studied for CsI—Tl crystal after the irradiation with the UV light at 80 K. Creation spectrum of the photostimulated luminescence coincides with the D absorption band of Tl⁺ ions. Nature of the defects created by UV light at low temperatures is discussed basing on the correspondence between the thermostimulated glow curve peaks and thermal evolution of the photostimulation spectra observed after irradiation in the D absorption band. Three bands at 1400, 950 and 580 nm have been observed in the stimulation spectrum at 80 K. The 1400 and 950 nm stimulation bands are presumably explained as the optical transitions in the Tl⁰ centre forming the spatially correlated defect pair with V_k centre while the 580 nm stimulation band is connected with the unperturbed Tl⁰ centres. It is concluded that the Tl⁺ luminescence at low temperature is connected with the electron recombination with the Tl²⁺ centre.     

The influence of optical bleaching on lifetimes and luminescence intensity in the slow component of optically stimulated luminescence of natural quartz from Nigeria

The intensity of optically stimulated luminescence may be decreased to a slow or medium component of its decay curve by optical bleaching, that is, by prolonged exposure of the luminescent sample to stimulating light. In this paper, we report on the influence of irradiation and measurement temperature on luminescence lifetimes as well as on the effect of measurement temperature on luminescence intensity in annealed natural quartz from Nigeria. Measurements were carried out in the slow component region using time-resolved optical stimulation at 470 nm on samples annealed at 500 and 600 °C. Luminescence lifetimes were determined from the resultant time-resolved luminescence spectra by analysing the portion of each spectrum after the stimulating light pulse of duration 11 μs. In preparatory tests, the influence of the duration of optical bleaching on lifetimes was investigated. It was found that lifetimes in samples annealed at 500 °C are independent of the duration of optical bleaching, whereas lifetimes in quartz annealed at 600 °C are affected, decreasing towards a constant value with duration of bleaching. Concerning measurements in the slow-component region, lifetimes were found to decrease with irradiation dose for samples annealed at either 500 or 600 °C. The temperature dependence of lifetimes in both sets of quartz is similar with lifetimes constant at about 36 μs between 20 and 120 °C, but decreasing consistently from then on to about 5 μs at 200 °C, the maximum measurement temperature used in experiments. The luminescence intensity was observed to typically go through a peak as the stimulation temperature was increased from 20 to 200 °C, following a brief initial decrease, a change better exemplified in the quartz annealed at 600 °C. The initial decrease in luminescence intensity is attributed to the dominance of optical stimulation over thermal stimulation. On the other hand, the subsequent change of luminescence intensity with temperature is discussed as evidence of thermal assistance to optical stimulation, initially with activation energy of 0.27±0.07 eV and of thermal quenching subsequently with activation energy equal to 0.93±0.23 eV for samples annealed at either 500 or 600 °C. The temperature dependence of lifetimes is explained as showing increased thermal effect on lifetimes with activation energy values within 0.83±0.01 eV. On the other hand, the influence of irradiation on lifetimes is accounted for in terms of an energy band model for quartz consisting of three luminescence centres and one non-radiative recombination centre.     

New luminescence measurement facilities in retrospective dosimetry

This paper gives a review of recent developments in luminescence measurement facilities on the Risø TL/OSL reader including radio-luminescence (RL), exo-electron and violet stimulation attachments, and a method for characterising and if necessary correcting for beta irradiation source non-uniformity.We first describe improvements to the existing RL option to allow near infra-red detection (NIR) during irradiation by the built-in ⁹⁰Sr/⁹⁰Y beta source. The RL optical signal is collected by a liquid light guide through an F34-901 interference filter and detection is based on a dedicated thermoelectrically cooled NIR sensitive PMT (detection window peak at 855 nm, FWHM 27 nm). Software and electronics have been modified to allow standard TL and OSL measurements in the same sequence as RL measurements. Together with a new bleaching source based on a high-power UV LED (395 nm; 700 mW/cm²), this facility has been used to measure natural doses in feldspar using the decaying NIR RL signal.Secondly, we present a method for mapping radiation field of the built-in ⁹⁰Sr/⁹⁰Y β-source and estimating grain-location specific dose-rates. This is important for the accuracy of single grain results, when radiation field is spatially non-uniform across the sample area. We document the effect of this correction method and further investigate on the effect of lifting the source to achieve a better dose-rate uniformity.Finally we summarise two recently-developed novel facilities to help investigate (i) the time scales involved in OSL processes (time-resolved exo-electron detection) and (ii) extending the age range (violet stimulated signals from deep quartz OSL traps).     

Use of Secondary Phosphorescence for Determining an Absorbed Dose in Dosimetric Luminophors

We consider the method of measuring optically stimulated persistence for radiation dosimetry based on separation in time of stimulating irradiation and of the recording of luminescence response. It is shown that here stimulation by shortwave radiation is possible, which is overlapped in the spectrum with the dosimetric luminophor radiation. We have measured the spectra of stimulation of a number of industrial dosimetric luminophors. The special features of the recording of optically stimulated persistence are discussed for the luminophors that contain manganese (Mn²⁺) as an activator and for which the time of decay of the luminescence which is excited within the centers is 40–50 msec. The method is applicable to the dosimetry of natural varieties of quartz for dating corresponding deposits.     

Luminescence properties of biotite relevant to dating and dosimetry

Biotite mineral grains from granitic rocks were subjected to luminescence studies with optical and thermal stimulation. Moderate thermoluminescence (TL) signals and weak optically stimulated luminescence (OSL) with blue-green light stimulation were detected after 50 Gy beta irradiation. No detectable infrared-stimulated luminescence (IRSL) was observed for natural and laboratory beta-irradiated samples. TL peaks at 118, 300, 360 and 480 °C can be identified from laboratory-irradiated samples. The 360 °C TL peak saturates at a higher dose than quartz, but shows significant anomalous fading after 80 days stored at room temperature. The potentials and problems for biotite used as a natural dosimeter are discussed.     

Scintillation and optical stimulated luminescence of Ce-doped CaF2

Scintillation and optical stimulated luminescence of Ce 0.1–20% doped CaF₂ crystals prepared by Tokuyama Corp. were investigated. In X-ray induced scintillation spectra, luminescence due to Ce³⁺ 5d–4f transition appeared around 320 nm with typically 40 ns decay time. By ²⁴¹Am 5.5 MeV α-ray irradiation, 0.1% doped one showed the highest scintillation light yield and the light yield monotonically decreased with Ce concentrations. Optically stimulated luminescence after X-ray irradiation was observed around 320 nm under 550 or 830 nm stimulation in all samples. As a result, intensities of optically stimulated luminescence were proportional to Ce concentrations. Consequently, scintillation and optically stimulated luminescence resulted to have a complementary relation in Ce-doped CaF₂ system.     

Spectral information from minerals relevant for luminescence dating

The paper reviews basic spectral features of luminescence from minerals used in dating and allied research. Luminescence production is a result of multiple interactions within the imperfect crystal lattice and spectral information is not limited to the emission of light. Results of spectral investigations of luminescence emission during thermal stimulation (TL) or optical stimulation (OSL) form the main part of the paper. However, information on luminescence excitation and light absorption spectroscopy is also presented and possible links between luminescence production in minerals and particular lattice defects are considered. Quartz and feldspars, the most commonly used minerals, receive special attention, but the review includes other materials such as polymineral fine-grained fractions from sediments, zircon, calcite and other salts (halite, sulfate), meteorites, flint, volcanic materials (obsidian, tephra), ceramics and metallurgical slags. Although a wide range of different luminescence emission wavebands occur, it can be shown that certain emissions dominate in particular materials. Basic dosimetric properties are often known just for single emission wavebands of a particular mineral, and are listed in this case. The paper also aims to provide a starting point and inspiration for the study of other TL and OSL emissions, with particular regard to their potential and suitability for dating and related dosimetry tasks. These investigations, involving palaeodose determination based on an emission waveband with known characteristics, need careful separation of the particular emission peak, which may be influenced by its behaviour during the dating procedure (sample preparation, irradiation, preheat treatments, luminescence measurements, etc.). Spectral information available in this context and some technical remarks on the experimental conditions will be given to pave the way for conventional TL or OSL measurements in luminescence dating and dosimetry using natural or semi-natural materials.     

Proton-irradiation effect on the luminescence of the MEH-PPV conjugated polymer

We report proton-irradiation effect on luminescence in the MEH-PPV conjugated polymer. While the luminescence was severely weakened by the low-energy irradiation with a high dosage, it was affected only weakly by the high-energy irradiation with a low dosage. The electroluminescence was affected by the irradiation more severely than the photoluminescence was, preserving the external quantum efficiency. While the luminescence spectrum of the severely damaged polymer was broadened with a blue-shift, a weak damage resulted only in a decrease in the luminescence intensity apparently preserving the spectral shape. The change in the luminescence spectra may be explained by chain conformational disorders as well as chain scission induced by the irradiation.     

Comparison of luminescence lifetimes in quartz following alpha and beta irradiation

The change in optically stimulated luminescence sensitivity of quartz associated with annealing is accompanied by a change in luminescence lifetime, whereas, in contrast, the change in sensitivity associated with irradiation by alpha particles rather than by beta particles is not accompanied by any change in luminescence lifetime. This is compatible with the usual ‘saturation’ explanation for the significantly lower luminescence sensitivity of quartz to alpha irradiation compared to the luminescence sensitivity to beta irradiation.     

BaFCl:Eu2+中F色心的浓度和光激励截面与温度和紫外线的辐照波长的关系

本文研究了BaFCl:Eu²⁺在不同波长的紫外线辐照和不同的测定温度下的光激励发光性质.通过改变激励方式及激励光的扫描方向,给出了BaFCl:Eu²⁺光激励发光过程中,两种F色心的浓度比值和光激励截面比值与紫外线辐照波长和测定温度的关系.同时我们还研究了在激励读出过程中,对应两种F色心的光激励发光强度与激励温度的关系,并且给出了相应于F(Cl^-)心的热激活能.     

强脉冲软X光辐照薄塑料闪烁体发光特性研究

 介绍了Z-pinch实验用软X光功率仪的测量原理,利用“强光一号”产生的强脉冲软X光对薄塑料闪烁体(Ø40 mm×0.1 mm)进行了辐照。实验中,采用两套软X光功率仪并安装在同一个大法兰面上,其中一套作为标准系统,参数保持不变,另一套系统的狭缝宽度逐渐增加,以改变软X光辐照到闪烁体上的能量通量密度。测量了软X光的辐射功率,由此计算得到在强脉冲软X光辐照下发光线性输出时能量通量密度下限,为1.47×10⁵ W/cm²,为以后在Z-pinch物理诊断中合理安排探测系统提供了实验依据,使诊断结果更加合理和准确。     

LiBaF3 as a thermal neutron scintillator

We report on the scintillation properties of LiBaF₃ upon irradiation with thermal neutrons. For thermal neutron excitation cross luminescence is not observed, contrary to luminescence under X-ray or γ-ray excitation.     

Optimal spectral phase control of femtosecond laser-induced up-conversion luminescence in Sm3+:NaYF4 glass

The spectral phase of the femtosecond laser field is an important parameter that affects the up-conversion(UC)luminescence efficiency of dopant lanthanide ions.In this work,we report an experi-mental study on controlling the UC lmiiinescence efficiency in Sm^3+:NaYF4 glass by 800-nm femtosec-ond laser pulse shaping using spectral phase modulation.The optimal phase control strategy efficiently enhances or suppresses the UC luminescence intensity.Based on the laser-power dependence of the UC luminescence intensity and its comparison with the luminescence spectrum under direct 266-nm fem-tosecond lciser irradiation,we propose herein an excitation model combining non-resonant two-photon absorption with resonance-media ted three-photon absorption to explain the experimental observations.