LM-OSL signals from some insulators: an analysis of the dependency of the detrapping probability on stimulation light intensity

Optically stimulated luminescence (OSL) signals from various insulators including quartz, Al2O3 : C, BeO and NaCl have been studied using the linear modulation OSL (LM-OSL) technique. LM-OSL is based on the linear increase of the stimulation light power from zero to a maximum during the measurement. The resultant OSL curve initially increases and then decays after reaching a maximum, The analysis of LM-OSL data usually assumes a linear relationship between the detrapping rate and the stimulation light intensity. However, experiments carried out using various insulators have shown that this assumption is not always correct. The initial decay rates of the blue (similar to 470 nm) light stimulated constant power OSL decay curves were examined to test the relation between the detrapping rates and the stimulation light intensity. In SiO2, Al2O3 : C and BeO a linear relation between the detrapping rates and the stimulation light intensity was observed. However the detrapping rate of the OSL signal from NaCl was non-linear. Assuming that this non-linearity can be described using a saturating exponential function, a new more general expression for the LM-OSL signal has been derived. The validity of this expression was checked using curve fitting and it was found that the new expression could describe the LM-OSL curves successfully

Optically stimulated luminescence from quartz measured using the linear modulation technique

The optically stimulated luminescence (OSL) from heated natural quartz has been investigated using the linear modulation technique (LMT), in which the excitation light intensity is increased linearly during stimulation. In contrast to conventional stimulation, which usually produces a monotonically decreasing signal, linearly increasing the stimulation power gives peaks in the signal as a function of time. In cases where the OSL signal contains more than one component, the linear increase in power of the stimulation light may result in a curve containing overlapping peaks, where the most easily stimulated component occurs at a shorter time. This allows the separation of the overlapping OSL components, which are assumed to originate from different traps. The LM-OSL curve from quartz shows an initial peak Followed by a broad one. Deconvolution using curve fitting has shown that the composite OSL curve from quartz can be approximated well by using a linear combination of first-order peaks. In addition to the three known components, i.e. fast, medium and slow components from continuous-wave-OSL studies, an additional slow component is also identified for the first time. The dose responses and thermal stabilities of the various components are also studied. (C) 2000 Elsevier Science Ltd. All rights reserved

A simple transformation for converting CW-OSL curves to LM-OSL curves

A simple mathematical transformation is introduced to convert from OSL decay curves obtained in the conventional way to those obtained using a linear modulation technique based on a linear increase of the stimulation light intensity during OSL measurement. The validity of the transformation was tested by the IR-stimulated luminescence curves from feldspars, recorded using both the conventional and the linear modulation techniques. The transformation was further applied to green-light-stimulated OSL from K and Na feldspars

OSL from beo ceramics: new observations from an old material.

In BeO ceramics, exposed to ionizing radiation, an intense OSL signal was observed. The properties of the signal and its behavior under various experimental conditions were investigated. It was found that the OSL signal is a composite signal and exhibits strong thermal quenching. The quenching energy was estimated as similar to 0.5 eV. The excitation spectrum of the OSL signal was obtained as a broad peak in the region 420-550 nm with maximum around 435 nm. The possible correlation between the OSL signal and the peaks in the TL glow curve was also examined. It was interesting to observe that the highly light sensitive TL peak near 220 degrees C does not contribute to the OSL signal. The OSL signal was found to originate from a trap near 340 degrees C. To check the possibility of using the material for radiation dosimetry the dose response and thermal stability of the OSL signal were also investigated. The dose response was found to be guile linear up to similar to 10 Gy. The thermal activation energy of the OSL trap was determined as similar to 1.7 eV using isothermal annealing and heating rate methods thus proving the suitability for dosimetry

Phototransferred thermoluminescence from alpha-Al2O3:C using blue light emitting diodes.

Phototransferred thermoluminescence (PTTL) from alpha-Al2O3:C single crystals was studied using a blue light emitting diode (LED) for phototransfer of charges from deep traps to the main dosimetry trap. The dose response was found to be linear in the region from similar to 5 mGy to similar to 5 Gy. It was observed that the corresponding deep traps were located near 500 degrees C and heating to temperatures > 600 degrees C removes the PTTL effect induced by the light from the blue LED. The thermal activation energy of the source traps involved in the PTTL production was calculated as 3.23 eV

Photo-stimulated luminescence of calcium co-doped BaFBr:Eu2+ x-ray storage phosphors

The influence of calcium co-doping on the optical properties of the x-ray storage phosphor BaFBr: Eu2+, is determined by photo- stimulated luminescence techniques. It is found that the incorporation of calcium into the lattice results in a broadening of the photo- stimulation peak due to a calcium induced FA(Br, Ca2+)-centre with stimulation maxima at 540 and 680 nm. The optical cross-sections for the photo- stimulated process are determined by utilizing stimulation light with linearly increasing intensity. Furthermore, it is shown that the sensitivity for x-rays, i.e. the number of storage centres formed during x-ray exposure, increases up to a doping level of 1 mol% while it drops rapidly at higher calcium concentrations

Frequency modulated pulsed stimulation in optically stimulated luminescence

A new pulsed-OSL stimulation unit capable of producing stimulation pulses down to 4 us wide has been developed. A matrix of 49 light emitting diodes (LEDs) are pulsed using a voltage-to-frequency converter, which produces fixed width pulses of adjustable duty cycle in the frequency range 0-10 kHz. Since the average light power falling on a sample is proportional to the repetition rate of the pulses, we have used voltage control of the frequency to undertake linearly modulated optically stimulated luminescence (LM-OSL) measurements. The frequency modulated OSL signals from various phosphors relevant to dating and retrospective dosimetry have been investigated using the new unit. (C) 2001 Elsevier Science B.V. All rights reserved