Takao Sakurai

Evidence of continuous trap distribution in the glow curve of a Brown microcline

The formidable task of determining a mathematical form of the trap distribution in a solid has been solved for the case of an unusually broad thermoluminescence (TL) glow peak of a Brown microcline (feldspar, triclinic form of KAlSi3O8). An exponential distribution of traps gives the best fit to the experimental glow peak. Five TL glow peaks of the Brown microcline which was previously irradiated with γ-rays and then subjected to fading at room temperature are numerically analyzed using the exponential distribution model of traps. The dependence of the best-fit trap parameters are found: (1) the width and the characteristic depth of the trap distribution; (2) the rates of recombination and retrapping of the released electrons from the traps; and (3) the concentration of thermally disconnected traps on the fading time. These trap parameters show a clear dependence on the time of fading. The procedure of the TL analysis using a continuous trap distribution is also reported in detail.

Method of computerized glow curve deconvolution for analysing thermoluminescence

The conventional worldwide accepted method of computerized glow curve deconvolution based on the general order kinetics formalism has two fatal defects in systems where the trapping levels (two or more) have non-zero retrapping probability. The first one is ignoring the thermal connectivity between thermoluminescence (TL) peaks. This arises from the fact that under such a situation electrons trapped at one trapping level, once activated, can be retrapped in another thermally connected level via the conduction band during the recording of the glow curve. The other is the impossibility of obtaining a global minimum, in fitting the experimental TL with the theoretical one with existing techniques.This paper aims to provide answers to these defects. The first one can be overcome by resorting to rigorous analysis using appropriate mathematical rate equations describing the flow of charge carriers. Though the second defect cannot be overcome completely, one can obtain a reasonable fit, which may not be unique. The algorithm is tested for synthetic as well as experimental glow curves.

Origin of the exponential distribution of traps in glass

A recent rigorous analysis of the broad thermoluminescence (TL) peak of a Brown microcline has shown it to be due to an exponential distribution of traps. Incidentally, from the statistical point of view one expects the traps to follow a Gaussian distribution. In order to elucidate the origin of the exponential trap distribution we have analyzed a set of glow peaks of a light green glass recorded under varying conditions of trap filling. The sample upon γ-rays irradiation (dose=7×103 Gy) exhibits a broad TL peak around 191u200a°C. The broad peak becomes narrower once a thermal cleaning technique is applied to the irradiated specimen. Application of computerized glow curve deconvolution reveals that the broad glow curve is due to the presence of a Gaussian distribution of traps. However, in thermally cleaned glow curves the distribution of traps is found to be exponential. This shows that the exponential distribution of traps results from the deeper tail portion of the Gaussian distribution.

The determination of intrinsic trapping parameters of a thermoluminescence peak of BeO

It has been shown that a thermoluminescence (TL) peak of BeO cannot be fitted with a numerically generated glow peak involving only three trapping parameters, namely trap depth, frequency factor and order of kinetics. The peak can be fitted with a TL peak numerically generated by the exact solutions of the basic differential equations. This enables one to determine the five important intrinsic trapping parameters: trap depth, frequency factor, retrapping probability, recombination probability and the concentration of a disconnected trap, an impossible feat under the kinetics formalism.

New method for numerical analysis of thermoluminescence glow curves

An efficient method is proposed to analyse numerically thermoluminescence (TL) glow curves. The new method reduces the number of variable parameters in the rate equations by applying integral calculus to glow curves available for the analysis, a boundary condition, and a maximum condition. This allows for the determination of the best-fit values for all trap parameters, based on a three-level model, when a single pure TL glow curve is given.

Thermally stimulated exoelectron emission from silicon subjected to argon plasma treatment

We have investigated the thermally stimulated exoelectron emission (TSEE) from Ar plasma‐treated Si by x‐ray photoelectron spectroscopy and by employing a theoretical equation. The sample surfaces were exposed to ambient air after the plasma treatment. The TSEE glow curve (298–623 K) exhibited broad emission peaks at ∼373 and ∼473 K, and an increase in the intensity above 573 K. A theoretical analysis revealed that the glow curves were composed of four peaks except for the increase above 573 K, where each peak had a different trap depth, but almost the same electron affinity. The resolved two peaks in the lower temperature region increased compared to those in the higher temperature region with an increase in the O1s/Si2p ratio and also in the Si2p (oxide)/Si2p (substrate) ratio. The relationship of the surface chemical structure to the resolved four peaks is considered.

Simultaneous analysis of the glow curves of thermoluminescence and thermally stimulated exo-electron emission

A new method to analyse the glow curves of thermoluminescence (TL) and thermally stimulated exo-electron emission (TSEE) simultaneously is proposed. The method is based on a model consisting of one trap-one recombination centre for TL and thermionic emission for TSEE. A set of coupled differential equations, describing the charge flow, is numerically solved without any approximation, using the integrated experimental glow curves, maximum conditions and boundary conditions of TL and TSEE. The computer simulation is carried out in the two following cases: the case of correlation between TL and TSEE; and the case of no correlation between TL and TSEE.

Spectral analysis of thermally stimulated exoelectron emission from glass deposited on metal by argon plasma treatment

Abstract Glow curves of thermally stimulated exoelectron emission (TSEE) originating from silicon oxide deposited on Au surfaces by argon plasma treatment are spectrally analyzed. The analysis shows that the variation of the TSEE glow curves due to the conditions of the plasma is ascribed to the growth of the deposited layer.

Thermoluminescence of magnesium aluminum spinel

Abstract Three-dimensional thermoluminescence (TL) spectra of MgAl2O4 spinel exposed to UV light showed a TL peak with a 710nm emission band at 472K and another peak with 520nm around 490K. The algorithm of the numerical analysis based on the model of 2 recombination centers had been developed for TL glow curves of MgAl2O4. The best-fit activation energy and frequency factor were determined as 0.61 eV and 3.75 × 104s−1, respectively, with the chi squared value of 0.010073. On the contrary, the parameters fitted by the conventional theory were the activation energy of 0.66 eV and the frequency factor of 1.25 × 105s−1 with the chi squared value of 0.01358. For TL of MgAl2O4, the model of 2 recombination centers gave a better fit than the conventional theory.