Accepted Manuscript

Kinetic analysis of high temperature secondary thermoluminescence glow peaks in α-Al2O3:C

M.L. Chithambo , C. Seneza , F.O. Ogundare

PII: S1350-4487(14)00120-6

DOI: 10.1016/j.radmeas.2014.04.025

Reference: RM 5226

To appear in: Radiation Measurements

Received Date: 13 December 2013

Revised Date: 29 April 2014

Accepted Date: 30 April 2014

Please cite this article as: Chithambo, M.L., Seneza, C., Ogundare, F.O., Kinetic analysis of hightemperature secondary thermoluminescence glow peaks in α-Al2O3:C, Radiation Measurements (2014),doi: 10.1016/j.radmeas.2014.04.025.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service toour customers we are providing this early version of the manuscript. The manuscript will undergocopyediting, typesetting, and review of the resulting proof before it is published in its final form. Pleasenote that during the production process errors may be discovered which could affect the content, and alllegal disclaimers that apply to the journal pertain.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Kinetic analysis of high temperature secondary

thermoluminescence glow peaks in α-Al2O3:C

M.L. Chithamboa1, C. Senezaa, F.O. Ogundareb

Department of Physics and Electronics, Rhodes University, P O BOX 94, Grahamstown 6140, South Africa

bDepartment of Physics, University of Ibadan, Ibadan, Nigeria

Abstract

The kinetic analysis of secondary glow peaks in carbon-doped aluminium oxide is reported. A glow

curve measured at 0.4oC s-1 after beta irradiation to 3 Gy revealed at least five peaks as a result of

various techniques of glow curve resolution; the dominant peak at 156oC (peak II) and two weaker-

intensity secondary peaks one at 36oC (peak I) and the other at 264oC(peak III). Peaks IIA and IV at

170 and 422oC respectively only became apparent after removal of preceding more prominent peaks.

The secondary peaks are particularly weak in intensity and are as usual dominated by the main

dosimetry peak. The analysis in this report focusses on peak III, usually seen adjacent to the main

dosimetry peak but whose presence is masked by the extreme sensitivity of the latter.

Complementary analyses of the weaker intensity peaks I, IIA and IV are included. Peaks I, IIA and

III are subject to first-order kinetics while for peaks II and IV the issue is less conclusive. The

activation energy increases from 0.72 eV for peak I to about 1.3 eV for peak IV with values for peak

II and IIA similar at ~1 eV. In general, the frequency factor corresponding to the lower temperature

peaks (I, II, and IIA) have values (1010-1012 s-1) that are an order of magnitude or so greater than for

peaks III and IV (109-1011 s-1). Except for peak I, peak II and all other secondary peaks are affected

by thermal quenching whose activation energy was determined as using peak

IIA and as using peak III. The overall conclusion is that all peaks correspond

to electron traps and are associated with the same recombination centre.

Keywords: Thermoluminescence; kinetic analysis; aluminium oxide; thermal quenching

PACS: 78.60.Kn

1 Corresponding author. Tel.: +27 46 603 8450, fax: +27 46 603 8757

Email address: m.chithambo@ru.ac.za (M.L. Chithambo)

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

2

1. Introduction

Carbon-doped aluminium oxide (α-Al2O3:C) is a ultra-sensitive luminescence dosimeter whose

extreme sensitivity is attributed to large concentrations of oxygen vacancies, F and F+ centres,

induced in the material during its synthesis (McKeever et al., 1995; Yukihara and McKeever, 2011).

These and possibly other types of electron centres act as luminescence sites for electrons thermally

or optically released from electron-trapping point defects. The electrons in question are produced as

a result of ionization in previously irradiated materials. In particular, α-Al 2O3:C shows two notable

emission bands, one centred at 420 nm (McKeever et al., 1995) and the other near 330 nm (Vincellér

et al., 2002; Yukihara et al., 2006). The thermoluminescence emitted at 420 nm is attributed to

relaxation of an F centre following electron capture whereas the emission near 330 nm is ascribed to

a similar process but involving hole capture at an F centre (McKeever et al., 1995; Yukihara et al.,

2011). These two mentioned emission bands are by no means exhaustive and other possibilities have

been discussed by McKeever et al., (1995) and by Yukihara and McKeever (2011).

The thermoluminescence glow curve of α-Al2O3:C typically consists of a dominant main peak used

in dosimetry and a number of secondary peaks (Chithambo, 2004 ; Chithambo and Seneza, 2013;

Kortov et al., 2006; Mishra et al., 2007). Luminescence in α-Al 2O3:C is discussed in terms of the

traps responsible for these peaks as well as with reference to deep electron and hole traps that only

compete for charge and do not participate directly in the luminescence process (Chithambo, 2004;

McKeever et al., 1995; Yukihara et al., 2011). Studies of thermoluminescence in α-Al2O3:C have to

date been mainly concerned with the main peak with few exceptions addressing the

thermoluminescence of secondary peaks e.g. (Chithambo, 2004; Chithambo and Seneza, 2013;

Kortov et al., 2006; Mishra et al, 2007).

In this study, a glow curve measured from a sample of α-Al2O3:C at 0.4oC s-1 following beta

irradiation to 3 Gy revealed four subsidiary peaks labelled for ease of reference as I, IIA, III and IV

as will be clarified in due course. This report is mainly concerned with kinetic analysis of peak III,

the one that typically appears immediately after the main peak but for which reports on its kinetic

analysis are meager. This information is complemented by analysis of peaks I, IIA and IV.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

3

2. Experimental details

Samples consisted of α-Al 2O3:C discs of 5 mm diameter and 1 mm thickness (Rexon TLD

Systems, Ohio, USA). Samples were only annealed once at 900oC for 15 minutes to remove

any remanent charge from deep traps prior to use. Thermoluminescence was measured using

a RISØ TL/OSL DA-20 Luminescence Reader. The luminescence was detected by an EMI

9235QB photomultiplier tube through a 7 mm Hoya U-340 filter (transmission band 250 –

390 nm FWHM). Samples were irradiated at ambient temperature using a 90Sr/90Y source

at a nominal dose rate of 0.1028 Gy s-1. All measurements were carried out in a nitrogen

atmosphere to prevent spurious signals from air, to improve thermal contact between sample

holder and heater plate and, together with thermally conductive vacuum grease, to anchor the

sample to the holder and thus aid address any thermal gradient across the sample. Unless

otherwise stated, samples were heated at 0.4 oC s-1 from 30 to 500oC after irradiation to 3 Gy.

The slow heating rate was chosen to ameliorate against the effect of thermal quenching; that

is, incidences of non-radiative recombination, on the already inherently weak intensity

secondary peaks at high temperature.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

4

3. Results and Discussion

3.1 Glow curve structure

Figure 1 shows a glow curve measured from a sample of α-Al2O3:C from 30 to 500oC at

0.4oC s-1 following irradiation to 3 Gy. The glow curve shows three obvious peaks; the

dominant peak at 156oC (peak II) and two weaker-intensity secondary peaks, one at 36oC

(peak I) and the other at 268oC (peak III). Peak I is affected by phosphorescence on its rising

edge (see also Chithambo and Seneza, 2013). As can be deduced by inspection in Fig. 1,

peak II is closely collocated with an as yet undefined peak on its higher temperature side.

This report is mainly concerned with thermoluminescence kinetics of peak III but is

augmented by some observations of the other secondary peaks.

In an attempt to obtain a properly resolved peak III, an irradiated sample was partially heated

to 200oC to remove the two preceding peaks. The outcome of this thermal cleaning

procedure is shown in Fig. 2. The partial heating to 200 not only revealed a distinct peak

III at 264oC but also a previously disguised peak (labelled IIA) at 170oC. The latter is the

possible collocate of the main peak mentioned earlier. It should be noted here that preheating

to temperatures above 156oC (the position of peak II) but below 200oC could not completely

remove the main peak (II). This was only accomplished by heating to 200oC but this heating

also then possibly reduced the intensity of peak IIA. As a matter of interest, it should be

noted that the removal of peak II was abrupt, that is, there was no preheat temperature for

which both peaks appeared simultaneously.

When the sample was irradiated afresh and instead preheated to 265oC to remove peaks I

through IIA, a new secondary glow peak at 422oC (peak IV) became apparent. This is shown

in Fig. 3. The set of peaks IIA, III and IV, being at high temperature, are expectedly subject

to very low luminescence efficiency as has also been remarked at by McKeever et al., (1995).

That this may be the case is reflected in the successively decreasing intensity of the peaks

with the data for peak III and IV particularly noisy.

3.2 Establishing the order of kinetics of peak III

The − stop method was used to assess the order of kinetics for peak III. An irradiated

sample was partially heated in turn to various stop temperatures from 225 up to 265oC in

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

5

steps of 5oC. The position of peak III corresponding to each stop temperature was noted each

time. The set of measurements was made three times. Figure 4 shows against

where it is evident that is essentially independent of . In this case, the partial

heating to stop temperatures changed the initial concentration of trapped charge. Since the

position of peak III was not affected by this change, the result implies that peak III follows

first-order kinetics. A previous study drew the same conclusion but based on the fact that

was independent of dose (Chithambo, 2004).

Only peak III, the main concern of this report, was studied as described. Regarding the other

peaks, a number of studies e.g. (Chithambo and Seneza, 2013; Mishra et al., 2007; Kortov et

al, 2006) show that peak I follows first order kinetics. The order of kinetics of the main peak

(peak II here) has been studied widely with conclusions varying from apparent first order

(McKeever et al., 1995); second order (Kortov et al., 1994) and an ‘academic’ ~1.42 order of

kinetics (Kitis et al., 1994). The order of kinetics of peaks IIA and IV were assessed using an

alternative method to be described later.

3.3 Kinetic analysis

Five different methods consisting of the variable heating rate, peak-shape, whole glow peak,

isothermal analysis and glow curve deconvolution, reviewed elsewhere e.g. Pagonis et al.,

2006, were used to analyse peak III and other secondary peaks for kinetic parameters where

appropriate.

3.3.1 Variable heating rate method

The functional relationship between the peak position and its corresponding heating rate

where is the activation energy and , Boltzmann’s constant, was used first to analyse peak

III. Five sets of measurement were made on a sample irradiated to 3 Gy using heating rates

from 0.2 to 6oC s-1 with peak III isolated by preheating to 200oC as explained earlier. The

resultant plot of Eq. (1) is shown in Fig. 5 from which . The frequency

factor s, was estimated on the basis of first-order kinetics using the expression

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

6

, (2)

as s-1, a value consistent with the frequency with which a bound electron

attempts to escape its binding potential.

3.3.2 Peak-shape method

The activation energy for peak III was also estimated using the shape method as

where for a given peak can be any of the full width at half-maximum (); the lower half-

width ( ) or the upper half-width (). Glow curves analysed in this manner gave average

values of =1.15 ± 0.12 eV, =1.16 ± 0.07 eV and =1.14 ± 0.15 eV. These values,

although necessarily affected by subjectivity in determining , are consistent. In

this case, the frequency factor was s-1 in all three cases.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

7

3.3.3 Whole peak method

The whole glow peak method, another of the techniques used, is in essence the fact that the

area n under a peak subject to order of kinetics b is related to temperature as

(4)

where is the corresponding pre-exponential factor for general-order kinetics (in cm3(b-1)s-1)

and represents the experimental intensities corresponding to measurement temperature

(Pagonis et al., 2006). The technique was applied on an isolated peak III with the value of b

varied to achieve a linear form as expressed in Eq. (4). Figure 6 shows several alternatives of

a semi-logarithmic plot of against for some options of b. The best option

was for which and s-1 respectively.

The values of trapping parameters evaluated using the whole peak method are thus consistent

with values from the peak shape method.

3.3.4 Glow curve deconvolution

The kinetic analysis was complemented by use of glow curve deconvolution (GCD) where

the temperature dependence of the thermoluminescence intensity is described for

general order kinetics as

where is the peak maximum, the corresponding peak position, ,

, and (Kitis et al., 1998). In this method, the desired

values of E and b are the ones that produce the best match between data and model following

iteration.

On the basis of preparatory measurements shown in Figs. 1, 2 and 3, a glow curve from the

sample used in this study should expectedly be properly described by a sum of five

components of Eq. (5). Following initial trials using fits with various components, the most

satisfactory overall fit was obtained with five components. The decision that the fit was good

enough was based on two parameters, the Figure of Merit (FOM),

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

8

where and correspond to the experimental data and values from the fitting function

respectively (Pagonis et al., 2006) and the so-called acceptability-parameter

where is the order of kinetics and (Kitis, 2001). For a good fit, the strictures

for FOM and are 3.5% and 0.4 respectively. Once found, the best estimates for for each

peak were then used to generate the individual peaks and the outcome is shown in Fig. 7 as a

set of five peaks. It should be noted that some techniques of peak resolution, for example, the

− stop method when applied across the temperature range of the whole glow curve imply

that α-Al 2O3:C has three peaks despite a judicious choice of the interval e.g. see

Zahedifar et al. (2012); their Fig. 1 (b). Although some other studies e.g. (Yazici et al., 2003)

propose that the main peak is composed of multiple peaks, it was not the aim of this study to

experimentally reproduce all such putative components. We stress here that the main utility

of this exercise was to show the glow curve in this study as being composed of five peaks

rather than to only obtain kinetic parameters owing to some limitations explained below.

In terms of abstracting the activation energy, although values obtained for the various peaks

were distinct, only the one for peak II at eV (with and

cm3(b-1)s-1) was deemed acceptable (it was found that FOM = 5.5% overall;

and < 0.4 for each peak). The problems here are that in a typical glow curve, peak I is

affected by phosphorescence on its rising edge (see Fig. 1) and so it is geometrically

incomplete in shape; peak IIA is masked by peak II; and peaks III and IV are indeterminate

owing to poor intensity. These factors cause the five-term fit to produce parameters with

meaninglessly large uncertainties for peaks I, IIA, III and IV and cause the FOM to increase

above the 3.5% threshold. It is important to stress here that the poor intensity of the

secondary peaks and hence the large fitting uncertainties is not a consequence of the

experimental or fitting method. The secondary peaks are inherently weak in intensity. The

problem cannot simply be solved by increasing the dose as some might assume as such a step

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

9

does not affect the relative proportions of the peak intensities; the glow curve is still

dominated by peak II and more so when dose is increased.

As explained earlier, glow curves were measured alternatively in two different ways. Firstly,

a sample irradiated to 3 Gy was partially heated to 200 before measurement of the complete

glow curve to reveal peaks IIA, III and IV (Fig. 7, inset a; Fig.2). In the second method, the

sample was thermally cleaned to 265 to leave only peaks III and IV (Fig. 7, inset b; Fig. 3).

Thus Fig. 7 (inset a) shows peaks IIA and III clearer than it does peak IV whereas in Fig. 7

(inset b) peak IV is perceptible. The solid line through data points in Fig. 7 (inset a) is the

best fit of a sum of three components of Eq. (5). Here, the only statistically meaningful

resultant values of and were eV, for peak IIA and

eV, for peak III. In both cases, s-1.

Figure 7 (inset b) shows the glow curve consisting only of peaks III and IV. The solid line is

a sum of two components of Eq. (5) which gave eV, for

peak III and eV, for peak IV. This set of results agrees

broadly with those from Fig. 7 (inset a) for peak III although the precision is affected by the

noisy nature of the data in Fig. 7 (inset b).

Although Eq. (5) has been used to separate glow-peaks, it does not account for any

interaction between the trapping centres. This more expansive problem may possibly be

addressed using a detailed kinetics model using methods discussed, for example, by Sunta et

al., (1994), Nikiforov et al., (2001) or by Chen and Pagonis (2011).

3.3.5 Thermal quenching

The secondary peaks IIA, III and IV occur in a region where thermal quenching should be

much of an effect and that much was commented on by McKeever et al., (1995) but with

reference to peak III. That this is the case can be seen from the effect of heating rate on

thermoluminescence intensity as shown in Fig. 8 where glow curves measured at various

heating rates from 0.6 to 6oC s-1 are compared (with the intensity in units of counts oC-1). As

evident, the area underneath the glow curves, as does the TL intensity (inset, in arbitrary

intensity units), decreases significantly with heating rate in a behaviour indicative of thermal

quenching, that is, increasing incidences of non-radiative recombination as the heating rate is

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

10

increased. Studies of thermal quenching in α-Al 2O3:C have tended to be concerned with only

its effect on the main peak rather than on the secondary ones. We studied the thermal

quenching with respect to peak III and peak IIA.

If, in a set of glow curves measured at different heating rates, the thermoluminescence

measured at the lowest heating rate is assumed to experience the least amount of quenching,

then the area of its glow peak is related, after approximations, to the subsequent quenched

ones measured at higher heating rates through the expression

where is the activation energy of thermal quenching, is a constant and all other

parameters are as previously defined. The thermal quenching apparent in Fig. 8 for both

peaks IIA and III was quantified by plotting against as shown in Fig.

9. The activation energy of thermal quenching was determined as with

using peak III (Fig. 9a) and and using

data of peak IIA (Fig. 9b). We assume that the value of in both cases corresponds to the

same recombination centre but it is not clear at this stage whether the difference between the

two values is only calculational in origin or represents an actual physical effect. Results from

Eq. (8) are necessarily affected by both the magnitude of the intensities and accuracy with

which is known both of which are critical for the inherently low intensity peaks IIA and

III. For this reason, we conclude that the value is more reliable than

the one calculated from the comparatively weaker intensity peak III.

The values above are similar to ones found using the main dosimetry peak for example

and using thermoluminescence (Ogundare et al.,

2013), and using radioluminescence and photoluminescence

(Kortov et al., 1996) as well as with using time-resolved

photoluminescence spectroscopy (TR-PL) by Akselrod et al., (1998) and 1.045 ± 0.002 eV

using time-resolved luminescence, (Nyirenda, 2012). These results show that the electron

traps responsible for peak III and IIA use the same recombination centre associated with the

main peak (peak II) and confirm, quantitatively that peaks III and IIA are indeed affected by

thermal quenching.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

11

4. Kinetic analysis of peaks I and IIA

For completeness, the kinetic analysis was augmented by studies on peak I and peak IIA.

Our previous investigations on peak I (Chithambo and Seneza, 2013; Chithambo, 2004)

showed that this peak has an activation energy of about 0.7 eV, that it is subject to first order

kinetics and fades between irradiation and measurement with a half-life of about 120 s. The

brief that follows is concerned with isothermal analysis of the same peak.

4.1 Isothermal analysis of peak I

For this experiment, a sample irradiated to 0.5 Gy was heated at 1oC s-1 to 30oC.

Phosphorescence was then measured from the sample for 80 s. The measurements were

made at four other temperatures and repeated four times at each temperature.

4.1.1 Isothermal analysis using first order kinetics

Figure 10 shows the change of phosphorescence intensity as a function of time for peak I.

The luminescence decreases exponentially with time as

where is the decay constant (or probability of thermal stimulation given by

) consistent with first-order kinetics as is attested to in the inset. The

phosphorescence was analysed for the activation energy using the dependence of the thermal

probability on measurement temperature , that is,

where oC in this case and all other symbols have their usual meanings. Figure

11 shows a semi-logarithmic plot of against which gave eV and

s-1 respectively. These values of and are consistent with ones calculated

from the initial rise and variable heating rate methods, namely, eV and

eV respectively (Chithambo and Seneza, 2013).

4.1.2 Isothermal analysis of peak I using general order kinetics

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

12

The phosphorescence was also analysed on the basis of general-order kinetics for which

(11)

where is the order of kinetics and is the corresponding decay constant (Chen and

McKeever, 1997). Evidence of general-order kinetics is analogous to Figure 10 except for

being a linear dependence of on with a slope , say, for a suitable value of . The

slope provides a means to evaluate in an Arrhenius-like plot since

Equation (11) was applied on phosphorescence measured at each temperature from 30

through 34oC and various values of used in search of one that best produced linearity in a

plot of against . The slope was noted each time. The experiment was repeated

five times at each temperature. The best estimate for the order of kinetics from all 25

measurements was determined as , a clear indication that peak I is indeed

subject to first-order kinetics.

The slopes corresponding to each measurement temperature described above were

plotted (after suitable manipulation) as a function of in a semi-logarithmic plot as a way

to calculate the activation energy and the corresponding frequency factor in this case. Figure

12 shows this plot from which eV and s-1. Evidently, this is

somewhat of an overestimate in this case for although it is within the range of values, say,

eV, reported by Chithambo and Seneza (2013) or 0.79 eV by Kortov et al.,

(2006) and 0.85 eV by Mishra et al., (2007) using other methods.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

13

4.2. Analysis of peak IIA

Peak IIA was observed at 170oC after preheating a sample dosed to 3 Gy to 200oC at 0.4oC s-1

to remove peaks I and II (Fig. 2). Without this procedure peak IIA was otherwise collocated

with the dominant peak II (Fig. 1). The trade-off from the partial heating to 200oC was an

isolated although much weaker-intensity peak IIA. Nevertheless, the kinetic parameters for

peak IIA were estimated using the initial rise, variable heating rate and peak shape methods.

Figure 13 shows a plot of against in application of the initial-rise method from

which eV and s-1 using the initial-rise method. A similar plot

but using the variable heating rate method gave eV and s-1.

The TL intensity of peak IIA decreased with heating rate between 0.2 and 6oC s-1 in a manner

consistent with thermal quenching (Fig. 13, inset) with an activation energy

(Fig. 9b). Peak IIA was also analysed for kinetic parameters using the

peak-shape method which gave eV, eV and

eV. The corresponding values of the frequency factor, in s-1,

were , and in that order.

The set of values from the three methods (initial-rise, variable heating rate and peak shape

estimates) compare favourably and are representative of the activation energy and frequency

factor for peak IIA. The geometrical factor , which is related to the order of

kinetics (Chen and McKeever, 1997; McKeever, 1985), was calculated as

suggestive of first order kinetics in agreement with the conclusion from the

glow curve deconvolution method i.e. . Although in principle the peak

shape method should be affected by a change in shape of the peak owing to thermal

quenching and a concomitant decrease in sampling rate due to non-radiative recombination,

this possibility was compensated for by using a particularly slow heating rate of 0.4oC s-1.

Thus values from the peak shape method are as reliable as any from the other methods used

to analyse peak IIA.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

14

5. A brief meta-analysis of kinetic parameters in αααα-Al2O3:C

It is instructive to compare and contrast values of kinetic parameters determined using

different methods in order to find out if there are any patterns, and if so, to try to account for

such trends. This exercise is simply a pragmatic concern because the ease with which

parameters can be found either from curve fitting or application of various methods of

analysis does not necessarily reflect the reliability with which the results ought to be

regarded.

Table 1 is a list of kinetic parameters found in this study and some values from the literature

are included for completeness. The list is not meant to be exhaustive. Our experimental

study showed five peaks which were labelled I, II, IIA, III and IV. The activation energy

scales up from 0.72 eV for peak I to about 1.3 eV for peak IV with values for peak II and IIA

similar at ~1 eV. Thus the deeper the trap, the higher the activation energy as would be

expected. The main peak (peak II) has often been adjudged to be a multiplex of peaks e.g.

(McKeever et al., 1995; Yazici et al., 2003) and the similarity in the value of activation

energy for peaks II and IIA is consistent with this notion.

Peaks I, IIA and III are subject to first-order kinetics while for peaks II and IV the matter is

less conclusive. Although for peak II, is comparable with 1.42 reported by

Kitis et al., (1994), this value probably describes the whole peak including its collocates and

not necessarily one component exclusively. For this reason, this value is only a guide as the

possible order of kinetics for the main peak. As regards peak IV, the range between the

largest and smallest probable values of straddle first and second order kinetics. This

imprecision is probably caused by the scatter in data points of peak IV used in the curve-

fitting.

Across all methods used for each peak in this work, the best estimate of the activation energy

determined using glow curve deconvolution exceeds all else in each set. In view of this, it is

possible that the only value found for peak IV i.e., might be a slight over-

estimate on the real value and should be regarded only as a first estimate.

The frequency factor does not show a systematic dependence on peak position although the

lower temperature peaks (I, II, and IIA) have values (1010-1012 s-1) that are an order of

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

15

magnitude or so greater than for peak III and IV (109-1011 s-1) barring a few outliers. It

should be noted that the value corresponding to peak II, whose , is in units of cm3(b-1)s-1

or indeed in s'⋅n0b-1 and is strictly not constant because it depends on the initial concentration

. In comparison, Kitis (1994) reported a value of 1014 s-1 for peak II whereas Mishra et al.,

(2007) reported s-1. Although, it is to be expected that a deeper trap will empty at a

higher temperature, the relative positions of glow peaks are not influenced by the activation

energy and frequency factor only but also by other factors including the recombination and

retrapping probabilities (McKeever, 1985; Chen and McKeever, 1997; Townsend and Kelly,

1973). Thus combinations of high activation energy and low frequency factor as for peak IV

are possible.

Except for peak I, peak II and all secondary peaks are affected by thermal quenching with an

activation energy of ~ 1 eV and qualitatively so for peak IV. Comparing values of the

activation energy for thermal quenching as listed, it is apparent that the value of ∆E is

generally independent of the method used to determine it.

6. Mechanisms

Previous studies concerned with the main dosimetry peak suggest that the mechanism leading

to emission of thermoluminescence in α-Al2O3:C is the recombination of an electron with an

F+ centre producing an excited F centre. The luminescence is emitted as a result of the

relaxation of the electron from the 3P to the 1S ground state (McKeever et al., 1995; Yukihara

and McKeever, 2011). Apart from evidence from emission spectra (Bøtter-Jensen et al.,

2003; Yukihara et al., 2011), the presence of F+ vacancies as luminescence centres was

demonstrated by positron annihilation with a lifetime of 359 ps in γ-irradiated α-Al2O3:C

(Chithambo et al., 2002).

The results observed in this report may be explained with reference to the energy band

diagram shown in Fig. 14(a) based on models by Yukihara et al., (2003), Vincellér et al.,

(2002), Chithambo (2004) and Pagonis et al., (2013) but with minor modifications to account

for present findings. Electrons are transferred to the conduction band by ionization

(transition 1). The free electrons may then be captured (downward arrows) at the shallow

trap (ST), main electron trap (MT) or intermediate energy traps (T-IIA, T-III, T-IV)

associated with peaks I, II, IIA, III, IV respectively. The electrons can also be captured at

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

16

deep electron-traps (DT) and at deep hole-traps (HT). The deep traps are not directly

involved in the luminescence emission and primarily only compete for charge. The localised

energy levels shown in Fig. 14(a) are by no means exhaustive and exclude the F+ centre

associated with emission in the ultra-violet spectral region as well as other possible

components of peak II described elsewhere e.g. (Dallas et al., 2008; Zahedifar et al., 2012).

It is known that at low dose, say well below 10 Gy (Chithambo, 2004), the rate of production

of F+ centres by capture of holes at F centres and their conversion to F centres by electron-

capture is approximately equal and competition for electrons from the deep electron- and

hole-traps in this low-dose regime is irrelevant. Thus the intensity of TL is directly correlated

with concentration of trapped charge at electron traps. Studies concerned with fading in peak

I show that the loss of electrons at ambient temperature due to phosphorescence from peak I

is accompanied by a concomitant increase in the TL intensity from peaks II and III

(Chithambo and Seneza, 2013). This feature implies that the latter traps successfully

compete for charge from the unstable peak I. Interestingly, the rate of change of the TL

intensity for peaks II and III are identical. We surmise then that the electron traps responsible

for peaks II and III (and possibly IIA and IV) act as competitor traps in confirmation of

earlier proposals (Chithambo et al., 2002; Chithambo, 2004). We also presume that owing to

a number of reasons including low electron capture probability, electron trapping is less

efficient at the high temperature secondary traps compared with that at the primary trap

responsible for peak II, the latter being responsible for capture of most charge during

irradiation. It is also likely that both peak IIA and peak III are associated with the same

recombination centre as for peak II given the similarity in the value of ∆E abstracted from

these two peaks with that known from analysis of peak II. It should be noted that thermal

quenching can equally be explained with reference to the configurational coordinate model

shown in Fig. 14(b) where an electron in the excited state can decay non-radiatively to the

ground state via the emission of phonons of quanta (Bøtter-Jensen et al., 2003). On this

basis, the difference between the value of as found from peaks IIA and III could reflect a

shifting of energy levels since thermal quenching is a temperature-induced effect. This

proposition however requires further examination.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

17

7. Conclusion

The enduring interest in carbon-doped aluminium oxide has mainly to do with its peculiarly

intense main thermoluminescence peak utilized in dosimetry applications using various

modes of stimulated luminescence. Apart from this peak, the material has some unstable

electron traps whose presence is revealed as thermoluminescence at temperatures close to

ambient as well as other weak intensity peaks that are masked by the main peak but

nevertheless are present at relatively higher temperatures. In this study, the kinetic analysis

of secondary glow peaks in carbon-doped aluminium oxide has been reported. A glow curve

measured at 0.4oC s-1 after beta irradiation to 3 Gy showed at least five peaks following

various methods of glow curve resolution. These were the dominant peak at 156oC (peak II)

and weaker-intensity secondary peaks at 36oC (peak I), peak IIA at 170oC, peak III at 264oC

and peak IV at 422oC. The activation energy of the peaks increases from 0.72 eV for peak I

to about 1.3 eV for peak IV with values for peak II and IIA similar at ~1 eV. The

luminescence intensity of peaks III and IV decrease with heating rate in a manner consistent

with thermal quenching. The values of the activation energy for thermal quenching found in

each case are similar to ones often quoted for the main peak implying that these peaks are

associated with the same recombination centre.

Acknowledgements The authors acknowledge with gratitude financial assistance from Rhodes University, the

National Research Foundation of South Africa and the Government of Rwanda.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

18

References

Akselrod, M. S., Larsen, N. A., Whitley, V., McKeever, S. W. S., 1998. Thermal quenching

of F-center luminescence in Al2O3:C. J. Appl. Phys. 84, 3364-3373.

Bøtter-Jensen, L., McKeever, S.W.S., Wintle, A.G., 2003. Optically Stimulated

Luminescence Dosimetry, Elsevier, Amsterdam.

Chen, R., McKeever, S.W.S., 1997. Theory of thermoluminescence and Related Phenomena

World Scientific, Singapore.

Chen, R., Pagonis, V., 2011. Thermally and optically stimulated luminescence: a simulation

approach, Wiley, Chichester.

Chithambo, M. L., 2004. Concerning secondary thermoluminescence peaks in α-Al2O3:C.

S. Afric. J. Sci. 100, 524-527.

Chithambo, M.L., Sendezera, E.J., Davidson, A.T., 2002. A preliminary

thermoluminescence and positron annihilation study of α-Al 2O3:C. Radiat. Prot. Dosim. 100,

269 – 272.

Chithambo, M. L., Seneza, C., 2014. Kinetics and dosimetric features of secondary

thermoluminescence in carbon-doped aluminium oxide. Physica B, 439, 165-168.

Dallas, G. I., Afouxenidis, D., Stefanaki, E. C., Tsagas, N. F., Polymeris, G. S., Tsirliganis,

N. C., Kitis, G., 2008. Reconstruction of the thermally quenched glow-curve of Al2O3:C

phys. stat. sol. (a) 205, 1672–1679.

Kitis, G., 2001. TL glow-curve deconvolution functions for various kinetic orders and

continuous trap distribution: Acceptance criteria for E and s values. J. Radioanalyt. and Nucl.

Chem. 247, 697-703.

Kitis, G., 2002. Confirmation of the influence of thermal quenching on the initial rise method

in α-Al 2O3:C. phys. stat. sol. (a) 191, 621-627.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

19

Kitis, G., Papadopoulus, S., Charalambous, S., Tuyn, J. W. N.,1994. The influence of heating

rate on the response and trapping parameters of Alpha-Al2O3:C. Radiat. Prot. Dosim. 55, 183-

190.

Kitis, G., Gomez-Ros, J.M., Tuyn, J.W.N., 1998. Thermoluminescence glow-curve

deconvolution functions for first, second and general orders of kinetics. J. Phys. D: Appl.

Phys. 31, 2636–2641.

Kortov, V.S., Milman, I.I.,Kirpa, V.I., Lesz, J.,1994. Some features of Alpha-Al2O3

dosimetric thermoluminescent crystals. Radiat. Prot. Dosim. 55, 279-283.

Kortov, V.S., Milman, I.I., Kirpa, V.I., Lesz, J., 1996. Thermal quenching of TL in Alpha-

Al2O3 dosimetric crystals. Radiat. Prot. Dosim. 65, 255-258.

Kortov, V. S., Nikiforov, S.V., Sadykova, E.Z., 2006. Competing processes with participation

of shallow traps in an anion-defective aluminum oxide. Russ. Phys. J. 49- 221-224.

McKeever, S.W.S., 1985. Thermoluminescence of Solids, Cambridge University Press,

Cambridge.

McKeever, S. W. S., Moscovitch, M., Townsend, P.D., 1995. Thermoluminescence

dosimetry materials: properties and uses. Nuclear Technology Publishing, Kent.

Mishra, D.R., Kulkarni, M.S., Muthe, K.P., Thianahara, C., Roy, M., Kulshreshtha, S.K.,

Kannan, S., Bhatt, B.C., Gupta, S.K., Sharma, D.N., 2007. Luminescence properties of α-

Al2O3:C with intense low temperature TL peak. Radiat. Meas. 42, 170–176.

Nikiforov, S.V., Milman, I.I., Kortov, V.S., 2001. Thermal and optical ionization of F-

centers in the luminescence mechanism of anion-defective corundum crystals. Radiat. Meas.

33, 547-551.

Nyirenda. A., 2012. Mechanisms of luminescence in α-Al2O3: C: Investigations using time-

resolved optical stimulation and thermoluminescence techniques. Unpublished MSc thesis.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

20

Ogundare, F. O., Ogundele, S. A., Chithambo, M. L., Fasasi, M. K., 2013.

Thermoluminescence characteristics of the main glow peak in α-Al 2O3:C exposed to low

environmental-like radiation doses. J. Lumin. 139, 143-146.

Pagonis, V., Ankjærgaard C., Jain M, Chen, R., 2013. Thermal dependence of time-resolved

blue light stimulated luminescence in α-Al2O3:C. J. Lumin. 136, 270–277.

Pagonis, V., Kitis, G., Furetta, C., 2006. Numerical and Practical Exercises in

Thermoluminescence. Springer, Berlin.

Sunta, C.M., Yoshimura, E.M., Okuno, E., 1994. Interactive kinetics in thermoluminescence

(TL) and its effect on glow curves and their growth as a function of dose. Phys. Status Solidi,

186, 199-208.

Townsend P.D., Kelly J.C.,1973. Defects in Semiconductors and Insulators. Chatto and

Windus.

Vinceller S., Molnar G., Berkane-Krachai A., Iacconi P., 2002. Influence of thermal

quenching on the thermostimulated processes in α-Al2O3. Role of F and F+ centres. Radiat.

Prot. Dosim. 100, 79-82.

Yazici, A. N., Solak, S., Ozturk, Z., Topaksu, M., Yegingil, Z., 2003. The analysis of

dosimetric thermoluminescent glow peak of α-Al2O3:C after different dose levels by β-

irradiation J. Phys. D: Appl. Phys. 36, 181-191.

Yukihara, E.G., McKeever, S.W.S., 2011. Optically stimulated luminescence: Fundamentals

and Applications, Wiley, New York.

Yukihara, E.G., McKeever, S.W.S., 2006. Ionisation density dependence of the optically and

thermally stimulated luminescence from α-Al2O3. Radiat. Prot. Dosim. 119, 206-217.

Yukihara, E. G., Whitley, V. H., Polf, J. C., Klein, D. M., McKeever, S. W. S., Akselrod, A.

E., Akselrod, M .S., 2003. The effects of deep trap population on the thermoluminescence of

Al2O3:C. Radiat. Meas. 37, 627-638.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

21

Zahedifar, M., Eshraghi, L., Sadeghi, E., 2012. Thermoluminescence kinetics analysis of α-

Al2O3:C at different dose levels and populations of trapping states and a model for its dose

response Radiat. Meas. 47, 957-964.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

22

Figure and table captions

Figure 1 A glow curve of α-Al2O3:C measured at 0.4oC s-1 from a sample irradiated to 3 Gy.

Figure 2 The glow curve measured at 0.4oC s-1 after preheating to 200oC (using a correctly

calibrated sample heater) after a dose of 3 Gy. The procedure revealed peaks IIA and III.

Figure 3 A glow curve measured at 0.4oC s-1 from 30oC after preheating to 265oC following a

dose of 3 Gy. The partial heating revealed peak IV at 422oC in addition to peak III.

Figure 4 A plot of against used to assess the order of kinetics for peak III. Each

data point is an average of three and the margin of error in is simply the standard

deviation of the set. The dotted line is only a visual guide.

Figure 5 The variable heating rate method applied on peak III. Each data point is an average

of five with the uncertainty determined as the standard deviation in the set.

Figure 6 A plot of versus for different values of order of kinetics .

Figure 7 A glow curve measured at 0.4oC s-1 following irradiation to 3 Gy (solid circles).

The five separate peaks obtained using deconvolution (dashed and dotted lines) are shown for

completeness. The insets show glow curves, after correction for background, measured after

partial heating to 200 and 265 (a) and (b) respectively, fitted with two components of Eq.

(5).

Figure 8 A comparison of glow curves measured at different heating rates. The inset shows the change of intensity (in arbitrary units; normalised) against heating rate for peak III.

Figure 9 A plot of against for peak III used to evaluate the

parameters for thermal quenching.

Figure 10 Phosphorescence from peak I and in the inset, the same but plotted on a semi-

logarithmic plot to confirm its kinetics as first order .

Figure 11 A graph of against used to find the activation energy for peak I.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

23

Figure 12 A graph of against used to find the activation energy for peak I on

the basis of general order kinetics.

Figure 13 Application of the initial rise method on peak I. The inset shows the change of

TL intensity (normalized) with heating rate for peak IIA.

Figure 14 An energy-band model showing the shallow trap (ST), intermediate energy traps

(T-IIA, T-III, T-IV) and the primary trap (MT) responsible for peaks I, IIA, III, IV and II

respectively. Levels DT and HT denote deep electron- and hole-traps whereas transition 1

denotes ionization. Radiative emission is shown by transition 2 and non-radiative

recombinations (transition 3) are possible if an electron in the 3P level can overcome the

energy barrier ∆E as shown.

Table 1 Kinetic parameters determined using various methods. The indices a, b, c

corresponding to the peak shape method stand for , and respectively. The

geometrical factor for peak IIA was , and in case of general order kinetics,

the units for are in cm3(b-1) s-1 unless otherwise stated.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

24

Figure 1

Temperature (oC)

0 100 200 300 400 500 600

TL

inte

nsity

(a

.u)

1e+2

1e+3

1e+4

1e+5

1e+6

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

25

Figure 2

Temperature (oC)

20 100 180 260 340 420 500

TL

inte

nsity

(a

.u)

0

500

1000

1500

2000

III

IIA

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

26

Figure 3

Temperature (oC)

20 100 180 260 340 420 500

TL

inte

sity

(a.

u)

200

300

400

500

600

700

III

IV

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

27

Figure 4

Tstop (oC)

210 220 230 240 250 260 270

Tm

(o C

)

250

254

258

262

266

270

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

28

Figure 5

1/kTm (eV)-1

19.6 20.0 20.4 20.8 21.2 21.6 22.0 22.4

ln (

Tm

2 /β)

10.8

11.4

12.0

12.6

13.2

13.8

14.4

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

29

Figure 6

1/kT (eV)-1

20 21 22 23

ln (

I(T

)/nb

)

-10

-8

-6

-4

-2

0

b = 0.9b = 1.0b = 1.1b = 1.2

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

30

Figure 7

Temperature (K)

300 400 500 600 700 800 900

TL

inte

nsi

ty (

a.u

)

0

2e+5

4e+5

6e+5

8e+5

1e+6

II

IIAIII

IV

I

0

400

800

1200

1600

IIA III

IV

300 400 500 600 700 800

0

100

200

300

400

IV

IIIIV

(a)

(b)

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

31

Figure 8

Temperature (oC)

0 100 200 300 400 500 600

TL

inte

nsity

(co

unts

o C-1

)

0

200

400

600

800

1000

0.60.8124 Heating rate (oC s-1)

0 1 2 3 4 5 6

Inte

nsity

(a.

u)

0.0

0.4

0.8

1.2

oC s-1

IIA

III

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

32

Figure 9

1/kTm (eV)-1

19.5 20.0 20.5 21.0 21.5 22.0

ln [(

I A/I

Q)-

1]

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

(a)

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

33

1/kTm (eV)-1

23 24 25 26

ln [(

I A/I

Q)-

1]

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

(b)

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

34

Figure 10

Time (s)

0 20 40 60 80 100

Inte

nsi

ty (

a.u

)

0

50

100

150

200

250

Time (s)

0 20 40 60 80

ln(I

/Io)

-4

-3

-2

-1

0

1

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

35

Figure 11

1/kT (eV)-1

37.8 38.0 38.2 38.4

ln p

-3.6

-3.5

-3.4

-3.3

-3.2

-3.1

-3.0

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

36

Figure 12

1/kT (eV)-1

37.8 38.0 38.2 38.4

ln m

-6.4

-6.3

-6.2

-6.1

-6.0

-5.9

-5.8

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

37

Figure 13

1/kT (eV)-1

27.6 27.8 28.0 28.2 28.4 28.6 28.8

ln I

6.4

6.6

6.8

7.0

7.2

7.4

Heating rate (oC s-1)

0 1 2 3 4 5 6 7

Inte

nsity

(a

.u)

0.0

0.4

0.8

1.2

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

38

Figure 14

(a)

(b)

Configurational Coordinate, Q

Ene

rgy, E

Ground stateExcited state

∆E

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

39

Peak Method Dose (Gy E (eV) b s (s-1

) ∆E (eV) C Reference

IV GCD 3 1.25 ± 0.27 1.48 ± 0.52 1.4 x 107 Fig.7,inset b

III Tm-Tstop 3 1 Fig. 4

Tm-dose 1 Chithambo (2004)

Var. heat rate 3 1.51 ± 0.06 6 x 1012 Fig. 5

Peak-shape 3 1.15 ± 0.12a 1 x 109 Sect. 3.3.2

3 1.16 ± 0.07b 1 x 109 Sect. 3.3.2

3 1.14 ± 0.15c 1 x 109 Sect. 3.3.2

Whole peak 3 1.10 ± 0.04 1 x 109 Fig. 6

GCD 3 1.27 ± 0.06 1.00 ± 0.07 1 x 1010 Fig.7,inset a

3 1.27 ± 0.09 1.00 ± 0.11 1 x 1010 Fig.7,inset b

3 1.48 ± 0.10 4.3x 1010 Fig. 9(a)

IIA GCD 3 1.01 ± 0.02 1.20 ± 0.04 1 x 1010 Fig.7,inset a

3 0.95 ± 0.04 2.2x 1010 Fig. 9(b)

Initial rise 3 0.85 ± 0.04 1 x 108 Fig. 13

Var. heat rate 3 0.92 ± 0.08 1 x 1010 Sect. 4.2

Peak shape 3 0.86 ± 0.11a 1† 2.2 x 1010 Sect. 4.2

3 0.84 ± 0.08b 1† 1.2 x 1010 Sect. 4.2

3 0.86 ± 0.20c 1† 1.2 x 1010 Sect. 4.2

II GCD 3 1.19 ± 0.02 1.42 ± 0.15 3.0 x 1012 Sect. 3.3.4

Initial rise\TL 0.0012 1.48 1.08 Kitis (2002)

Initial rise 1 1.33 ± 0.01 Nyirenda (2012)

Time-resolved OSL 1 1.045 ± 0.020 Nyirenda (2012)

Whole curve\TL 0.0048 1.00 ± 0.02 0.96 ± 0.05 Ogundare et al., (2013)

TR-PL 1.08 ± 0.03 Akselrod et al., (1998)

I Phosphorescence 0.5 0.72 ± 0.05 2.6 x 1010 Fig. 11

Phosphorescence 0.5 1.06 ± 0.07 Sect. 4.1.2

Phosphorescence 0.5 0.83 ± 0.06 2.6 x 1012 Fig. 12

Phosphorescence 0.125 0.85\1.07 1 1015

\1016 Mishra et al., (2007)

Initial rise 0.5 0.72 ± 0.01 3.0 x 1010 Chithambo and Seneza (2013)

Var. heat rate 0.5 0.72 ± 0.04 3.0 x 1010 Chithambo and Seneza (2013)

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Peak Method Dose (Gy E (eV) b s (s-1) ∆E (eV) C Reference

IV GCD 3 1.25 ± 0.27 1.48 ± 0.52 1.4 x 107 Fig.7,inset b

III Tm-Tstop 3 1 Fig. 4

Tm-dose 1 Chithambo (2004)

Var. heat rate 3 1.51 ± 0.06 6 x 1012 Fig. 5

Peak-shape 3 1.15 ± 0.12a 1 x 109 Sect. 3.3.2

3 1.16 ± 0.07b 1 x 109 Sect. 3.3.2

3 1.14 ± 0.15c 1 x 109 Sect. 3.3.2

Whole peak 3 1.10 ± 0.04 1 x 109 Fig. 6

GCD 3 1.27 ± 0.06 1.00 ± 0.07 1 x 1010 Fig.7,inset a

3 1.27 ± 0.09 1.00 ± 0.11 1 x 1010 Fig.7,inset b

3 1.48 ± 0.10 4.3x 1010 Fig. 9(a)

IIA GCD 3 1.01 ± 0.02 1.20 ± 0.04 1 x 1010 Fig.7,inset a

3 0.95 ± 0.04 2.2x 1010 Fig. 9(b)

Initial rise 3 0.85 ± 0.04 1 x 108 Fig. 13

Var. heat rate 3 0.92 ± 0.08 1 x 1010 Sect. 4.2

Peak shape 3 0.86 ± 0.11a 1† 2.2 x 1010 Sect. 4.2

3 0.84 ± 0.08b 1† 1.2 x 1010 Sect. 4.2

3 0.86 ± 0.20c 1† 1.2 x 1010 Sect. 4.2

II GCD 3 1.19 ± 0.02 1.42 ± 0.15 3.0 x 1012 Sect. 3.3.4

Initial rise\TL 0.0012 1.48 1.08 Kitis (2002)

Initial rise 1 1.33 ± 0.01 Nyirenda (2012)

TR-OSL 1 1.045 ± 0.020 Nyirenda (2012)

Whole curve\TL 0.0048 1.00 ± 0.02 0.96 ± 0.05 Ogundare et al., (2013)

TR-PL 1.08 ± 0.03 Akselrod et al., (1998)

I Phosphorescence 0.5 0.72 ± 0.05 2.6 x 1010 Fig. 11

Phosphorescence 0.5 1.06 ± 0.07 Sect. 4.1.2

Phosphorescence 0.5 0.83 ± 0.06 2.6 x 1012 Fig. 12

Phosphorescence 0.125 0.85\1.07 1 1015\1016 Mishra et al., (2007)

Initial rise 0.5 0.72 ± 0.01 3.0 x 1010 Chithambo and Seneza (2013)

Var. heat rate 0.5 0.72 ± 0.04 3.0 x 1010 Chithambo and Seneza (2013)

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

●The kinetic analysis of secondary glow peaks in carbon doped aluminium oxide is

reported.

● The activation energy increases from 0.72 eV for peak I to ~1.3 eV for peak IV. For

peaks II, IIA E~1 eV.

●Except for peak I, peak II and all other secondary peaks are affected by thermal

quenching.

● ΔE � 0.95 � 0.04eV using peak IIA and 1.48 � 0.10eV using peak III.