Thermoluminescence of aquamarine: A preliminary study

Thermoluminescence of aquamarine, the cyan variety of beryl (Be3Al2(SiO3)6), is reported. Samples were irradiated at room temperature using a 90Sr/90Y β source at a rate of 0.10 Gys–1 . Measurements made at 1 ◦C/s after irradiation to 10 Gy show a prominent glow peak at 75 ◦C and three secondary peaks at 113, 188 and 306 ◦C.

Radiation Measurements 155 (2022) 106806 Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas Thermoluminescence of aquamarine: A preliminary study Jorge Herrera a, Rafael Cogollo a, *, Omar D Guti´errez b, M.L Chithambo c a Grupo de Materiales y Física Aplicada, Departamento de Física, Universidad de C´ ordoba, Cra # 76-103, Montería, 230002, Colombia Grupo de Química B´ asica, Aplicada y Ambiente, Facultad de Ciencias Exactas y Aplicadas, Instituto Tecnol´ ogico Metropolitano, Calle 73 No 76A – 354, Medellín, 050034, Colombia c Department of Physics and Electronics, Rhodes University, P O Box 94, Grahamstown, 6140, South Africa b A R T I C L E I N F O A B S T R A C T Keywords: Beryl Aquamarine Thermoluminescence Kinetic-analysis Reproducibility Thermoluminescence of aquamarine, the cyan variety of beryl (Be3Al2(SiO3)6), is reported Samples were irra­ diated at room temperature using a 90Sr/90Y β source at a rate of 0.10 Gys–1 Measurements made at ◦ C/s after irradiation to 10 Gy show a prominent glow peak at 75 ◦ C and three secondary peaks at 113, 188 and 306 ◦ C Kinetic analysis of the main peak performed using the initial rise, whole glow peak and curve fitting methods show that the peak follows first order kinetics, that its activation energy is of the order of eV and that it has a frequency factor of ~1012 s− Reproducibility analysis shows that the material reproduces its response under identical experimental conditions with a maximum uncertainty of 2.0% Introduction major dopants whereas in Co, V and Fe-doped samples the luminescence is deduced to be from the host lattice as the emission band is not modified by introduction of dopant as evident from TL and radio­ luminescence spectra (Chithambo et al., 1995) Some reports on the luminescent and dosimetric properties of beryl reported no emission (Kati et al., 2012) In this work the thermoluminescence of the aquamarine variety of beryl is reported Samples were irradiated at room temperature using a90Sr/90Y β source at a rate of 0.10 Gys-1 We use different methods of kinetic analysis to determine the kinetic parameters and to establish the influence of the dose on its TL behavior In addition, one of its dosimetric characteristics, such as reproducibility, is reported Beryl (Be3Al2(SiO3)6) is a ring silicate with a hexagonal crystalline structure Varieties of beryl exhibit a wide range of color including green (for emerald), blue (for aquamarine), pink (for morganite), among others From a dosimetry point of view, beryl is of interest as some of its luminescence features resemble those of quartz (Chithambo et al., 1995) Both are built of framework structures (but not framework sili­ cates) and they also contain silica tetrahedra linked to each other (Chithambo et al., 1995) This report is concerned with aquamarine, the cyan variety of beryl Reports of characterization of beryl by thermoluminescence (TL) are rare Only one report has been published on the thermoluminescence of natural beryl doped with transition metals (Chithambo et al., 1995) That work was the first successful attempt to record the low-temperature spectra of beryl This information is useful for the identification of defect properties The pale blue hue of aquamarine alluded to earlier is ascribed to the presence of Fe-related cations within its matrix By way of comparison, beryl doped with Fe shows strong thermoluminescence emission between 300 and 400 nm (Chithambo et al., 1995) In addition, whereas manganese and chromium dopants are efficient thermolumi­ nescent activators in beryl, the absence of a common feature in the TL spectra of doped beryl shows how intrinsic and extrinsic defects define its TL This is exemplified by the fact that in emerald (Cr doped beryl) and morganite (Mn doped beryl) the luminescence is attributed to the Materials and methods Measurements were made on commercially available aquamarine (African Gems and Minerals Inc., Cape Town, South Africa) The sample, prepared in coarse grain form, was used as received without any premeasurement treatment Experiments were performed using a RISØ TL/OSL DA-20 Luminescence Reader The luminescence was detected by an EMI 9235QB photomultiplier tube through a mm Hoya U-340 filter (transmission band 250–390 nm FWHM) Samples were irradiated at room temperature using a90Sr/90Y β source at a rate of 0.10 Gys-1 All measurements were carried out at a heating rate of 1◦ Cs− * Corresponding author E-mail address: rafaelcogollo@correo.unicordoba.edu.co (R Cogollo) https://doi.org/10.1016/j.radmeas.2022.106806 Received 26 November 2021; Received in revised form 20 May 2022; Accepted 26 May 2022 Available online 29 May 2022 1350-4487/© 2022 Elsevier Ltd All rights reserved J Herrera et al Radiation Measurements 155 (2022) 106806 Fig Glow curve of aquamarine measured at ◦ C/s after irradiation at 8, 40 and 100 Gy of beta dose The inset shows the lower intensity peaks at 188 and 306 ◦ C respectively for the same dose Fig Variation of position of the main peak with irradiation dose The inset shows the influence of irradiation dose on the main peak for glow curves corresponding at 8, 40 and 100 Gy of beta dose Results 3.2 Qualitative assessment of order of kinetics 3.1 Glow curve features 3.2.1 Dependence of peak position on dose The position (TM ) of the main peak is shown in Fig as a function of irradiation dose The position is independent of dose at 74.9 ± 0.8 ◦ C from 0.1 to 100 Gy This result suggests that the main glow peak is consistent with first-order kinetics Some glow curves corresponding to various doses are shown in the inset Fig shows examples of glow curves recorded at ◦ C/s after irra­ diation to different doses (8, 40 and 100 Gy) The main peak is at 75 ◦ C There are three secondary peaks at 113, 188 and 306 ◦ C The lower intensity peaks are shown more clearly in the inset to Fig J Herrera et al Radiation Measurements 155 (2022) 106806 Fig Glow curve of aquamarine after various preheating temperatures All measurements correspond to irradiation to 10 Gy Fig Plots of ln(I) versus 1/kT for the initial rise portion of the main peak of aquamarine corresponding to 8, 40 and 100 Gy beta dose Fig Plots of ln(I/nb) against 1/kT for some values of b for the glow peak recorded after beta irradiation to 100 Gy 3.2.2 Tm-Tstop analysis for the main peak glow curve The order of kinetics of the main peak was determined using the TmTstop method (McKeever and Chen, 1997) In the Tm-Tstop analysis, the position of a peak, Tm is monitored with respect to the preheat tem­ perature, Tstop The position of a first order peak is independent of preheat temperature while that of a non-first order peak shifts towards high temperatures with increase in the preheat temperature In our case, a sample irradiated to 10 Gy was first partially heated to 20 ◦ C and after cooling, the complete glow curve was measured from 20 ◦ C to 400 ◦ C The procedure was repeated on the same sample, freshly irradiated each time, but with the Tstop temperature increased by ◦ C from 20 up to 52 ◦ C Fig shows that the position of the main peak is independent of Tstop at 76.2 ± 0.10 ◦ C showing that the main peak follows first order kinetics The result is consistent with the one on the dependence of Tm on dose 3.3 Kinetic analysis The kinetic analysis of the main peak was determined using the initial rise (IR), peak shape (PS), whole glow peak (WGP), curve fitting (CF) and variable heating rate (VHR) methods described elsewhere (Pagonis et al., 2006) 3.3.1 Initial rise method The activation energy was determined using the initial rise method for measurements corresponding to irradiation to 8, 40 and 100 Gy Fig shows plots of ln(I) versus 1/kT for the initial rise portion of the main peak recorded after irradiation at 8, 40 and 100 Gy The values of J Herrera et al Radiation Measurements 155 (2022) 106806 area n under a glow peak is related to the order of kinetics b as (Pagonis et al., 2006): ( ) ′ I s E (1) ln b = ln − n β kT where s´is the effective frequency factor, β is the heating rate and E, the activation energy For an appropriate value of b, the term ln(I /nb ) is a linear function of 1/kT with a slope − E and an intercept equal to ln(s´/β) Fig shows a plot of ln(I /nb ) against 1/kT for some value of b for the glow peak recorded after irradiation to 100 Gy The plot for which b = 1.1 is linear The values of the activation energy and frequency factor are 0.92 ± 0.01 eV and 3.7 × 1011 s− 1respectively, typical of this parameter The values of b (1.1) corresponding to 100 Gy dose indicate that the peak follows first order kinetics The activation energy is consistent with the previous initial rise 3.3.3 Curve fitting technique The kinetic parameters of the main glow peak were further evaluated by curve fitting using the expression, ( )[ E T − TM 2kTM b I(T) = IM bb− exp + (b − 1) kT TM E ( ( ))]b−− b1 )( 2kT T E T − TM exp (2) +(b − 1) x − E kT TM TM2 Fig Results of curve fitting for the main peak in aquamarine irradiated to 100 Gy and read out at ◦ C/s the activation energy corresponding to 8, 40 and 100 Gy are (0.76 ± 0.01), (0.86 ± 0.01) and (0.89 ± 0.01) eV respectively where TM is the temperature corresponding to the maximum TL in­ tensity IM (Kitis et al., 1998) The goodness of fit was tested by the Figure of Merit (FOM) (Balian and Eddy, 1977) The values of FOM are considered acceptable if they are less than 3% Fig shows a fit of Eq (3) to the main peak in a measurement following beta irradiation to 100 Gy The frequency factor was 3.3.2 Whole glow peak method The whole glow peak method is based on use of the area under a glow peak Using this method, the order of kinetics, activation energy and effective frequency factor were evaluated According to the theory, the Fig The peak intensity of the main peak of aquamarine for 12 repeated identical measurements for different irradiation doses J Herrera et al calculated by using the following expression: ) ( βE E ( 2kTM )) exp s= ( kTM kTM + (b − 1) E Radiation Measurements 155 (2022) 106806 carried out at a heating rate of ◦ C/s The glow curve consists of the main peak at 75 ◦ C and three secondary peaks at 113, 188 and 306 ◦ C The position of the main peak is independent of dose between 0.1 and 100 Gy, a behavior suggestive of first order kinetics Kinetic analysis of the main peak was done using the initial rise, whole glow peak and curve fitting methods all of which also show that the peak follows first order kinetics Its activation energy is of the order of eV with a frequency factor of ~1012 s− The reproducibility of the peak is favorable (3) Using the curve fitting method on the main peak as described, the value of the activation energy is (0.96 ± 0.01) eV; the order of kinetics (b) is 1.27 ± 0.01 and frequency factor is 7.60 × 1012 s− The best fit was obtained with an FOM of 2.45% These values can be compared with ones from the other methods The activation energy, frequency factor and order of kinetics are comparable with those from other methods used earlier Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper 3.4 Reproducibility For reproducibility analysis, twelve identical measurements were carried out on a sample after irradiation to a given dose Fig shows the peak intensity against the number of measurements for the main peak for doses 1, 10, 20 and 40 Gy The intensity of the peak is consistent for the 12 cycles of measurements used For 1, 10, 20 and 40 Gy beta irradiation, the coefficient of variation (CV) in the results of 12 identical measurements in each found to be about 2, 0.8, 0.5 and 0.8% respec­ tively This shows that the material properly replicates its response under identical experimental conditions The decrease in CV with in­ crease in irradiation dose indicates that the reproducibility in general improves with dose References Balian, H., Eddy, N., 1977 Figure of Merit (FOM), an improved criterion over the normalized Chi-squared Test for assessing goodness of fit of Gamma Ray Nucl Instrum Methods B 145, 389–395 https://doi.org/10.1016/0029-554X(77)904372 Chithambo, M.L., Raymond, S.G., Calderon, T., Townsend, P.D., 1995 Low temperature luminescence of transition metal-doped beryls J Afr Earth Sci 20, 53–60 https:// doi.org/10.1016/0899-5362(95)00044-T Kati, M.I., Türemis, M., Keskin, I.C., Tastekin, B., Kibar, R., Çetin, A., Can, N., 2012 Luminescence behaviour of beryl (aquamarine variety) from Turkey J Lumin 2599–2602 https://doi.org/10.1016/j.jlumin.2012.03.058 Kittis, G., G´ omez-Ros, J.M., Tuyn, J., 1998 Thermoluminescence glow curve deconvolution functions for first, second and general order of kinetics J Phys D Appl Phys 31, 2636–2641 McKeever, S.W., Chen, R., 1997 Luminescence models Radiat Meas 27, 625–661 https://doi.org/10.1016/S1350-4487(97)00203-5 Pagonis, V., Kitis, G., Furetta, C., 2006 Numerrical and Practical Exercises in Thermoluminescence, first ed Springer, New York, NY https://doi.org/10.1007/0387-30090-2 Conclusions The TL of aquamarine, a pale blue hue variety of beryl (Be3Al2(­ SiO3)6) has been studied Samples were irradiated at room temperature using a90Sr/90Y β source at a rate of 0.10 Gys-1 Measurements were ... main peak recorded after irradiation at 8, 40 and 100 Gy The values of J Herrera et al Radiation Measurements 155 (2022) 106806 area n under a glow peak is related to the order of kinetics b as... The TL of aquamarine, a pale blue hue variety of beryl (Be3Al2(­ SiO3)6) has been studied Samples were irradiated at room temperature using a9 0Sr/90Y β source at a rate of 0.10 Gys-1 Measurements... Herrera et al Radiation Measurements 155 (2022) 106806 Fig Glow curve of aquamarine measured at ◦ C/s after irradiation at 8, 40 and 100 Gy of beta dose The inset shows the lower intensity peaks at