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Defect centre responsible for production of 110 ∘ C TL peak in quartz
Solid State Communications 149 (2009) 1173–1175
Contents lists available at ScienceDirect
Solid State Communications journal homepage: www.elsevier.com/locate/ssc
Defect centre responsible for production of 110 ◦ C TL peak in quartz T.M.B. Farias, S. Watanabe, T.K. Gundu Rao ∗ Institute of Physics, University of Sao Paulo, Sao Paulo, CEP: 05508-090, Brazil
article
info
Article history: Received 11 February 2009 Received in revised form 4 April 2009 Accepted 1 May 2009 by P. Chaddah Available online 7 May 2009 PACS: 70 Keywords: C. Defect centres C. Quartz D. Thermoluminescence
abstract 110 ◦ C thermoluminescence (TL) peak in quartz is well known due to its pre-dose effect, which is used in dating technique. The generally accepted mechanism for the production of this peak is based on Ge impurity contained in quartz. Its role is to substitute for Si in SiO4 tetrahedron and under irradiation gives rise to [GeO4 /e− ]− electron centre. Heating for TL read out liberates electron that recombines with hole in [AlO4 /h]◦ or [H3 O4 /h]◦ centres emitting photon. The investigation, carried out on blue quartz, green quartz, black quartz, pink quartz, red quartz, sulphurous quartz, milky quartz, alpha quartz and synthetic quartz, has shown that the 110 ◦ C TL peak in all these varieties of quartz has no correlation with the respective Ge content. Electron paramagnetic resonance (EPR) measurements on any of these varieties of quartz revealed a signal with g1 = 2.0004, g2 = 1.9986 and g3 = 1.974 and this signal does not appear to correspond to any known EPR signals in alpha quartz. Furthermore, isothermal decay measurements are carried out on the above mentioned EPR signal and 110 ◦ C TL peak in alpha, blue and green quartz. A close correlation has been observed in the decay behavior. A new mechanism is proposed based on an interstitial O− centre. © 2009 Elsevier Ltd. All rights reserved.
heat
1. Introduction
[GeO4 /e− ]− −−→ [GeO4 ]◦ + e−
110 ◦ C thermoluminescence (TL) peak in quartz is unstable at room temperature. However, it keeps memory of previous irradiation, which is known as pre-dose effect. This effect gives rise to a useful dating technique. For this reason it has received considerable attention from many researchers. The emitted TL light has two maxima, one around 380 nm and another less intense one around 470 nm [1]. McKeever et al. [2] has proposed that germanium substituting for Si in SiO4 tetrahedron is an electron trap associated with the 110 ◦ C TL peak. In fact [GeO4 ]◦ captures an electron during irradiation giving rise to the [GeO4 /e−]− centre. Irradiation also produces two other defect centres. One is the aluminum centre that is formed by removing alkali M+ -ion from the [AlO4 /M+ ]◦ namely: irrad
[AlO4 /M + ]o −−→ [AlO4 /h]◦ + M + .
(1)
The second one is [H4 O4 ]◦ that captures a hole and produces [H3 O4 /h]◦ centre. The heat during TL read out emits photons through the following reactions:
e + [AlO4 /h] + M −
◦
+
e + [H3 O4 /h] + H −
◦
+
(2)
→ [AlO4 /M ] + photon (470 nm)
(3)
→ [H4 O4 ] + photon (380 nm).
(4)
+ ◦
◦
The [H3 O4 /h] centre was first suggested by Yang and McKeever [3] to be associated with the 110 ◦ C TL peak. ◦
2. Materials and methods In the study, nine varieties of quartz have been investigated; they are blue quartz, green quartz, milky quartz, sulphurous quartz, black quartz, pink quartz, red quartz, alpha quartz and synthetic quartz. X-ray fluorescence analysis and ICP-MS analysis were used to determine the main impurity contents and X-ray diffraction technique was utilized for structure analysis. For irradiation with gamma rays from 60 Co source, care was exercised to carry out the irradiation at freezing temperature, which was maintained until the TL read out and EPR measurements. The TL glow curves have been obtained for samples irradiated to 1000 Gy and the EPR decay measurements were carried out at room temperature using 3000 Gy irradiated samples. 3. Results and discussion
∗ Corresponding address: T.K. Gundu Rao, c/o Prof. S. Watanabe, Instituto de Fisica-USP, Rua do Matão, travessa R, 187 – São Paulo/SP, CEP: 05508-090 – Brazil. E-mail address: [email protected] (T.K. Gundu Rao). 0038-1098/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2009.05.001
The results of X-ray diffraction measurements have shown that all nine varieties of quartz have diffraction patterns that match that of standard alpha quartz.
1174
T.M.B. Farias et al. / Solid State Communications 149 (2009) 1173–1175
Table 1 Concentration of Ge in wt% by ICP-MS. Alpha
Blue
Green
Black
Pink
Red
Sulphurous
Milky
Synthetic
0.0013
0.148
0.111
0.617
0.269
0.278
<0.001
1.904
0.101
Fig. 1. Tl glow curves of nine varieties of quartz.
X-ray fluorescence measurements indicated that the Ge concentrations in different quartz samples are less than the detectable limit. Ge concentrations were measured by ICP-MS and Table 1 gives the Ge concentration values in all nine varieties of quartz. Fig. 1 shows the glow curves of nine varieties of quartz. The accuracy of TL peak temperatures is ±5 ◦ C. The peak appears displaced to 85 ◦ C in pink and blue, to 90 ◦ C in green, milky and black and to 135 ◦ C in alpha quartz. Note that in the same scale 220 ◦ C and 325 ◦ C peaks appear very small compared to 110 ◦ C peak intensity. However, the striking fact is that the sulphurous quartz, which has a very low Ge concentration, presents a reasonably large 110 ◦ C peak. The 110 ◦ C TL peak in blue quartz with 0.148 wt% Ge is a bit larger than in alpha quartz which has 0.0013 wt% Ge and so on. There appears to be no correlation between Ge concentration and 110 ◦ C peak height. Fig. 2(a) shows an EPR signal (centre I) that is observed only for samples kept around freezing temperature during irradiation and also till the start of EPR measurements. The observed spectrum in Fig. 2(a) is a superposition of centre I EPR signal and also the Ge centre signal which is inidicated as centre II. Fig. 2(b) shows the Ge centre signal that remains after centre I has completely decayed at room temperature. Centre I is characterized by a rhombic gtensor with principal values g1 = 2.0004, g2 = 1.9986 and g3 = 1.974. Simultaneous decay measurements have been carried out on centre I EPR signal and 110 ◦ C TL peak. Fig. 3 shows respectively the decay curves of centre I EPR intensity and 110 ◦ C TL peak intensity; the decay curves are similar, indicating that centre I and the defect centre correlating with the 110 ◦ C peak TL are probably the same. At this point it may be concluded that centre I and not Ge centre (centre II) is the likely centre responsible for the 110 ◦ C TL peak. Now the question is: which defect centre is responsible for the 110 ◦ C TL emissions? A tentative answer is as follows. Bill [4] reported a possible existence of a O− centre in CaF2 substituting for F− ions. Its EPR signal has g-values given by gk = 1.995 and g⊥ = 2.105. Stapelbroek et al. [5] identified two distinct oxygenassociated trapped hole centres (OHC) in room temperature gamma-irradiated high-purity fused silica samples. One was called ‘‘wet’’ OHC, occurring in high-OH content silica and the other, the ‘‘dry’’ OHC in low-OH content sample. Their EPR spectra are
Fig. 2. EPR spectra of irradiated alpha quartz (dose: 3000 Gy). (a) Immediately after irradiation and (b) spectrum recorded after the decay of centre I.
(
)
Fig. 3. Decay curves of centre I (EPR) and 110 ◦ C TL peak.
characterized by g1 = 2.0010, g2 = 2.0095 and g3 = 2.078 in ‘‘wet’’ OHC and g1 = 2.0014, g2 = 2.0074 and g3 = 2.067 in ‘‘dry’’ OHC. These g-values indicate that neither ‘‘wet’’ nor ‘‘dry’’ OHC centres are the centre observed in the present work (centre I). It is known that any quartz, crystal or silica, has a large concentration of oxygen vacancies. Where do the the liberated oxygen ions move to? Some of them might migrate to the surface, but many of them will be trapped in the channel. Isoya et al. [6] have indicated two possible sites along c-axis in the channel for an interstitial atom or ion. It is quite possible that the oxygen ions evicted from their normal site will move to such a interstitial site after loosing two electrons, i.e., as neutral oxygen. In the next irradiation of the crystal, an electron is liberated by the radiation and is trapped by the neutral oxygen to form an O− ion, which attracts an M+ ion to compensate the charge. This complex is unstable at room temperature. If, however, the crystal is irradiated at freezing (lower) temperature, the radiation removes M+ ion in the complex O− M+ and the subsequent heating for TL read out liberates an electron to the conduction band and then recombines with the hole at the recombination centre and emits 110 ◦ C
T.M.B. Farias et al. / Solid State Communications 149 (2009) 1173–1175
TL photon. The electron in O− centre is likely to give rise to an EPR signal which is indicated as being to centre I in Fig. 1(a).
1175
Acknowledgment This work is supported by grants from FAPESP and CNPq.
4. Conclusions References 110 ◦ C TL peak intensity and Ge content measurements in eight varieties of natural quartz revealed that there is no correlation between them. Therefore, one may conclude that Ge cannot be a source of 110 ◦ C TL emission in quartz. O− centre resulting from an interstitial neutral oxygen inside the channel is proposed to be the likely source of electron that gives rise to the 110 ◦ C TL peak.
[1] [2] [3] [4] [5]
R.A. Akber, G.B. Robertson, J.R. Prescott, Nucl. Tracks Radiat. Meas. 14 (1988) 21. S.W.S. McKeever, C.Y. Chen, L.E. Halliburton, Nucl. Tracks 10 (1985) 489. X.H. Yang, S.W.S. McKeever, Nucl. Tracks Radiat. Meas. 14 (1988) 75. H. Bill, Solid State Commun. 9 (1971) 477. M. Stapelbroek, D.L. Griscom, E.J. Friebele, G.H. Sigel, J. Non-crystal. Solids 32 (1979) 313. [6] J. Isoya, W.C. Tennant, J.A. Weil, J. Magn. Reson. 79 (1988) 90.
Contents lists available at ScienceDirect
Solid State Communications journal homepage: www.elsevier.com/locate/ssc
Defect centre responsible for production of 110 ◦ C TL peak in quartz T.M.B. Farias, S. Watanabe, T.K. Gundu Rao ∗ Institute of Physics, University of Sao Paulo, Sao Paulo, CEP: 05508-090, Brazil
article
info
Article history: Received 11 February 2009 Received in revised form 4 April 2009 Accepted 1 May 2009 by P. Chaddah Available online 7 May 2009 PACS: 70 Keywords: C. Defect centres C. Quartz D. Thermoluminescence
abstract 110 ◦ C thermoluminescence (TL) peak in quartz is well known due to its pre-dose effect, which is used in dating technique. The generally accepted mechanism for the production of this peak is based on Ge impurity contained in quartz. Its role is to substitute for Si in SiO4 tetrahedron and under irradiation gives rise to [GeO4 /e− ]− electron centre. Heating for TL read out liberates electron that recombines with hole in [AlO4 /h]◦ or [H3 O4 /h]◦ centres emitting photon. The investigation, carried out on blue quartz, green quartz, black quartz, pink quartz, red quartz, sulphurous quartz, milky quartz, alpha quartz and synthetic quartz, has shown that the 110 ◦ C TL peak in all these varieties of quartz has no correlation with the respective Ge content. Electron paramagnetic resonance (EPR) measurements on any of these varieties of quartz revealed a signal with g1 = 2.0004, g2 = 1.9986 and g3 = 1.974 and this signal does not appear to correspond to any known EPR signals in alpha quartz. Furthermore, isothermal decay measurements are carried out on the above mentioned EPR signal and 110 ◦ C TL peak in alpha, blue and green quartz. A close correlation has been observed in the decay behavior. A new mechanism is proposed based on an interstitial O− centre. © 2009 Elsevier Ltd. All rights reserved.
heat
1. Introduction
[GeO4 /e− ]− −−→ [GeO4 ]◦ + e−
110 ◦ C thermoluminescence (TL) peak in quartz is unstable at room temperature. However, it keeps memory of previous irradiation, which is known as pre-dose effect. This effect gives rise to a useful dating technique. For this reason it has received considerable attention from many researchers. The emitted TL light has two maxima, one around 380 nm and another less intense one around 470 nm [1]. McKeever et al. [2] has proposed that germanium substituting for Si in SiO4 tetrahedron is an electron trap associated with the 110 ◦ C TL peak. In fact [GeO4 ]◦ captures an electron during irradiation giving rise to the [GeO4 /e−]− centre. Irradiation also produces two other defect centres. One is the aluminum centre that is formed by removing alkali M+ -ion from the [AlO4 /M+ ]◦ namely: irrad
[AlO4 /M + ]o −−→ [AlO4 /h]◦ + M + .
(1)
The second one is [H4 O4 ]◦ that captures a hole and produces [H3 O4 /h]◦ centre. The heat during TL read out emits photons through the following reactions:
e + [AlO4 /h] + M −
◦
+
e + [H3 O4 /h] + H −
◦
+
(2)
→ [AlO4 /M ] + photon (470 nm)
(3)
→ [H4 O4 ] + photon (380 nm).
(4)
+ ◦
◦
The [H3 O4 /h] centre was first suggested by Yang and McKeever [3] to be associated with the 110 ◦ C TL peak. ◦
2. Materials and methods In the study, nine varieties of quartz have been investigated; they are blue quartz, green quartz, milky quartz, sulphurous quartz, black quartz, pink quartz, red quartz, alpha quartz and synthetic quartz. X-ray fluorescence analysis and ICP-MS analysis were used to determine the main impurity contents and X-ray diffraction technique was utilized for structure analysis. For irradiation with gamma rays from 60 Co source, care was exercised to carry out the irradiation at freezing temperature, which was maintained until the TL read out and EPR measurements. The TL glow curves have been obtained for samples irradiated to 1000 Gy and the EPR decay measurements were carried out at room temperature using 3000 Gy irradiated samples. 3. Results and discussion
∗ Corresponding address: T.K. Gundu Rao, c/o Prof. S. Watanabe, Instituto de Fisica-USP, Rua do Matão, travessa R, 187 – São Paulo/SP, CEP: 05508-090 – Brazil. E-mail address: [email protected] (T.K. Gundu Rao). 0038-1098/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2009.05.001
The results of X-ray diffraction measurements have shown that all nine varieties of quartz have diffraction patterns that match that of standard alpha quartz.
1174
T.M.B. Farias et al. / Solid State Communications 149 (2009) 1173–1175
Table 1 Concentration of Ge in wt% by ICP-MS. Alpha
Blue
Green
Black
Pink
Red
Sulphurous
Milky
Synthetic
0.0013
0.148
0.111
0.617
0.269
0.278
<0.001
1.904
0.101
Fig. 1. Tl glow curves of nine varieties of quartz.
X-ray fluorescence measurements indicated that the Ge concentrations in different quartz samples are less than the detectable limit. Ge concentrations were measured by ICP-MS and Table 1 gives the Ge concentration values in all nine varieties of quartz. Fig. 1 shows the glow curves of nine varieties of quartz. The accuracy of TL peak temperatures is ±5 ◦ C. The peak appears displaced to 85 ◦ C in pink and blue, to 90 ◦ C in green, milky and black and to 135 ◦ C in alpha quartz. Note that in the same scale 220 ◦ C and 325 ◦ C peaks appear very small compared to 110 ◦ C peak intensity. However, the striking fact is that the sulphurous quartz, which has a very low Ge concentration, presents a reasonably large 110 ◦ C peak. The 110 ◦ C TL peak in blue quartz with 0.148 wt% Ge is a bit larger than in alpha quartz which has 0.0013 wt% Ge and so on. There appears to be no correlation between Ge concentration and 110 ◦ C peak height. Fig. 2(a) shows an EPR signal (centre I) that is observed only for samples kept around freezing temperature during irradiation and also till the start of EPR measurements. The observed spectrum in Fig. 2(a) is a superposition of centre I EPR signal and also the Ge centre signal which is inidicated as centre II. Fig. 2(b) shows the Ge centre signal that remains after centre I has completely decayed at room temperature. Centre I is characterized by a rhombic gtensor with principal values g1 = 2.0004, g2 = 1.9986 and g3 = 1.974. Simultaneous decay measurements have been carried out on centre I EPR signal and 110 ◦ C TL peak. Fig. 3 shows respectively the decay curves of centre I EPR intensity and 110 ◦ C TL peak intensity; the decay curves are similar, indicating that centre I and the defect centre correlating with the 110 ◦ C peak TL are probably the same. At this point it may be concluded that centre I and not Ge centre (centre II) is the likely centre responsible for the 110 ◦ C TL peak. Now the question is: which defect centre is responsible for the 110 ◦ C TL emissions? A tentative answer is as follows. Bill [4] reported a possible existence of a O− centre in CaF2 substituting for F− ions. Its EPR signal has g-values given by gk = 1.995 and g⊥ = 2.105. Stapelbroek et al. [5] identified two distinct oxygenassociated trapped hole centres (OHC) in room temperature gamma-irradiated high-purity fused silica samples. One was called ‘‘wet’’ OHC, occurring in high-OH content silica and the other, the ‘‘dry’’ OHC in low-OH content sample. Their EPR spectra are
Fig. 2. EPR spectra of irradiated alpha quartz (dose: 3000 Gy). (a) Immediately after irradiation and (b) spectrum recorded after the decay of centre I.
(
)
Fig. 3. Decay curves of centre I (EPR) and 110 ◦ C TL peak.
characterized by g1 = 2.0010, g2 = 2.0095 and g3 = 2.078 in ‘‘wet’’ OHC and g1 = 2.0014, g2 = 2.0074 and g3 = 2.067 in ‘‘dry’’ OHC. These g-values indicate that neither ‘‘wet’’ nor ‘‘dry’’ OHC centres are the centre observed in the present work (centre I). It is known that any quartz, crystal or silica, has a large concentration of oxygen vacancies. Where do the the liberated oxygen ions move to? Some of them might migrate to the surface, but many of them will be trapped in the channel. Isoya et al. [6] have indicated two possible sites along c-axis in the channel for an interstitial atom or ion. It is quite possible that the oxygen ions evicted from their normal site will move to such a interstitial site after loosing two electrons, i.e., as neutral oxygen. In the next irradiation of the crystal, an electron is liberated by the radiation and is trapped by the neutral oxygen to form an O− ion, which attracts an M+ ion to compensate the charge. This complex is unstable at room temperature. If, however, the crystal is irradiated at freezing (lower) temperature, the radiation removes M+ ion in the complex O− M+ and the subsequent heating for TL read out liberates an electron to the conduction band and then recombines with the hole at the recombination centre and emits 110 ◦ C
T.M.B. Farias et al. / Solid State Communications 149 (2009) 1173–1175
TL photon. The electron in O− centre is likely to give rise to an EPR signal which is indicated as being to centre I in Fig. 1(a).
1175
Acknowledgment This work is supported by grants from FAPESP and CNPq.
4. Conclusions References 110 ◦ C TL peak intensity and Ge content measurements in eight varieties of natural quartz revealed that there is no correlation between them. Therefore, one may conclude that Ge cannot be a source of 110 ◦ C TL emission in quartz. O− centre resulting from an interstitial neutral oxygen inside the channel is proposed to be the likely source of electron that gives rise to the 110 ◦ C TL peak.
[1] [2] [3] [4] [5]
R.A. Akber, G.B. Robertson, J.R. Prescott, Nucl. Tracks Radiat. Meas. 14 (1988) 21. S.W.S. McKeever, C.Y. Chen, L.E. Halliburton, Nucl. Tracks 10 (1985) 489. X.H. Yang, S.W.S. McKeever, Nucl. Tracks Radiat. Meas. 14 (1988) 75. H. Bill, Solid State Commun. 9 (1971) 477. M. Stapelbroek, D.L. Griscom, E.J. Friebele, G.H. Sigel, J. Non-crystal. Solids 32 (1979) 313. [6] J. Isoya, W.C. Tennant, J.A. Weil, J. Magn. Reson. 79 (1988) 90.