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Radiation damage of silicate glasses doped with Tb3+ and Eu3+
Journal of Non-Crystalline Solids 315 (2003) 271–275 www.elsevier.com/locate/jnoncrysol
Radiation damage of silicate glasses doped with Tb3þ and Eu3þ S. Baccaro
a,*
, A. Cecilia a, M. Montecchi a, M. Nikl b, P. Polato c, G. Zanella d, R. Zannoni d
a
ENEA-FIS/ION, Via Anguillarese 301, 00060 S. Maria di Galeria, Rome, Italy Institute of Physics AS CR, Cukrovarnicka 10, 162 53 Prague, Czech Republic c Stazione Sperimentale del Vetro, Via Briati 10, 30121 Murano-Venezia, Italy Department of Physics, INFN, University of Padova, Via Marzolo 8, 35131 Padova, Italy b
d
Received 28 November 2001; received in revised form 31 May 2002
Abstract In this work, we studied a set of Tb3þ (or Eu3þ ) doped silicate glasses in which some amounts of BaO were added to increase glass density. The irradiation-induced damage was investigated by absorbance measurements performed before and after each irradiation with doses ranging from 3 to 237 Gy. Analysed glasses underwent also light yield measurements investigated in terms of light production. The results showed that radiation damage and light yield depend on glass composition and are very low for the Eu3þ containing glass and for the Tb3þ activated glass which contains also lead. A possible explanation could be that lead and europium favour in the glass matrix the formation of a higher concentration of defects with respect to Tb3þ doping ions. Ó 2003 Elsevier Science B.V. All rights reserved.
1. Introduction Glass scintillators offer some advantages with respect to scintillating crystals: glasses are much cheaper than crystals, and can be more easily shaped. Moreover, scintillating glasses can be used in bulk or fibre form for the detection of X-ray [1]. For a long time scintillating glasses have been investigated very little in comparison with single crystals, because they generally suffer from low transfer efficiency due to the presence of traps that
*
Corresponding author. Tel.: +39-6 3048 4873; fax: +39-6 3048 4875. E-mail address: [email protected] (S. Baccaro).
are possible centres of non radiative recombination [2]. Recently, we have shown the possibility to enhance the glass energy transfer efficiency by introducing in the glass matrix Gd3þ ions that favour the energy transfer to emission centres [2–5]. Among the ions used to optically activate glass matrices, Tb3þ and Eu3þ are frequently used. They are characterised by different emission spectra [6]. The emission spectrum of Tb3þ is composed of four leading lines at 482, 542.5, 585 and 621 nm belonging to the electronic transitions 5 D4 ! 7 FX (X ¼ 6, 5, 4, 3 respectively) of Tb3þ . The greatest part of energy is emitted at 542.5 nm. Concerning the decay kinetics, its scintillation is slow with a decay time of 3.0 ms in silicate glasses. The Eu3þ luminescence spectrum is composed of two bands
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centred around 591 and 613 nm with a decay time of 2 ms about. The first peak is due to the 5 D0 ! 7 F1 transition; the second (the dominating one) is due to the 5 D0 ! 7 F2 transition [6]. The radiation hardness is a fundamental parameter for the characterisation of scintillating materials. Ionising radiation could induce the formation of colour centres, which might reabsorb the scintillating light, causing the degradation of both sensitivity and energy resolution of scintillator. In order to study the radiation hardness dependence on glass composition and on the kind of activator (Tb3þ or Eu3þ ) we have analysed four silicate glasses having compositions reported in Table 1. Ba2þ ions were added in all compositions in order to increase density; moreover, to further an increased density, part of Ba2þ content was substituted with Pb2þ (glass #3). All samples were irradiated at the 60 Co radioisotope source ÔCalliopeÕ (ENEA-Casaccia, Rome) with a dose rate of 3.1 Gy/h. The imparted doses ranged between 3 and 237 Gy in air. Before and after each irradiation, samples underwent absorbance measurements. From these data, the radiation induced absorption coefficient (l) was calculated according to the formula l¼
2:3 lnðA A0 Þ; L
where L, A0 and A stand for sample length (m) and absorbance before and after irradiation, respectively. Before each irradiation, glasses were thermally bleached (4 h at 650 °C) in order to restore the initial conditions. To study the dependence of the light production on the glass composition, the samples were also
Table 1 Composition of analysed glasses Sample #1 #2 #3 #4
Composition (wt%) Tb2 O3
Eu2 O3
Gd2 O3
BaO
PbO
Length (mm)
10 10 10 –
– – – 10
3 3 3 3
36 25 15 36
– – 20 –
20 20 20 20
submitted to light yield measurements. The apparatus mainly consists of a X-ray tube, having a molybdenum anode, and a photographic emulsion, with constant sensitivity in the range 400–600 nm. Single X-ray pulses were obtained by applying 25 kV for 125 ms. The samples were put in contact with the photographic emulsion. The light yield value is proportional to the opacity of the negative image impressed on the plate. For each glass, a tablet having a diameter of 15 mm, a thickness of 2 mm and with both faces polished was prepared. In order to make easier the comparison, all the samples were irradiated at the same time with a uniform X-ray beam. Together with them, a 2 mm thick tablet of a known Ce3þ doped scintillating glass (GS1, produced by Levy Hill Laboratories 1) was also irradiated. The GS1 sample has previously been submitted to absolute light yield measurements and was here considered as reference sample. Almost the totality of the ionising radiation travelling across GS1 is absorbed giving an absolute light yield of about 10 ph/keV (at its maximum emission of 400 nm) considering the fast decay component plus the slow decay component [7–10].
2. Experimental results By comparing the initial absorbance spectra of the as grown glasses (Fig. 1) one can see that glasses #1 and #2 show Tb3þ typical absorption bands around 3.3 and 2.6 eV. In the Tb3þ activated glass containing lead (#3), these bands are strongly reduced and the absorbance between 3.2 and 4.1 eV is lower respect to those of glasses #1 and #2. The absorbance of sample #4 is higher respect to the other samples and shows the typical Eu3þ absorption bands located around 3.3, 3.2, 2.7 and 2.3 eV (transition 7 Fx ! 5 Dx ) [6]. As far as the effect of ionising irradiation is concerned, it induces an increase in absorbance higher as the dose increases, as it is shown in Fig. 2 for glass #2.
1 5 Sheffield House, Fieldings Rd, Cheshunt Herts., EN8 9TJ, UK.
S. Baccaro et al. / Journal of Non-Crystalline Solids 315 (2003) 271–275
273
Fig. 1. Absorbance curves of the as grown glasses.
Fig. 3. Radiation-induced absorption coefficient of glasses at the highest irradiation dose.
Fig. 2. Absorbance curves of glass #2 at the different irradiation doses.
Fig. 4. Radiation-induced absorption coefficient of glasses at the activator proper emission wavelengths (k ¼ 542:5 nm for glasses #1, #2 and #3; k ¼ 613 nm for glass #4).
Fig. 3 shows the radiation-induced absorption coefficient calculated for each sample at all imparted doses. For what concerns the c radiation induced absorption bands, they depend on the kind of activator. In the Eu3þ doped glass (#4) radiation induces the formation of an absorption band extending from 4.1 to 1.6 eV. In the Tb3þ doped glasses, a broad absorption band is induced by ionising radiation extending from the band-edge up to 2.5 eV; glass #3 has an exceptional behaviour, respect to the other terbium containing glasses, because it shows a further absorption band around 1.7 eV.
For the practical application, the wavelength of interest for the study of radiation hardness is the characteristic one at which activator ions emit, that are 2.28 eV (542.5 nm) and 2.02 eV (613 nm) respectively for terbium and europium. Fig. 4 reports the plot of the l calculated at the proper emission wavelengths in function of the imparted doses for all samples.
3. Discussion About the radiation effect, when as grown glass matrices are submitted to ionising irradiation,
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S. Baccaro et al. / Journal of Non-Crystalline Solids 315 (2003) 271–275
intrinsic defects pairs composed of hole centres (HC) and corresponding electron centres (EC) are formed due to the release and capture of electrons by precursors in the glass matrix [11]. If the irradiated matrices contain doping ions, such as Tb3þ or Eu3þ , the irradiation can affect the valence state of dopants that can consequently serve as HC or EC. In the case of Tb3þ and Eu3þ doped glasses, ionising irradiation can prime the following redoxreactions: þ
Tb3þ þ c ) ðTb3þ Þ þ EC
Eu3þ þ c ) ðEu3þ Þ þ HC which oxidise Tb3þ to ðTb3þ Þþ and reduce Eu3þ to ðEu3þ Þ [11,12]. þ The radiation induced ðTb3þ Þ and ðEu3þ Þ ions are characterized by typical UV–VIS absorption transitions that in the first case are related to charge transfer transition (CT) from the ligands þ to the rare earth ðTb3þ Þ ion and in the second 3þ case are due to ðEu Þ 4f ) 5d absorption transition. ðTb3þ Þþ ion is characterised by a CT absorption band centred around 3.3 eV and extending up to 2.2 eV; ðEu3þ Þ gives rise to absorption transitions between 4.1 and 3.3 eV [11,12]. Starting from these considerations, we may hypothesise that the broad band observed in Tb3þ doped glasses after irradiation is probably related to radiation induced ðTb3þ Þþ HC [13]. The radiation-induced absorption observed on Eu3þ doped glass seems to be the superposition of two bands, one centred around 3.9 eV and the other around 2.7 eV. The first band is probably related to radiation induced ðEu3þ Þ ions while the second one should be further investigated to understand its origin. A point to be stressed is that the radiation damage at the proper ions emission wavelength (Fig. 4) is almost the same for the Tb3þ doped glasses #1 and #2 while for the glass #3, doped with Tb3þ and containing also lead, the damage is much higher. This effect is probably due to the presence of lead ions well known for easily variable charge states, which may induce additional traps in the glass matrix where charge carriers can be entrapped after being moved by
irradiation. The radiation hardness of Eu3þ doped glass is very similar to that of glass containing lead and is quite higher when compared to the other samples, indicating that from the radiation hardness point of view Tb3þ ions are much more suitable than Eu3þ to optically activate scintillating glasses. As far as the light yield measurements are concerned, we observed that the light production of glass #1 is around 20 ph/keV and the one related to sample #2 is 12 ph/keV. This difference is probably due to the lower transmission of the glass #2 respect to the other, which implies a less collection of light on the photomultiplier. Samples #3 and #4 show drastic loss of light yield (about one order of magnitude) with values of 1 and 2 ph/keV respectively, at the maximum of emission. A possible explanation of this effect could be that Eu3þ and lead induce in the glass matrix the formation of traps that reabsorb scintillating light.
4. Conclusions From all the obtained results, a clear correlation among radiation damage, light yield and glass composition is evident. The radiation damage and light yield are the lowest for the europium containing glass and for the terbium doped glass containing also lead. These results indicate that Tb3þ is much more suitable than Eu3þ to optically activate glass matrices; it is also evident that it is not possible to add lead to increase density, because such ions negatively influence the scintillator performances. A possible explanation could be that lead and europium introduce traps in the matrix where charge carriers can be entrapped after being moved by irradiation. These defects reabsorb a fraction of the scintillating light with a consequent decrease of light yield.
Acknowledgement The authors are grateful for the financial support to the NEWLUMEN experiment supported by Gruppo V, INFN (Italy).
S. Baccaro et al. / Journal of Non-Crystalline Solids 315 (2003) 271–275
References [1] G. Zanella, R. Zannoni, NIMA 287 (1990) 619. [2] S. Baccaro, R. DallÕIgna, P. Fabeni, M. Martini, J.A. Mares, F. Meinardi, E. Mihokova, M. Nikl, K. Nitsch, G.P. Pazzi, P. Polato, A. Vedda, G. Zanella, R. Zannoni, in: V.V. Mikhailin (Ed.), Proceedings of 5th International Conference on Inorganic Scintillators and their Applications, SCINT99, Moscow, 16–20 August 1999, p. 106. [3] M. Nikl, K. Nitsch, E. Mihokova, N. Solovieva, J.A. Mares, P. Fabeni, G.P. Pazzi, M. Martini, A. Vedda, S. Baccaro, Appl. Phys. Lett. 77 (2000) 2159. [4] S. Baccaro, R. DallÕIgna, P. Fabeni, M. Martini, J.A. Mares, M. Martini, M. Nikl, G.P. Pazzi, P. Polato, A. Vedda, G. Zanella, R. Zannoni, in: Glass Science and Technology for the 21th century––5th ESG Conference, Prague, June 1999, p. C1-23. [5] S. Baccaro, R. DallÕIgna, P. Fabeni, M. Martini, J.A. Mares, F. Meinardi, M. Nikl, K. Nitsch, G.P. Pazzi, P.
[6] [7] [8] [9] [10] [11] [12]
[13]
275
Polato, C. Susini, A. Vedda, G. Zanella, R. Zannoni, J. Lumin. 87&89 (2000) 673. M. Bettinelli, G. Ingletto, P. Polato, G. Pozza, G. Zanella, R. Zannoni, Phys. Chem. Glasses 37 (1) (1996) 4. S. Brollo, G. Zanella, R. Zannoni, NIMA 293 (1990) 601. G. Zanella, R. Zannoni, R. DallÕIgna, B. Locardi, P. Polato, M. Bettinelli, A. Marigo, NIMA 345 (1994) 198. G. Zanella, R. Zannoni, NIMA 302 (1991) 352. C. Angelini, G. Zanella, R. Zannoni, NIMA 281 (1989) 50. H. Ebendorff Heidepriem, D. Ehrt, Opt. Mater. 15 (2000) 7. H. Ebendorff Heidepriem, D. Ehrt, in: Glass Science and Technology for the 21th century––5th ESG Conference, Prague, June 1999, p. C1-62. M. Nikl, S. Baccaro, A. Cecilia, P. Fabeni, M. Martini, E. Mihokova, K. Nitsch, G.P. Pazzi, N. Solovieva, A. Vedda, in: 7th International Conference on Advanced Technology and Particle Physics, Villa Olmo, Como, Italy, 15–19 October 2001.
Radiation damage of silicate glasses doped with Tb3þ and Eu3þ S. Baccaro
a,*
, A. Cecilia a, M. Montecchi a, M. Nikl b, P. Polato c, G. Zanella d, R. Zannoni d
a
ENEA-FIS/ION, Via Anguillarese 301, 00060 S. Maria di Galeria, Rome, Italy Institute of Physics AS CR, Cukrovarnicka 10, 162 53 Prague, Czech Republic c Stazione Sperimentale del Vetro, Via Briati 10, 30121 Murano-Venezia, Italy Department of Physics, INFN, University of Padova, Via Marzolo 8, 35131 Padova, Italy b
d
Received 28 November 2001; received in revised form 31 May 2002
Abstract In this work, we studied a set of Tb3þ (or Eu3þ ) doped silicate glasses in which some amounts of BaO were added to increase glass density. The irradiation-induced damage was investigated by absorbance measurements performed before and after each irradiation with doses ranging from 3 to 237 Gy. Analysed glasses underwent also light yield measurements investigated in terms of light production. The results showed that radiation damage and light yield depend on glass composition and are very low for the Eu3þ containing glass and for the Tb3þ activated glass which contains also lead. A possible explanation could be that lead and europium favour in the glass matrix the formation of a higher concentration of defects with respect to Tb3þ doping ions. Ó 2003 Elsevier Science B.V. All rights reserved.
1. Introduction Glass scintillators offer some advantages with respect to scintillating crystals: glasses are much cheaper than crystals, and can be more easily shaped. Moreover, scintillating glasses can be used in bulk or fibre form for the detection of X-ray [1]. For a long time scintillating glasses have been investigated very little in comparison with single crystals, because they generally suffer from low transfer efficiency due to the presence of traps that
*
Corresponding author. Tel.: +39-6 3048 4873; fax: +39-6 3048 4875. E-mail address: [email protected] (S. Baccaro).
are possible centres of non radiative recombination [2]. Recently, we have shown the possibility to enhance the glass energy transfer efficiency by introducing in the glass matrix Gd3þ ions that favour the energy transfer to emission centres [2–5]. Among the ions used to optically activate glass matrices, Tb3þ and Eu3þ are frequently used. They are characterised by different emission spectra [6]. The emission spectrum of Tb3þ is composed of four leading lines at 482, 542.5, 585 and 621 nm belonging to the electronic transitions 5 D4 ! 7 FX (X ¼ 6, 5, 4, 3 respectively) of Tb3þ . The greatest part of energy is emitted at 542.5 nm. Concerning the decay kinetics, its scintillation is slow with a decay time of 3.0 ms in silicate glasses. The Eu3þ luminescence spectrum is composed of two bands
0022-3093/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 0 2 ) 0 1 6 0 1 - 0
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S. Baccaro et al. / Journal of Non-Crystalline Solids 315 (2003) 271–275
centred around 591 and 613 nm with a decay time of 2 ms about. The first peak is due to the 5 D0 ! 7 F1 transition; the second (the dominating one) is due to the 5 D0 ! 7 F2 transition [6]. The radiation hardness is a fundamental parameter for the characterisation of scintillating materials. Ionising radiation could induce the formation of colour centres, which might reabsorb the scintillating light, causing the degradation of both sensitivity and energy resolution of scintillator. In order to study the radiation hardness dependence on glass composition and on the kind of activator (Tb3þ or Eu3þ ) we have analysed four silicate glasses having compositions reported in Table 1. Ba2þ ions were added in all compositions in order to increase density; moreover, to further an increased density, part of Ba2þ content was substituted with Pb2þ (glass #3). All samples were irradiated at the 60 Co radioisotope source ÔCalliopeÕ (ENEA-Casaccia, Rome) with a dose rate of 3.1 Gy/h. The imparted doses ranged between 3 and 237 Gy in air. Before and after each irradiation, samples underwent absorbance measurements. From these data, the radiation induced absorption coefficient (l) was calculated according to the formula l¼
2:3 lnðA A0 Þ; L
where L, A0 and A stand for sample length (m) and absorbance before and after irradiation, respectively. Before each irradiation, glasses were thermally bleached (4 h at 650 °C) in order to restore the initial conditions. To study the dependence of the light production on the glass composition, the samples were also
Table 1 Composition of analysed glasses Sample #1 #2 #3 #4
Composition (wt%) Tb2 O3
Eu2 O3
Gd2 O3
BaO
PbO
Length (mm)
10 10 10 –
– – – 10
3 3 3 3
36 25 15 36
– – 20 –
20 20 20 20
submitted to light yield measurements. The apparatus mainly consists of a X-ray tube, having a molybdenum anode, and a photographic emulsion, with constant sensitivity in the range 400–600 nm. Single X-ray pulses were obtained by applying 25 kV for 125 ms. The samples were put in contact with the photographic emulsion. The light yield value is proportional to the opacity of the negative image impressed on the plate. For each glass, a tablet having a diameter of 15 mm, a thickness of 2 mm and with both faces polished was prepared. In order to make easier the comparison, all the samples were irradiated at the same time with a uniform X-ray beam. Together with them, a 2 mm thick tablet of a known Ce3þ doped scintillating glass (GS1, produced by Levy Hill Laboratories 1) was also irradiated. The GS1 sample has previously been submitted to absolute light yield measurements and was here considered as reference sample. Almost the totality of the ionising radiation travelling across GS1 is absorbed giving an absolute light yield of about 10 ph/keV (at its maximum emission of 400 nm) considering the fast decay component plus the slow decay component [7–10].
2. Experimental results By comparing the initial absorbance spectra of the as grown glasses (Fig. 1) one can see that glasses #1 and #2 show Tb3þ typical absorption bands around 3.3 and 2.6 eV. In the Tb3þ activated glass containing lead (#3), these bands are strongly reduced and the absorbance between 3.2 and 4.1 eV is lower respect to those of glasses #1 and #2. The absorbance of sample #4 is higher respect to the other samples and shows the typical Eu3þ absorption bands located around 3.3, 3.2, 2.7 and 2.3 eV (transition 7 Fx ! 5 Dx ) [6]. As far as the effect of ionising irradiation is concerned, it induces an increase in absorbance higher as the dose increases, as it is shown in Fig. 2 for glass #2.
1 5 Sheffield House, Fieldings Rd, Cheshunt Herts., EN8 9TJ, UK.
S. Baccaro et al. / Journal of Non-Crystalline Solids 315 (2003) 271–275
273
Fig. 1. Absorbance curves of the as grown glasses.
Fig. 3. Radiation-induced absorption coefficient of glasses at the highest irradiation dose.
Fig. 2. Absorbance curves of glass #2 at the different irradiation doses.
Fig. 4. Radiation-induced absorption coefficient of glasses at the activator proper emission wavelengths (k ¼ 542:5 nm for glasses #1, #2 and #3; k ¼ 613 nm for glass #4).
Fig. 3 shows the radiation-induced absorption coefficient calculated for each sample at all imparted doses. For what concerns the c radiation induced absorption bands, they depend on the kind of activator. In the Eu3þ doped glass (#4) radiation induces the formation of an absorption band extending from 4.1 to 1.6 eV. In the Tb3þ doped glasses, a broad absorption band is induced by ionising radiation extending from the band-edge up to 2.5 eV; glass #3 has an exceptional behaviour, respect to the other terbium containing glasses, because it shows a further absorption band around 1.7 eV.
For the practical application, the wavelength of interest for the study of radiation hardness is the characteristic one at which activator ions emit, that are 2.28 eV (542.5 nm) and 2.02 eV (613 nm) respectively for terbium and europium. Fig. 4 reports the plot of the l calculated at the proper emission wavelengths in function of the imparted doses for all samples.
3. Discussion About the radiation effect, when as grown glass matrices are submitted to ionising irradiation,
274
S. Baccaro et al. / Journal of Non-Crystalline Solids 315 (2003) 271–275
intrinsic defects pairs composed of hole centres (HC) and corresponding electron centres (EC) are formed due to the release and capture of electrons by precursors in the glass matrix [11]. If the irradiated matrices contain doping ions, such as Tb3þ or Eu3þ , the irradiation can affect the valence state of dopants that can consequently serve as HC or EC. In the case of Tb3þ and Eu3þ doped glasses, ionising irradiation can prime the following redoxreactions: þ
Tb3þ þ c ) ðTb3þ Þ þ EC
Eu3þ þ c ) ðEu3þ Þ þ HC which oxidise Tb3þ to ðTb3þ Þþ and reduce Eu3þ to ðEu3þ Þ [11,12]. þ The radiation induced ðTb3þ Þ and ðEu3þ Þ ions are characterized by typical UV–VIS absorption transitions that in the first case are related to charge transfer transition (CT) from the ligands þ to the rare earth ðTb3þ Þ ion and in the second 3þ case are due to ðEu Þ 4f ) 5d absorption transition. ðTb3þ Þþ ion is characterised by a CT absorption band centred around 3.3 eV and extending up to 2.2 eV; ðEu3þ Þ gives rise to absorption transitions between 4.1 and 3.3 eV [11,12]. Starting from these considerations, we may hypothesise that the broad band observed in Tb3þ doped glasses after irradiation is probably related to radiation induced ðTb3þ Þþ HC [13]. The radiation-induced absorption observed on Eu3þ doped glass seems to be the superposition of two bands, one centred around 3.9 eV and the other around 2.7 eV. The first band is probably related to radiation induced ðEu3þ Þ ions while the second one should be further investigated to understand its origin. A point to be stressed is that the radiation damage at the proper ions emission wavelength (Fig. 4) is almost the same for the Tb3þ doped glasses #1 and #2 while for the glass #3, doped with Tb3þ and containing also lead, the damage is much higher. This effect is probably due to the presence of lead ions well known for easily variable charge states, which may induce additional traps in the glass matrix where charge carriers can be entrapped after being moved by
irradiation. The radiation hardness of Eu3þ doped glass is very similar to that of glass containing lead and is quite higher when compared to the other samples, indicating that from the radiation hardness point of view Tb3þ ions are much more suitable than Eu3þ to optically activate scintillating glasses. As far as the light yield measurements are concerned, we observed that the light production of glass #1 is around 20 ph/keV and the one related to sample #2 is 12 ph/keV. This difference is probably due to the lower transmission of the glass #2 respect to the other, which implies a less collection of light on the photomultiplier. Samples #3 and #4 show drastic loss of light yield (about one order of magnitude) with values of 1 and 2 ph/keV respectively, at the maximum of emission. A possible explanation of this effect could be that Eu3þ and lead induce in the glass matrix the formation of traps that reabsorb scintillating light.
4. Conclusions From all the obtained results, a clear correlation among radiation damage, light yield and glass composition is evident. The radiation damage and light yield are the lowest for the europium containing glass and for the terbium doped glass containing also lead. These results indicate that Tb3þ is much more suitable than Eu3þ to optically activate glass matrices; it is also evident that it is not possible to add lead to increase density, because such ions negatively influence the scintillator performances. A possible explanation could be that lead and europium introduce traps in the matrix where charge carriers can be entrapped after being moved by irradiation. These defects reabsorb a fraction of the scintillating light with a consequent decrease of light yield.
Acknowledgement The authors are grateful for the financial support to the NEWLUMEN experiment supported by Gruppo V, INFN (Italy).
S. Baccaro et al. / Journal of Non-Crystalline Solids 315 (2003) 271–275
References [1] G. Zanella, R. Zannoni, NIMA 287 (1990) 619. [2] S. Baccaro, R. DallÕIgna, P. Fabeni, M. Martini, J.A. Mares, F. Meinardi, E. Mihokova, M. Nikl, K. Nitsch, G.P. Pazzi, P. Polato, A. Vedda, G. Zanella, R. Zannoni, in: V.V. Mikhailin (Ed.), Proceedings of 5th International Conference on Inorganic Scintillators and their Applications, SCINT99, Moscow, 16–20 August 1999, p. 106. [3] M. Nikl, K. Nitsch, E. Mihokova, N. Solovieva, J.A. Mares, P. Fabeni, G.P. Pazzi, M. Martini, A. Vedda, S. Baccaro, Appl. Phys. Lett. 77 (2000) 2159. [4] S. Baccaro, R. DallÕIgna, P. Fabeni, M. Martini, J.A. Mares, M. Martini, M. Nikl, G.P. Pazzi, P. Polato, A. Vedda, G. Zanella, R. Zannoni, in: Glass Science and Technology for the 21th century––5th ESG Conference, Prague, June 1999, p. C1-23. [5] S. Baccaro, R. DallÕIgna, P. Fabeni, M. Martini, J.A. Mares, F. Meinardi, M. Nikl, K. Nitsch, G.P. Pazzi, P.
[6] [7] [8] [9] [10] [11] [12]
[13]
275
Polato, C. Susini, A. Vedda, G. Zanella, R. Zannoni, J. Lumin. 87&89 (2000) 673. M. Bettinelli, G. Ingletto, P. Polato, G. Pozza, G. Zanella, R. Zannoni, Phys. Chem. Glasses 37 (1) (1996) 4. S. Brollo, G. Zanella, R. Zannoni, NIMA 293 (1990) 601. G. Zanella, R. Zannoni, R. DallÕIgna, B. Locardi, P. Polato, M. Bettinelli, A. Marigo, NIMA 345 (1994) 198. G. Zanella, R. Zannoni, NIMA 302 (1991) 352. C. Angelini, G. Zanella, R. Zannoni, NIMA 281 (1989) 50. H. Ebendorff Heidepriem, D. Ehrt, Opt. Mater. 15 (2000) 7. H. Ebendorff Heidepriem, D. Ehrt, in: Glass Science and Technology for the 21th century––5th ESG Conference, Prague, June 1999, p. C1-62. M. Nikl, S. Baccaro, A. Cecilia, P. Fabeni, M. Martini, E. Mihokova, K. Nitsch, G.P. Pazzi, N. Solovieva, A. Vedda, in: 7th International Conference on Advanced Technology and Particle Physics, Villa Olmo, Como, Italy, 15–19 October 2001.