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Luminescence properties and radiation response of sodium borate glasses scintillators
Radiation Measurements 55 (2013) 124e127
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Luminescence properties and radiation response of sodium borate glasses scintillators Yutaka Fujimoto a, *, Takayuki Yanagida b, Shingo Wakahara a, Shotaro Suzuki a, Shunsuke Kurosawa a, Akira Yoshikawa a, c a b c
IMR, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan Kyushu Institute of Technology, 2-4, Hibikino, Wakamatsu-ku, Kitakyushu 808-0196, Japan NICHe, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
h i g h l i g h t s < This study is development of new borate glass scintillators. < The glasses showed more than 80% transparency for emission wavelength range. < Visible emission bands were observed under photo-excitation from the glasses. < Cuþ-doped glass demonstrated the highest scintillation output in the glasses.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 March 2012 Received in revised form 20 September 2012 Accepted 18 January 2013
We examined basic luminescence properties and radiation response of sodium borate glass scintillators activated with Pb2þ, Cuþ, Ti4þ, V5þ, W6þ and Yb3þ ions, respectively. These glasses had more than 80% transparency for emission wavelength range, and strong absorption bands due to the charge transition of the ions were observed. In the photoluminescence spectra, all glasses demonstrated intense emission peak in visible region, which are corresponding to the ions with s2 (Pb2þ), d10 (Cuþ) and d0 (Ti4þ, V5þ, W6þ) configuration. Additionally charge transfer emission was observed in Yb3þ-doped glass. When 241Am 5.5 MeV alpha-ray excited the glasses, they showed weak emission intensity because of low energy transfer efficiency from host lattice to emission center. By 241Am irradiated pulse height spectra, Cuþ-doped glass demonstrated the highest scintillation output in the glasses. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Scintillators Sodium borate Glass Luminescence
1. Introduction There is an increasing amount of interest in amorphous materials for optical devise and radiation detector applications, e.g., phosphors, active laser medium, photochromatic lens for sun protection, amplifier device, dosimeter, and scintillator. Compared with bulk crystalline materials, the glasses possess specific advantages such as easy fabrication, low cost, high mechanical strength, and high chemical durability. Fluoride, phosphate, and silicate glasses with high UV transmission and high purity doped with active luminescence center ions were much investigated. Especially, lithium silicate glasses activated with Ce3þ are known to be scintillation material for thermal neutron detection (Ginther and Shulman, 1958), and at present, it are under intense study for
* Corresponding author. Tel.: þ81 22 215 2214; fax: þ81 22 215 2215. E-mail address: [email protected] (Y. Fujimoto). 1350-4487/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2013.01.017
alternative detector of 3He gas counter because 3He gas resources became strictly limited as a result of excessive demand for security applications (Kouzes, 2009). The silicate glasses shows large capture cross section to thermal neutron with 6Li isotope, meanwhile it has a high sensitivity for gamma-ray background. Thus despite the performance of 6Li-loaded silicate glass as scintillator has been studied for a long time, number of report about borate based glasses scintillator for thermal neutron detection are small. Borate glass scintillator are expected to be the high thermal neutron detection efficiency because 10B have a larger high cross section to thermal neutrons than 6Li, and it releases high energy secondary charged particles per absorbed neutron based on 10B(n, a)7Li reactions (van Eijk, 2004). Previously the only related reports were Li2OeB2O3, and Al2O3eNa2OeB2O3eSiO2 based host glass (Ishii et al., 2005; Zadneprovski et al., 2005; Bollinger, 1962). In this work, we developed sodium tetraborate Na2B4O7 glass scintillators doped with several luminescence centers, such as the ions with s2 (Pb2þ, Bi3þ) and d0 (Ti4þ, V5þ, W6þ) configurations
Y. Fujimoto et al. / Radiation Measurements 55 (2013) 124e127
125
because they yield intense emission bands in blue-green wavelength range in other glass host (Blasse and Grabmaier, 1994). Additionally the Yb3þ-doped glass was also examined with hope for emission from charge transfer state of Yb3þ that shows fast response by thermal quenching (Antonini et al., 2001). The luminescence properties and radiation response of the glasses were studied by the measurements of photo- and radio-luminescence spectra, and 241Am irradiated pulse height spectra. 2. Experimental procedures and results 2.1. Preparation of sodium tetraborate glass Na2B4O7 (5N), PbO (4N), CuO (4N), TiO2 (4N), V2O5 (4N), WO3 (4N) and Yb2O3 (5N) high purity powders were used as starting materials for the insert of glass samples. The concentration of dopants is 1 mol % for the luminescence center. The mixture was loaded into Pt container and then it was melted at 1100 C in air atmosphere. Finally it was cooled as a faster rate to obtain the glass samples with required composition. By the process, transparency glass to evaluate optical and scintillation properties were obtained (see Fig. 1). The vitreous phase of the samples was checked by X-ray diffraction (XRD) using a RINT2000 diffractometer (RIGAKU). The X-ray source was CuKa with accelerating voltage of 40 kV, and the tube current of 40 mA. The measurement was carried out in the 2q range from 5 to 80 at room temperature. Fig. 2 shows the obtained XRD pattern of undoped sample. The pattern showed just three broad peaks at about 20 , 30 and 47, thus we confirmed that it formed a typical amorphous phase. Similar result was observed in the case of those of glasses with several luminescence center ions. 2.2. Optical transmittance, photoluminescence and decay time Transmittance spectra of the polished glasses with thickness of 1.0 mm were evaluated using V530 UV/VIS spectrophotometer (Jasco) at wavelength range from 190 to 900 nm. The results are shown in Fig. 3. From the spectra, the samples showed high transparency and strong absorption bands due to the doped ions which are Pb2þ (w280 nm), Cuþ/Cu2þ (w300 nm, 600e900 nm), Ti3þ/Ti4þ (w300 nm), V5þ (w350 nm), W6þ (w250 nm) and Yb3þ (w230 nm), respectively. Examining the luminescence properties, we measured the excitation and emission spectra by FLS920 spectrometer (Edinburgh Instruments Ltd.) equipped with a Xe-arc lamp as a light source. In addition, the decay times were checked using the similar spectrometer, nanosecond- and microsecondflash lamp. The calculated decay times are obtained with the exponential function fitting and its deconvolution with the instrumental response. The result of Pb-, Cu-, Ti-, V-, W- and Ybdoped glasses are presented in Figs. 4e9. Pb-doped sample showed a strong luminescence around 380 nm upon excitation at 285 nm as shown in Fig. 4. The ultraviolet-bluish luminescence was assigned to the transition from the 3P1 excited state level to the 1S0 ground state (Pekgözlü and Karabulut, 2009). The excitation peak of Pbdoped crystals were observed 285 nm, which was caused by the 1 S0e3P1 transitions of Pb2þ ion. The decay curve under excitation at
Fig. 1. As prepared undoped sodium tetraborate glasses.
Fig. 2. XRD pattern of as prepared undoped sodium tetraborate glass.
260 nm yielded relatively shorter decay time of about 410 ns. In the spectra of Cu-doped sample, it exhibit blue luminescence around 450 nm under excited at both 270 nm, as shown in Fig. 5. This is cause by the transition between 3d94s and 3 d10 of Cuþ (Blasse and Grabmaier, 1994). From the result of decay time measurement, the value of decay component was about 28.5 ms. Fig. 6 illustrated the result of Ti-doped sample, the charge transfer emission between Ti4þeTi3 was observed around 400e500 nm under excited at both 275 and 330 nm (Blasse and Grabmaier, 1994). The decay time of charge transfer emission was determined to be about 86 and 1030 ms. The emission spectra of V-doped sample were measured under 340 nm excitation as it is presented in Fig. 7. Broad luminescence band was observed around 500 nm due to the transition from triplet state of VO3 4 (Oka et al., 2006; Yang et al., 2005) under 340 nm excitation. The values of the decay component were calculated to be approximately 40 ms. W-doped sample showed bluegreen luminescence corresponding to charge transfer transition at the oxyanion complex, the (WO4)2 in scheelite and (WO6)6 in wolframite structure (Blasse and Schipper, 1974), as illustrated in Fig. 8. By the emission decay curve, the decay constant found to be about 32 and 130 ms. In the case of those of Yb-doped sample, ultraviolet luminescence peaking around 370 and 460 nm caused by the transition from charge transfer state to the 2F5/2 and 2F7/2 level of Yb3þ (Antonini et al., 2001) was observed under excited at 265 nm (see Fig. 9). The fast decay time was calculated to be about 390 ns. Thus we confirmed the intense fluorescence from all sodium tetraborate glasses by photo-excitation. 2.3. Radioluminescence and pulse height spectra According to the results of photo-excitation, we demonstrated the alpha excited radioluminescence spectra which replaces for the
Fig. 3. Transmittance of Pb-, Cu-, Ti-, V-, W-, and Yb-doped sodium tetraborate glasses.
126
Y. Fujimoto et al. / Radiation Measurements 55 (2013) 124e127
Fig. 4. Photoluminescence and decay curve of Pb-doped sodium tetraborate glasses. Fig. 7. Photoluminescence and decay curve of V-doped sodium tetraborate glasses.
Fig. 5. Photoluminescence and decay curve of Cu-doped sodium tetraborate glasses.
Fig. 8. Photoluminescence and decay curve of W-doped sodium tetraborate glasses.
B(n, a)7Li reactions. In the measurement, the FLS920 spectrometer and 241Am sealed radiation source were used as a detector and alpha source. The glass samples were placed directly on the sealed source, and the fluorescence from the samples is detected by the spectrometer. The spectra are represented in Fig. 10. Unlike the measurement of those of photo-excitation, the emission intensity seemed very poor. It can be related to low energy transfer efficiency from host glass to emission centers caused by some kind of trapped state. The structural defects can be for example the oxygen vacancies and cation vacancies as acting electron and hole traps. Further investigation will be required for a better understanding of this problem. From the spectra, we concluded that Cu-doped glass showed highest emission intensity in our sample.
Finally, 241Am alpha-ray irradiated pulse height spectra were measured in order to compare the scintillation light yield. The measurement setup is illustrated in Fig. 10. These samples were mounted on a window of photomultiplier tube (PMT, Hamamatsu R7600U) with optical silicon grease (OKEN 6262A), converted by a Teflon tape and irradiated by a 241Am alpha-ray source. The pulse signals were processed using a pre-amplifier (ORTEC 113), a shaping amplifier (ORTEC 572), a multichannel analyzer (Amptec Pocket MCA 8000A), and finally to a personal computer for analysis. The shaping time was 10e100 ms for our samples as an optimum value. The alpha-ray peak channels were determined with fitting by a single Gaussian function. The results are presented in Fig. 11. Although the Yb- and Cu-doped glass samples exhibited alpha-ray peak at approximately 50 ch and 145 ch, the peak from those of
Fig. 6. Photoluminescence and decay curve of Ti-doped sodium tetraborate glasses.
Fig. 9. Photoluminescence and decay curve of Yb-doped sodium tetraborate glasses.
10
Y. Fujimoto et al. / Radiation Measurements 55 (2013) 124e127
Fig. 10. 241Am a-ray excited radioluminescence spectra of undoped, Pb-, Cu-, Ti-, V-, W-, and Yb-doped sodium tetraborate glasses.
127
transmittance spectra, strong absorption bands due to the charge transition of the doped ions were observed in visible wavelength region. All glasses showed intense emission bands, which are corresponding to the various types of charge transitions of doped ions. When 241Am 5.5 MeV alpha-ray excited the glasses, they showed weak emission intensity because of low energy transfer efficiency from host lattice to emission center. By 241Am irradiated pulse height spectra, Cuþ-doped glass demonstrated the highest scintillation output in our glasses. In this study, although we didn’t obtained desired results with high light yield for new borate glasses, we have not made an attempt an evaluation for optimization of dopant concentration and other dopants such as Bi3þ, Agþ, Mo6þ, Zr4þ and so on. Therefore we would like to investigate luminescence and scintillation properties for these glasses in order to develop new alternative glass scintillators.
References
Fig. 11. 241Am a-ray irradiated pulse height spectra of undoped, Yb-, V-, Ti-, and Cudoped sodium tetraborate glasses.
other samples were not detect because of low light yield. These results consist with those of radioluminescence measurement. 3. Summary We studied basic photo- and radio-luminescence properties and scintillation light yield of sodium borate glass scintillators activated with Pb2þ, Cuþ, Ti4þ, V5þ, W6þ and Yb3þ ions, respectively. In
Antonini, P., Bressi, G., Carugno, G., Iannuzzi, D., 2001. Scintillation properties of YAG: Yb crystals. Nucl. Instr. Meth. A 460, 469e471. Blasse, G., Grabmaier, B.C., 1994. Luminescencent Materials. Springer-Verlag, Berlin, Heidelberg. Blasse, G., Schipper, W.J., 1974. Low-temperature photoluminescence of strontium and barium tungstate. Phys. Stat. Sol. A 25, K163eK165. Bollinger, L.M., 1962. Glass scintillators for neutron detection. Nucl. Instr. Meth. 17, 97e116. Ginther, R.J., Shulman, J.H., 1958. Glass scintillators. IRE Trans. Nucl. Sci. NS-5, 92e95. Ishii, M., Kuwano, Y., Asai, T., Asaba, S., Kawamura, M., Senguttuvan, N., Hayashi, T., Kobayashi, M., Nikl, M., Hosoya, S., Sakai, K., Adachi, T., Oku, T., Shimizu, H.M., 2005. Boron based oxide scintillation glass for neutron detection. Nucl. Instrum. Meth. A 537, 282e285. Kouzes, R.T., 2009. The 3He Supply Problem. Pacific Northwest National Laboratory, Richland, WA. Technical Rpt. PNNL-18388. Oka, K., Unoki, H., Shibata, H., Eisaki, H., 2006. Crystal growth of rare-earth orthovanadate (RVO4) by the floating-zone method. J. Cryst. Growth 286, 288e293. Pekgözlü, I., Karabulut, H., 2009. Synthesis and photoluminescence of Pb2þ doped SrB2O4. Inorg. Mater. 45, 61e64. van Eijk, C.W.E., 2004. Radiat. Meas. 38, 337e342. Yang, L., Wang, C., Dong, Y., Da, N., Hu, X., Chen, D., Qiu, J., 2005. Three-photonexcited upconversion luminescence of YVO4 single crystal by infrared femtosecond laser irradiation. Opt. Express 13, 10157e10162. Zadneprovski, B.I., Eremin, N.V., Paskhalov, A.A., 2005. New inorganic scintillators on the basis of LBO glass for neutron registration. Func. Mate. 12, 261e268.
Contents lists available at SciVerse ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Luminescence properties and radiation response of sodium borate glasses scintillators Yutaka Fujimoto a, *, Takayuki Yanagida b, Shingo Wakahara a, Shotaro Suzuki a, Shunsuke Kurosawa a, Akira Yoshikawa a, c a b c
IMR, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan Kyushu Institute of Technology, 2-4, Hibikino, Wakamatsu-ku, Kitakyushu 808-0196, Japan NICHe, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
h i g h l i g h t s < This study is development of new borate glass scintillators. < The glasses showed more than 80% transparency for emission wavelength range. < Visible emission bands were observed under photo-excitation from the glasses. < Cuþ-doped glass demonstrated the highest scintillation output in the glasses.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 31 March 2012 Received in revised form 20 September 2012 Accepted 18 January 2013
We examined basic luminescence properties and radiation response of sodium borate glass scintillators activated with Pb2þ, Cuþ, Ti4þ, V5þ, W6þ and Yb3þ ions, respectively. These glasses had more than 80% transparency for emission wavelength range, and strong absorption bands due to the charge transition of the ions were observed. In the photoluminescence spectra, all glasses demonstrated intense emission peak in visible region, which are corresponding to the ions with s2 (Pb2þ), d10 (Cuþ) and d0 (Ti4þ, V5þ, W6þ) configuration. Additionally charge transfer emission was observed in Yb3þ-doped glass. When 241Am 5.5 MeV alpha-ray excited the glasses, they showed weak emission intensity because of low energy transfer efficiency from host lattice to emission center. By 241Am irradiated pulse height spectra, Cuþ-doped glass demonstrated the highest scintillation output in the glasses. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Scintillators Sodium borate Glass Luminescence
1. Introduction There is an increasing amount of interest in amorphous materials for optical devise and radiation detector applications, e.g., phosphors, active laser medium, photochromatic lens for sun protection, amplifier device, dosimeter, and scintillator. Compared with bulk crystalline materials, the glasses possess specific advantages such as easy fabrication, low cost, high mechanical strength, and high chemical durability. Fluoride, phosphate, and silicate glasses with high UV transmission and high purity doped with active luminescence center ions were much investigated. Especially, lithium silicate glasses activated with Ce3þ are known to be scintillation material for thermal neutron detection (Ginther and Shulman, 1958), and at present, it are under intense study for
* Corresponding author. Tel.: þ81 22 215 2214; fax: þ81 22 215 2215. E-mail address: [email protected] (Y. Fujimoto). 1350-4487/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radmeas.2013.01.017
alternative detector of 3He gas counter because 3He gas resources became strictly limited as a result of excessive demand for security applications (Kouzes, 2009). The silicate glasses shows large capture cross section to thermal neutron with 6Li isotope, meanwhile it has a high sensitivity for gamma-ray background. Thus despite the performance of 6Li-loaded silicate glass as scintillator has been studied for a long time, number of report about borate based glasses scintillator for thermal neutron detection are small. Borate glass scintillator are expected to be the high thermal neutron detection efficiency because 10B have a larger high cross section to thermal neutrons than 6Li, and it releases high energy secondary charged particles per absorbed neutron based on 10B(n, a)7Li reactions (van Eijk, 2004). Previously the only related reports were Li2OeB2O3, and Al2O3eNa2OeB2O3eSiO2 based host glass (Ishii et al., 2005; Zadneprovski et al., 2005; Bollinger, 1962). In this work, we developed sodium tetraborate Na2B4O7 glass scintillators doped with several luminescence centers, such as the ions with s2 (Pb2þ, Bi3þ) and d0 (Ti4þ, V5þ, W6þ) configurations
Y. Fujimoto et al. / Radiation Measurements 55 (2013) 124e127
125
because they yield intense emission bands in blue-green wavelength range in other glass host (Blasse and Grabmaier, 1994). Additionally the Yb3þ-doped glass was also examined with hope for emission from charge transfer state of Yb3þ that shows fast response by thermal quenching (Antonini et al., 2001). The luminescence properties and radiation response of the glasses were studied by the measurements of photo- and radio-luminescence spectra, and 241Am irradiated pulse height spectra. 2. Experimental procedures and results 2.1. Preparation of sodium tetraborate glass Na2B4O7 (5N), PbO (4N), CuO (4N), TiO2 (4N), V2O5 (4N), WO3 (4N) and Yb2O3 (5N) high purity powders were used as starting materials for the insert of glass samples. The concentration of dopants is 1 mol % for the luminescence center. The mixture was loaded into Pt container and then it was melted at 1100 C in air atmosphere. Finally it was cooled as a faster rate to obtain the glass samples with required composition. By the process, transparency glass to evaluate optical and scintillation properties were obtained (see Fig. 1). The vitreous phase of the samples was checked by X-ray diffraction (XRD) using a RINT2000 diffractometer (RIGAKU). The X-ray source was CuKa with accelerating voltage of 40 kV, and the tube current of 40 mA. The measurement was carried out in the 2q range from 5 to 80 at room temperature. Fig. 2 shows the obtained XRD pattern of undoped sample. The pattern showed just three broad peaks at about 20 , 30 and 47, thus we confirmed that it formed a typical amorphous phase. Similar result was observed in the case of those of glasses with several luminescence center ions. 2.2. Optical transmittance, photoluminescence and decay time Transmittance spectra of the polished glasses with thickness of 1.0 mm were evaluated using V530 UV/VIS spectrophotometer (Jasco) at wavelength range from 190 to 900 nm. The results are shown in Fig. 3. From the spectra, the samples showed high transparency and strong absorption bands due to the doped ions which are Pb2þ (w280 nm), Cuþ/Cu2þ (w300 nm, 600e900 nm), Ti3þ/Ti4þ (w300 nm), V5þ (w350 nm), W6þ (w250 nm) and Yb3þ (w230 nm), respectively. Examining the luminescence properties, we measured the excitation and emission spectra by FLS920 spectrometer (Edinburgh Instruments Ltd.) equipped with a Xe-arc lamp as a light source. In addition, the decay times were checked using the similar spectrometer, nanosecond- and microsecondflash lamp. The calculated decay times are obtained with the exponential function fitting and its deconvolution with the instrumental response. The result of Pb-, Cu-, Ti-, V-, W- and Ybdoped glasses are presented in Figs. 4e9. Pb-doped sample showed a strong luminescence around 380 nm upon excitation at 285 nm as shown in Fig. 4. The ultraviolet-bluish luminescence was assigned to the transition from the 3P1 excited state level to the 1S0 ground state (Pekgözlü and Karabulut, 2009). The excitation peak of Pbdoped crystals were observed 285 nm, which was caused by the 1 S0e3P1 transitions of Pb2þ ion. The decay curve under excitation at
Fig. 1. As prepared undoped sodium tetraborate glasses.
Fig. 2. XRD pattern of as prepared undoped sodium tetraborate glass.
260 nm yielded relatively shorter decay time of about 410 ns. In the spectra of Cu-doped sample, it exhibit blue luminescence around 450 nm under excited at both 270 nm, as shown in Fig. 5. This is cause by the transition between 3d94s and 3 d10 of Cuþ (Blasse and Grabmaier, 1994). From the result of decay time measurement, the value of decay component was about 28.5 ms. Fig. 6 illustrated the result of Ti-doped sample, the charge transfer emission between Ti4þeTi3 was observed around 400e500 nm under excited at both 275 and 330 nm (Blasse and Grabmaier, 1994). The decay time of charge transfer emission was determined to be about 86 and 1030 ms. The emission spectra of V-doped sample were measured under 340 nm excitation as it is presented in Fig. 7. Broad luminescence band was observed around 500 nm due to the transition from triplet state of VO3 4 (Oka et al., 2006; Yang et al., 2005) under 340 nm excitation. The values of the decay component were calculated to be approximately 40 ms. W-doped sample showed bluegreen luminescence corresponding to charge transfer transition at the oxyanion complex, the (WO4)2 in scheelite and (WO6)6 in wolframite structure (Blasse and Schipper, 1974), as illustrated in Fig. 8. By the emission decay curve, the decay constant found to be about 32 and 130 ms. In the case of those of Yb-doped sample, ultraviolet luminescence peaking around 370 and 460 nm caused by the transition from charge transfer state to the 2F5/2 and 2F7/2 level of Yb3þ (Antonini et al., 2001) was observed under excited at 265 nm (see Fig. 9). The fast decay time was calculated to be about 390 ns. Thus we confirmed the intense fluorescence from all sodium tetraborate glasses by photo-excitation. 2.3. Radioluminescence and pulse height spectra According to the results of photo-excitation, we demonstrated the alpha excited radioluminescence spectra which replaces for the
Fig. 3. Transmittance of Pb-, Cu-, Ti-, V-, W-, and Yb-doped sodium tetraborate glasses.
126
Y. Fujimoto et al. / Radiation Measurements 55 (2013) 124e127
Fig. 4. Photoluminescence and decay curve of Pb-doped sodium tetraborate glasses. Fig. 7. Photoluminescence and decay curve of V-doped sodium tetraborate glasses.
Fig. 5. Photoluminescence and decay curve of Cu-doped sodium tetraborate glasses.
Fig. 8. Photoluminescence and decay curve of W-doped sodium tetraborate glasses.
B(n, a)7Li reactions. In the measurement, the FLS920 spectrometer and 241Am sealed radiation source were used as a detector and alpha source. The glass samples were placed directly on the sealed source, and the fluorescence from the samples is detected by the spectrometer. The spectra are represented in Fig. 10. Unlike the measurement of those of photo-excitation, the emission intensity seemed very poor. It can be related to low energy transfer efficiency from host glass to emission centers caused by some kind of trapped state. The structural defects can be for example the oxygen vacancies and cation vacancies as acting electron and hole traps. Further investigation will be required for a better understanding of this problem. From the spectra, we concluded that Cu-doped glass showed highest emission intensity in our sample.
Finally, 241Am alpha-ray irradiated pulse height spectra were measured in order to compare the scintillation light yield. The measurement setup is illustrated in Fig. 10. These samples were mounted on a window of photomultiplier tube (PMT, Hamamatsu R7600U) with optical silicon grease (OKEN 6262A), converted by a Teflon tape and irradiated by a 241Am alpha-ray source. The pulse signals were processed using a pre-amplifier (ORTEC 113), a shaping amplifier (ORTEC 572), a multichannel analyzer (Amptec Pocket MCA 8000A), and finally to a personal computer for analysis. The shaping time was 10e100 ms for our samples as an optimum value. The alpha-ray peak channels were determined with fitting by a single Gaussian function. The results are presented in Fig. 11. Although the Yb- and Cu-doped glass samples exhibited alpha-ray peak at approximately 50 ch and 145 ch, the peak from those of
Fig. 6. Photoluminescence and decay curve of Ti-doped sodium tetraborate glasses.
Fig. 9. Photoluminescence and decay curve of Yb-doped sodium tetraborate glasses.
10
Y. Fujimoto et al. / Radiation Measurements 55 (2013) 124e127
Fig. 10. 241Am a-ray excited radioluminescence spectra of undoped, Pb-, Cu-, Ti-, V-, W-, and Yb-doped sodium tetraborate glasses.
127
transmittance spectra, strong absorption bands due to the charge transition of the doped ions were observed in visible wavelength region. All glasses showed intense emission bands, which are corresponding to the various types of charge transitions of doped ions. When 241Am 5.5 MeV alpha-ray excited the glasses, they showed weak emission intensity because of low energy transfer efficiency from host lattice to emission center. By 241Am irradiated pulse height spectra, Cuþ-doped glass demonstrated the highest scintillation output in our glasses. In this study, although we didn’t obtained desired results with high light yield for new borate glasses, we have not made an attempt an evaluation for optimization of dopant concentration and other dopants such as Bi3þ, Agþ, Mo6þ, Zr4þ and so on. Therefore we would like to investigate luminescence and scintillation properties for these glasses in order to develop new alternative glass scintillators.
References
Fig. 11. 241Am a-ray irradiated pulse height spectra of undoped, Yb-, V-, Ti-, and Cudoped sodium tetraborate glasses.
other samples were not detect because of low light yield. These results consist with those of radioluminescence measurement. 3. Summary We studied basic photo- and radio-luminescence properties and scintillation light yield of sodium borate glass scintillators activated with Pb2þ, Cuþ, Ti4þ, V5þ, W6þ and Yb3þ ions, respectively. In
Antonini, P., Bressi, G., Carugno, G., Iannuzzi, D., 2001. Scintillation properties of YAG: Yb crystals. Nucl. Instr. Meth. A 460, 469e471. Blasse, G., Grabmaier, B.C., 1994. Luminescencent Materials. Springer-Verlag, Berlin, Heidelberg. Blasse, G., Schipper, W.J., 1974. Low-temperature photoluminescence of strontium and barium tungstate. Phys. Stat. Sol. A 25, K163eK165. Bollinger, L.M., 1962. Glass scintillators for neutron detection. Nucl. Instr. Meth. 17, 97e116. Ginther, R.J., Shulman, J.H., 1958. Glass scintillators. IRE Trans. Nucl. Sci. NS-5, 92e95. Ishii, M., Kuwano, Y., Asai, T., Asaba, S., Kawamura, M., Senguttuvan, N., Hayashi, T., Kobayashi, M., Nikl, M., Hosoya, S., Sakai, K., Adachi, T., Oku, T., Shimizu, H.M., 2005. Boron based oxide scintillation glass for neutron detection. Nucl. Instrum. Meth. A 537, 282e285. Kouzes, R.T., 2009. The 3He Supply Problem. Pacific Northwest National Laboratory, Richland, WA. Technical Rpt. PNNL-18388. Oka, K., Unoki, H., Shibata, H., Eisaki, H., 2006. Crystal growth of rare-earth orthovanadate (RVO4) by the floating-zone method. J. Cryst. Growth 286, 288e293. Pekgözlü, I., Karabulut, H., 2009. Synthesis and photoluminescence of Pb2þ doped SrB2O4. Inorg. Mater. 45, 61e64. van Eijk, C.W.E., 2004. Radiat. Meas. 38, 337e342. Yang, L., Wang, C., Dong, Y., Da, N., Hu, X., Chen, D., Qiu, J., 2005. Three-photonexcited upconversion luminescence of YVO4 single crystal by infrared femtosecond laser irradiation. Opt. Express 13, 10157e10162. Zadneprovski, B.I., Eremin, N.V., Paskhalov, A.A., 2005. New inorganic scintillators on the basis of LBO glass for neutron registration. Func. Mate. 12, 261e268.