- Email: [email protected]
Photoluminescence, photo-stimulated luminescence and thermoluminescence properties of CaB2O4 crystals activated with Ce3+
Optical Materials 41 (2015) 49–52
Contents lists available at ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Photoluminescence, photo-stimulated luminescence and thermoluminescence properties of CaB2O4 crystals activated with Ce3+ Yutaka Fujimoto a,⇑, Takayuki Yanagida b, Masanori Koshimizu a, Keisuke Asai a a b
Tohoku University, 6-6-04, Aramaki Aza Aoba Aoba-ku, Sendai, Miyagi 980-8579, Japan Kyushu Institute of Technology, 2-4, Hibikino, Wakamatsu-ku, Kitakyushu, Fukuoka 808-0196, Japan
a r t i c l e
i n f o
Article history: Available online 29 December 2014 Keywords: Photo-stimulated luminescence Thermoluminescence Ce3+ 5d–4f transition
a b s t r a c t Photoluminescence (PL), photo-stimulated luminescence (PSL), and thermoluminescence (TL) properties of a Ce-doped CaB2O4 crystal were studied. The Ce-doped crystal was prepared by the simple solidification method using a Pt crucible under nitrogen atmosphere. A PL emission band in the 350–370 nm wavelength range was obtained under excitation at 325 nm owing to the 5d (t2g)–4f (2F5/2, 2F7/2)-allowed transition of the Ce3+ emission center. The fluorescence quantum efficiency and the decay time of Ce3+ were estimated to be about 70% and 29 ns, respectively. The 5d–4f emission band of Ce3+ also appeared in the 350–370 nm wavelength range in the TL and PSL spectra. Good linear TL and PSL responses were observed in the 1–1000 mGy and 1–10,000 mGy X-ray dose range, respectively. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Photo-stimulated luminescence (PSL) and thermoluminescence (TL) exhibited by inorganic crystals and glasses irradiated with X-rays, gamma-rays, and neutrons are interesting phenomena, both from the fundamental as well as practical viewpoints. The ionizing radiation leaves the host material in a metastable state, which is characterized by the electrons and holes separately trapped at defects in the host matrix. During the PSL and TL processes, visible light and heat stimulates the release of the electrons and holes from these trapping centers, resulting in electron–hole recombination and the excitation of emission centers in the host material. Many studies have been conducted to better understand the detailed mechanism of PSL and TL and to apply these phenomena to materials for radiation dosimetry. After a great deal of effort, BaFBr:Eu [1,2], LiF:Mg, Cu, P [3,4] and Al2O3:C [5,6] are now available for use as imaging plates and personal dosimeters. Recently, the PSL and TL properties of borate based phosphors have been reported because of their good tissue equivalence and excellent sensitivity to X-rays, gamma-rays, and neutrons. Among the borate-based phosphors, the use of alkali-earth tetra-borate crystals (such as MgB4O7, CaB4O7, and SrB4O7) activated with rare-earth and transition-metal ions as the TL material has been investigated by several researchers [7–12]. Our group has studied the PSL and TL properties of other types of alkali-earth borate ⇑ Corresponding author. Tel.: +81 22 795 7219. E-mail address: [email protected] (Y. Fujimoto). http://dx.doi.org/10.1016/j.optmat.2014.11.049 0925-3467/Ó 2014 Elsevier B.V. All rights reserved.
crystals in recent years. The present study focuses on calcium meta-borate (CaB2O4) crystals. We selected this compound because its chemical composition is similar to that of CaB4O7, which has demonstrated intense emission owing to lattice defects and rare-earth ionic dopants [13–15]. To the best of our knowledge, no other observations on both PSL and TL from CaB2O4 crystal activated with Ce3+ have been reported so far. In this communication, the basic PL, PSL, and TL properties of Ce3+:CaB2O4 crystals are reported and discussed.
2. Experimental procedures The Ce3+:CaB2O4 crystal sample was grown by the simple solidification method. The starting materials were prepared from a stoichiometric mixture of CaCO3 (4N), H3BO3 (4N), and CeO2 (4N) powders. The Ce concentration was 0.5% (nominal composition) and the mixed powders were placed in a Pt crucible (50 mm in both diameter and height). The crucibles were set in the electric furnace and enclosed by the MoSi2 resist heater. The crucible was heated up to 1160 °C (the melting point of CaB2O4) and maintained at this temperature for about 10 h under a nitrogen atmosphere. The furnace was then cooled to room temperature at a cooling rate of 1 °C/min. The transmittance spectrum of the Ce-doped crystal was recorded in the 190–2700 nm wavelength regime with a JASCO V-670 spectrometer. The spectrometer was equipped with a photomultiplier tube (PMT) and a Peltier-cooled PbS detector for use in the UV–VIS and the NIR–IR regions, respectively. The light sources for both the regions were deuterium and halogen lamps.
50
Y. Fujimoto et al. / Optical Materials 41 (2015) 49–52
To determine the basic luminescence properties of Ce3+, we demonstrated the photoluminescence (PL) map using a Quantaurus-QY system (Hamamatsu). This system consists of a Xe-lamp, a monochromator, an integrating sphere, a multichannel detector, and a personal computer. The fluorescence quantum efficiency (QE) of Ce3+ at room temperature was calculated using the difference between the number of photons emitted from a sample and the number of photons absorbed by a sample using an integrating sphere. The TL glow curve of the Ce3+-doped crystal was measured in air with a TL-2000 reader manufactured by Nanogray Inc. A linear heating rate of 1 K s 1 was used to record the glow curves, and the TL intensities were recorded in the temperature range 320– 700 K. An original X-ray generator (XRB80P Monoblock, Spellman) equipped with a tungsten target was used as the irradiation source. The generator was supplied with a voltage of 40 kV and current in the range 0.5–5 mA. X-ray irradiation doses of 1, 10, 100, and 1000 mGy were chosen for the measurements. After the measurements, the sample was annealed at 800 K with each cycle as a reset process. The TL spectrum of the Ce3+-doped crystal was evaluated with a SR163i-UV spectrometer combined with a DU920P CCD detector (Andor). The TL photons emitted from the sample were sent to the spectrometer using an optical fiber to avoid direct heating. After irradiation of the sample with 1000 mGy, the spectra under thermo-stimulated condition were recorded at 360 K. The integration time for this experiment was 20 s. The PSL properties of the Ce3+-doped crystal were examined using a Quantaurus-Tau (Hamamatsu Photonics Co.) fluorophotometer. A light-emitting diode (LED) wavelength of 630 nm was used as the optimum stimulation light, and the X-ray irradiation doses were 1, 10, 100, 1000, and 10,000 mGy. The PSL spectra were recorded at room temperature.
Fig. 2. Optical transmittance spectrum of the Ce-doped crystal in the UV–NIR wavelength region.
3. Results and discussions The Ce3+-doped crystal obtained was clear and colorless, with cleavage cracks observed, as shown in Fig. 1. Previous studies have reported that the cracks arise owing to the (B2O4)n2n layers parallel to the c-axis in the CaB2O4 lattice [16–18]. Fig. 2 illustrates the transmittance spectrum of the Ce3+-doped crystal. In the spectrum, the absorption bands appeared in the 230–325 nm wavelength region owing to the allowed transition from the 4f ground state to the 5d excited states (t2g, e2g) of Ce3+. In the 350–2700 nm wavelength range, the crystal showed no absorption lines and exhibited high transmittance of more than 75%. In the PL map (Fig. 3), an intense emission band was observed in the 350–370 nm wavelength range, when light at 325 nm excited the crystal. The ultraviolet emission band is assigned to the transition from the Ce3+5d (t2g) state to the 4f ground-state levels
Fig. 1. View of the as grown Ce (0.5%)-doped CaB2O4 crystal.
Fig. 3. PL map of the Ce-doped crystal at room temperature.
(2F5/2 and 2F7/2). The fluorescence QE for the emission was approximately 70%. The emission wavelength in the case of Ce3+:CaB2O4 was short compared to commercial oxide phosphors activated with Ce3+ such as Ce3+:Y3Al5O12, Ce3+:Gd2SiO5, Ce3+:L2SiO5, and Ce3+:Gd3Al2Ga3O12 [19–23]. This can be considered to be a result of the influence of the host crystal lattice on the splitting of 5d levels of Ce3+, because the 5d levels are significantly affected by the ligand field of the first coordination sphere [24]. Fig. 4 shows the TL glow curve of the Ce3+-doped (a) and undoped (b) crystals irradiated with 1000 mGy X-rays. In the case of the Ce3+-doped crystal, an intense glow peak at 360 K was observed, while the TL glow curve for the undoped crystal showed three peaks at 425 K, 510 K, and 610 K. The glow peaks of the undoped crystal are associated with the intrinsic electron trap centers caused by various lattice defects in the host lattice. The glow peak at 360 K for the Ce3+-doped crystal may be due to other charged point defects such as oxygen vacancies or calcium vacancies because it is expected that Ce3+ ion occupy Ca2+ cationic site. Additionally another possible factor is the Ce3+ ion which acts as a hole trap center. The dose dependence of the glow peak intensities is illustrated in Fig. 5. According to the result, the Ce3+-doped crystal was found to exhibit a good linear response in the 1–1000 mGy irradiation dose range. The TL spectra are shown in
Y. Fujimoto et al. / Optical Materials 41 (2015) 49–52
51
Fig. 4. TL glow curves of the Ce-doped crystal (a) compared with the undoped crystal (b).
Fig. 7. PSL spectrum of the Ce-doped crystal under stimulation with 630 nm LED light.
Fig. 5. Dose response of the TL glow peak intensities in the Ce-doped crystal.
Fig. 8. Dose response of the PSL peak intensities of the Ce-doped crystal.
and they recombine through the Ce3+ emission centers by heating stimulation. The PSL spectrum of the Ce3+-doped crystal irradiated with 1000 mGy X-rays is presented in Fig. 7. In the spectrum, an emission band corresponding to Ce3+ was observed in the 350– 370 nm wavelength range, which is consistent with the PL and TL spectra. Thus, it can be concluded that the electrons and holes in the trap centers can be released by visible light stimulation. With our experimental system, a linear PSL response in the dose range 1–10,000 mGy was observed, as shown in Fig. 8. 4. Summary
Fig. 6. TL spectrum of the Ce-doped crystal stimulated by heating to 360 K.
Fig. 6. The spectrum showed an intense emission band in the 350– 370 nm wavelength range, just as in the case of the PL spectrum. It is clear that part of the electrons and holes generated by irradiating the sample with X-rays is trapped in the shallow trap centers in the host crystal. When they are subsequently released from the traps,
The basic PL, PSL, and TL properties of Ce3+-doped CaB2O4 crystal were studied. The PL spectrum obtained by excitation at 325 nm showed an intense emission band in the 350–370 nm wavelength range owing to the transition from the Ce3+5d (t2g) state to the 4f ground-state levels (2F5/2 and 2F7/2). The PL quantum efficiency of Ce3+ was estimated to be about 70%. The TL and PSL spectra also exhibited the Ce3+ 5d–4f emission band in the 350– 370 nm wavelength range when stimulated by heating to 360 K and by exposing to 630 nm-light, respectively. From the result, it follows that the electrons and holes trapped in the shallow traps owing to irradiation by X-rays were released by heating and light stimulation; they subsequently and then they recombined with the holes through the Ce3+ emission centers. The measurement of
52
Y. Fujimoto et al. / Optical Materials 41 (2015) 49–52
the dose response showed good linear TL and PSL responses in the 1–1000 mGy and 1–10,000 mGy ranges, respectively. References [1] K. Takahashi, K. Kohda, J. Miyhara, Y. Kanemitsu, K. Amitani, S. Shionoya, J. Lumin. 31 and 32 (1984) 266. [2] Y. Amemiya, J. Miyhara, Nature 336 (1988) 89. [3] W. Shoushan, C. Goulong, W. Fang, L. Yuanfang, Z. Ziying, Z. Jianhuan, Radiat. Prot. Dosim. 14 (3) (1986) 223. [4] C.M.H. Driscoll, A.F. McWhan, J.B. O’Hagan, J. Dodson, S.J. Mundy, C.D. Todd, Radiat. Prot. Dosim. 17 (1986) 367. [5] B.G. Markey, L.E. Colyott, S.W.S. Mckeever, Radiat. Meas. 24 (1995) 457. [6] S.W.S. McKeever, M.S. Akselrod, B.G. Markey, Radiat. Prot. Dosim. 65 (1996) 267. [7] M. Prokic, Nucl. Instrum. Methods 175 (1980) 83. [8] C. Furetta, M. Prokic, R. Salamon, G. Kitis, Appl. Radiat. Isot. 52 (2) (2000) 243. [9] E. Tekin, A. Ege, T. Karali, P.D. Townsend, M. Proki, Radiat. Meas. 45 (2010) 764. [10] M.E. Haghiri, E. Saion, N. Soltani, W. Wan Abdullah, M. Navasery, M. Hashim, J. Lumin. 141 (2013) 177. [11] M. Santiago, C. Grasseli, E. Caselli, M. Lester, A. Lavat, F. Spano, Phys. Status Solidi A 185 (2001) 285. [12] R.P. Yavetskiy, E.F. Dolzhenkova, A.V. Tolmachev, S.V. Parkhomenko, V.N. Baumer, A.L. Prosvirnin, J. Alloys Compd. 441 (2007) 202.
[13] I.V. Berezovskaya, N.P. Efryushina, A.S. Voloshinovskii, G.B. Stryganyuk, P.V. Pir, V.P. Dotsenko, Radiat. Meas. 42 (2007) 878. [14] Y. Fujimoto, T. Yanagida, N. Kawaguchi, S. Kurosawa, K. Fukuda, D. Totsuka, K. Watanabe, A. Yamazaki, Y. Yokota, A. Yoshikawa, Cryst. Growth Des. 12 (2012) 142. [15] Y. Fujimoto, T. Yanagida, Y. Yokota, N. Kawaguchi, K. Fukuda, D. Totsuka, K. Watanabe, A. Yamazaki, V. Chani, A. Yoshikawa, Phys. Status Solidi B 248 (2010) 444. [16] W.H. Zachariasen, Proc. Natl. Acad. Sci. U. S. A. 17 (11) (1931) 617. [17] H.J. Seo, B.K. Moon, B.J. Kim, J.B. Kim, T. Tsuboi, J. Phys.: Condens. Matter 11 (1999) 7635. [18] J.B. Kim, K.S. Lee, I.H. Suh, J.H. Lee, J.R. Park, Y.H. Shin, Acta Crystallogr. C 52 (1996) 498. [19] T. Yanagida, H. Takahashi, T. Ito, D. Kasama, T. Enoto, M. Sato, S. Hirakuri, M. Kokubun, K. Makishima, T. Yanagitani, H. Yagi, T. Shigeta, T. Ito, IEEE Trans. Nucl. Sci. 52 (2005) 1836. [20] J. Ueda, K. Aishima, S. Tanabe, Opt. Mater. 35 (2013) 1952. [21] E.G. Yukihara, L.G. Jacobsohn, M.W. Blair, B.L. Bennett, S.C. Tornga, R.E. Muenchausen, J. Lumin. 130 (2010) 2309. [22] T. Yanagida, K. Kamada, Y. Fujimoto, H. Yagi, T. Yanagitani, Opt. Mater. 35 (2013) 2480. [23] Y. Fujimoto, T. Yanagida, Y. Yokota, N. Kawaguchi, K. Fukuda, D. Totsuka, K. Watanabe, A. Yamazaki, A. Yoshikawa, J. Cryst. Growth 318 (2010) 784. [24] P. Dorenbos, J. Lumin. 91 (2000) 155.
Contents lists available at ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Photoluminescence, photo-stimulated luminescence and thermoluminescence properties of CaB2O4 crystals activated with Ce3+ Yutaka Fujimoto a,⇑, Takayuki Yanagida b, Masanori Koshimizu a, Keisuke Asai a a b
Tohoku University, 6-6-04, Aramaki Aza Aoba Aoba-ku, Sendai, Miyagi 980-8579, Japan Kyushu Institute of Technology, 2-4, Hibikino, Wakamatsu-ku, Kitakyushu, Fukuoka 808-0196, Japan
a r t i c l e
i n f o
Article history: Available online 29 December 2014 Keywords: Photo-stimulated luminescence Thermoluminescence Ce3+ 5d–4f transition
a b s t r a c t Photoluminescence (PL), photo-stimulated luminescence (PSL), and thermoluminescence (TL) properties of a Ce-doped CaB2O4 crystal were studied. The Ce-doped crystal was prepared by the simple solidification method using a Pt crucible under nitrogen atmosphere. A PL emission band in the 350–370 nm wavelength range was obtained under excitation at 325 nm owing to the 5d (t2g)–4f (2F5/2, 2F7/2)-allowed transition of the Ce3+ emission center. The fluorescence quantum efficiency and the decay time of Ce3+ were estimated to be about 70% and 29 ns, respectively. The 5d–4f emission band of Ce3+ also appeared in the 350–370 nm wavelength range in the TL and PSL spectra. Good linear TL and PSL responses were observed in the 1–1000 mGy and 1–10,000 mGy X-ray dose range, respectively. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Photo-stimulated luminescence (PSL) and thermoluminescence (TL) exhibited by inorganic crystals and glasses irradiated with X-rays, gamma-rays, and neutrons are interesting phenomena, both from the fundamental as well as practical viewpoints. The ionizing radiation leaves the host material in a metastable state, which is characterized by the electrons and holes separately trapped at defects in the host matrix. During the PSL and TL processes, visible light and heat stimulates the release of the electrons and holes from these trapping centers, resulting in electron–hole recombination and the excitation of emission centers in the host material. Many studies have been conducted to better understand the detailed mechanism of PSL and TL and to apply these phenomena to materials for radiation dosimetry. After a great deal of effort, BaFBr:Eu [1,2], LiF:Mg, Cu, P [3,4] and Al2O3:C [5,6] are now available for use as imaging plates and personal dosimeters. Recently, the PSL and TL properties of borate based phosphors have been reported because of their good tissue equivalence and excellent sensitivity to X-rays, gamma-rays, and neutrons. Among the borate-based phosphors, the use of alkali-earth tetra-borate crystals (such as MgB4O7, CaB4O7, and SrB4O7) activated with rare-earth and transition-metal ions as the TL material has been investigated by several researchers [7–12]. Our group has studied the PSL and TL properties of other types of alkali-earth borate ⇑ Corresponding author. Tel.: +81 22 795 7219. E-mail address: [email protected] (Y. Fujimoto). http://dx.doi.org/10.1016/j.optmat.2014.11.049 0925-3467/Ó 2014 Elsevier B.V. All rights reserved.
crystals in recent years. The present study focuses on calcium meta-borate (CaB2O4) crystals. We selected this compound because its chemical composition is similar to that of CaB4O7, which has demonstrated intense emission owing to lattice defects and rare-earth ionic dopants [13–15]. To the best of our knowledge, no other observations on both PSL and TL from CaB2O4 crystal activated with Ce3+ have been reported so far. In this communication, the basic PL, PSL, and TL properties of Ce3+:CaB2O4 crystals are reported and discussed.
2. Experimental procedures The Ce3+:CaB2O4 crystal sample was grown by the simple solidification method. The starting materials were prepared from a stoichiometric mixture of CaCO3 (4N), H3BO3 (4N), and CeO2 (4N) powders. The Ce concentration was 0.5% (nominal composition) and the mixed powders were placed in a Pt crucible (50 mm in both diameter and height). The crucibles were set in the electric furnace and enclosed by the MoSi2 resist heater. The crucible was heated up to 1160 °C (the melting point of CaB2O4) and maintained at this temperature for about 10 h under a nitrogen atmosphere. The furnace was then cooled to room temperature at a cooling rate of 1 °C/min. The transmittance spectrum of the Ce-doped crystal was recorded in the 190–2700 nm wavelength regime with a JASCO V-670 spectrometer. The spectrometer was equipped with a photomultiplier tube (PMT) and a Peltier-cooled PbS detector for use in the UV–VIS and the NIR–IR regions, respectively. The light sources for both the regions were deuterium and halogen lamps.
50
Y. Fujimoto et al. / Optical Materials 41 (2015) 49–52
To determine the basic luminescence properties of Ce3+, we demonstrated the photoluminescence (PL) map using a Quantaurus-QY system (Hamamatsu). This system consists of a Xe-lamp, a monochromator, an integrating sphere, a multichannel detector, and a personal computer. The fluorescence quantum efficiency (QE) of Ce3+ at room temperature was calculated using the difference between the number of photons emitted from a sample and the number of photons absorbed by a sample using an integrating sphere. The TL glow curve of the Ce3+-doped crystal was measured in air with a TL-2000 reader manufactured by Nanogray Inc. A linear heating rate of 1 K s 1 was used to record the glow curves, and the TL intensities were recorded in the temperature range 320– 700 K. An original X-ray generator (XRB80P Monoblock, Spellman) equipped with a tungsten target was used as the irradiation source. The generator was supplied with a voltage of 40 kV and current in the range 0.5–5 mA. X-ray irradiation doses of 1, 10, 100, and 1000 mGy were chosen for the measurements. After the measurements, the sample was annealed at 800 K with each cycle as a reset process. The TL spectrum of the Ce3+-doped crystal was evaluated with a SR163i-UV spectrometer combined with a DU920P CCD detector (Andor). The TL photons emitted from the sample were sent to the spectrometer using an optical fiber to avoid direct heating. After irradiation of the sample with 1000 mGy, the spectra under thermo-stimulated condition were recorded at 360 K. The integration time for this experiment was 20 s. The PSL properties of the Ce3+-doped crystal were examined using a Quantaurus-Tau (Hamamatsu Photonics Co.) fluorophotometer. A light-emitting diode (LED) wavelength of 630 nm was used as the optimum stimulation light, and the X-ray irradiation doses were 1, 10, 100, 1000, and 10,000 mGy. The PSL spectra were recorded at room temperature.
Fig. 2. Optical transmittance spectrum of the Ce-doped crystal in the UV–NIR wavelength region.
3. Results and discussions The Ce3+-doped crystal obtained was clear and colorless, with cleavage cracks observed, as shown in Fig. 1. Previous studies have reported that the cracks arise owing to the (B2O4)n2n layers parallel to the c-axis in the CaB2O4 lattice [16–18]. Fig. 2 illustrates the transmittance spectrum of the Ce3+-doped crystal. In the spectrum, the absorption bands appeared in the 230–325 nm wavelength region owing to the allowed transition from the 4f ground state to the 5d excited states (t2g, e2g) of Ce3+. In the 350–2700 nm wavelength range, the crystal showed no absorption lines and exhibited high transmittance of more than 75%. In the PL map (Fig. 3), an intense emission band was observed in the 350–370 nm wavelength range, when light at 325 nm excited the crystal. The ultraviolet emission band is assigned to the transition from the Ce3+5d (t2g) state to the 4f ground-state levels
Fig. 1. View of the as grown Ce (0.5%)-doped CaB2O4 crystal.
Fig. 3. PL map of the Ce-doped crystal at room temperature.
(2F5/2 and 2F7/2). The fluorescence QE for the emission was approximately 70%. The emission wavelength in the case of Ce3+:CaB2O4 was short compared to commercial oxide phosphors activated with Ce3+ such as Ce3+:Y3Al5O12, Ce3+:Gd2SiO5, Ce3+:L2SiO5, and Ce3+:Gd3Al2Ga3O12 [19–23]. This can be considered to be a result of the influence of the host crystal lattice on the splitting of 5d levels of Ce3+, because the 5d levels are significantly affected by the ligand field of the first coordination sphere [24]. Fig. 4 shows the TL glow curve of the Ce3+-doped (a) and undoped (b) crystals irradiated with 1000 mGy X-rays. In the case of the Ce3+-doped crystal, an intense glow peak at 360 K was observed, while the TL glow curve for the undoped crystal showed three peaks at 425 K, 510 K, and 610 K. The glow peaks of the undoped crystal are associated with the intrinsic electron trap centers caused by various lattice defects in the host lattice. The glow peak at 360 K for the Ce3+-doped crystal may be due to other charged point defects such as oxygen vacancies or calcium vacancies because it is expected that Ce3+ ion occupy Ca2+ cationic site. Additionally another possible factor is the Ce3+ ion which acts as a hole trap center. The dose dependence of the glow peak intensities is illustrated in Fig. 5. According to the result, the Ce3+-doped crystal was found to exhibit a good linear response in the 1–1000 mGy irradiation dose range. The TL spectra are shown in
Y. Fujimoto et al. / Optical Materials 41 (2015) 49–52
51
Fig. 4. TL glow curves of the Ce-doped crystal (a) compared with the undoped crystal (b).
Fig. 7. PSL spectrum of the Ce-doped crystal under stimulation with 630 nm LED light.
Fig. 5. Dose response of the TL glow peak intensities in the Ce-doped crystal.
Fig. 8. Dose response of the PSL peak intensities of the Ce-doped crystal.
and they recombine through the Ce3+ emission centers by heating stimulation. The PSL spectrum of the Ce3+-doped crystal irradiated with 1000 mGy X-rays is presented in Fig. 7. In the spectrum, an emission band corresponding to Ce3+ was observed in the 350– 370 nm wavelength range, which is consistent with the PL and TL spectra. Thus, it can be concluded that the electrons and holes in the trap centers can be released by visible light stimulation. With our experimental system, a linear PSL response in the dose range 1–10,000 mGy was observed, as shown in Fig. 8. 4. Summary
Fig. 6. TL spectrum of the Ce-doped crystal stimulated by heating to 360 K.
Fig. 6. The spectrum showed an intense emission band in the 350– 370 nm wavelength range, just as in the case of the PL spectrum. It is clear that part of the electrons and holes generated by irradiating the sample with X-rays is trapped in the shallow trap centers in the host crystal. When they are subsequently released from the traps,
The basic PL, PSL, and TL properties of Ce3+-doped CaB2O4 crystal were studied. The PL spectrum obtained by excitation at 325 nm showed an intense emission band in the 350–370 nm wavelength range owing to the transition from the Ce3+5d (t2g) state to the 4f ground-state levels (2F5/2 and 2F7/2). The PL quantum efficiency of Ce3+ was estimated to be about 70%. The TL and PSL spectra also exhibited the Ce3+ 5d–4f emission band in the 350– 370 nm wavelength range when stimulated by heating to 360 K and by exposing to 630 nm-light, respectively. From the result, it follows that the electrons and holes trapped in the shallow traps owing to irradiation by X-rays were released by heating and light stimulation; they subsequently and then they recombined with the holes through the Ce3+ emission centers. The measurement of
52
Y. Fujimoto et al. / Optical Materials 41 (2015) 49–52
the dose response showed good linear TL and PSL responses in the 1–1000 mGy and 1–10,000 mGy ranges, respectively. References [1] K. Takahashi, K. Kohda, J. Miyhara, Y. Kanemitsu, K. Amitani, S. Shionoya, J. Lumin. 31 and 32 (1984) 266. [2] Y. Amemiya, J. Miyhara, Nature 336 (1988) 89. [3] W. Shoushan, C. Goulong, W. Fang, L. Yuanfang, Z. Ziying, Z. Jianhuan, Radiat. Prot. Dosim. 14 (3) (1986) 223. [4] C.M.H. Driscoll, A.F. McWhan, J.B. O’Hagan, J. Dodson, S.J. Mundy, C.D. Todd, Radiat. Prot. Dosim. 17 (1986) 367. [5] B.G. Markey, L.E. Colyott, S.W.S. Mckeever, Radiat. Meas. 24 (1995) 457. [6] S.W.S. McKeever, M.S. Akselrod, B.G. Markey, Radiat. Prot. Dosim. 65 (1996) 267. [7] M. Prokic, Nucl. Instrum. Methods 175 (1980) 83. [8] C. Furetta, M. Prokic, R. Salamon, G. Kitis, Appl. Radiat. Isot. 52 (2) (2000) 243. [9] E. Tekin, A. Ege, T. Karali, P.D. Townsend, M. Proki, Radiat. Meas. 45 (2010) 764. [10] M.E. Haghiri, E. Saion, N. Soltani, W. Wan Abdullah, M. Navasery, M. Hashim, J. Lumin. 141 (2013) 177. [11] M. Santiago, C. Grasseli, E. Caselli, M. Lester, A. Lavat, F. Spano, Phys. Status Solidi A 185 (2001) 285. [12] R.P. Yavetskiy, E.F. Dolzhenkova, A.V. Tolmachev, S.V. Parkhomenko, V.N. Baumer, A.L. Prosvirnin, J. Alloys Compd. 441 (2007) 202.
[13] I.V. Berezovskaya, N.P. Efryushina, A.S. Voloshinovskii, G.B. Stryganyuk, P.V. Pir, V.P. Dotsenko, Radiat. Meas. 42 (2007) 878. [14] Y. Fujimoto, T. Yanagida, N. Kawaguchi, S. Kurosawa, K. Fukuda, D. Totsuka, K. Watanabe, A. Yamazaki, Y. Yokota, A. Yoshikawa, Cryst. Growth Des. 12 (2012) 142. [15] Y. Fujimoto, T. Yanagida, Y. Yokota, N. Kawaguchi, K. Fukuda, D. Totsuka, K. Watanabe, A. Yamazaki, V. Chani, A. Yoshikawa, Phys. Status Solidi B 248 (2010) 444. [16] W.H. Zachariasen, Proc. Natl. Acad. Sci. U. S. A. 17 (11) (1931) 617. [17] H.J. Seo, B.K. Moon, B.J. Kim, J.B. Kim, T. Tsuboi, J. Phys.: Condens. Matter 11 (1999) 7635. [18] J.B. Kim, K.S. Lee, I.H. Suh, J.H. Lee, J.R. Park, Y.H. Shin, Acta Crystallogr. C 52 (1996) 498. [19] T. Yanagida, H. Takahashi, T. Ito, D. Kasama, T. Enoto, M. Sato, S. Hirakuri, M. Kokubun, K. Makishima, T. Yanagitani, H. Yagi, T. Shigeta, T. Ito, IEEE Trans. Nucl. Sci. 52 (2005) 1836. [20] J. Ueda, K. Aishima, S. Tanabe, Opt. Mater. 35 (2013) 1952. [21] E.G. Yukihara, L.G. Jacobsohn, M.W. Blair, B.L. Bennett, S.C. Tornga, R.E. Muenchausen, J. Lumin. 130 (2010) 2309. [22] T. Yanagida, K. Kamada, Y. Fujimoto, H. Yagi, T. Yanagitani, Opt. Mater. 35 (2013) 2480. [23] Y. Fujimoto, T. Yanagida, Y. Yokota, N. Kawaguchi, K. Fukuda, D. Totsuka, K. Watanabe, A. Yamazaki, A. Yoshikawa, J. Cryst. Growth 318 (2010) 784. [24] P. Dorenbos, J. Lumin. 91 (2000) 155.