- Email: [email protected]
Growth and luminescent properties of the Ce, Pr doped NaCl single crystals grown by the modified micro-pulling-down method
Radiation Measurements 45 (2010) 472–474
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Growth and luminescent properties of the Ce, Pr doped NaCl single crystals grown by the modified micro-pulling-down method Yuui Yokota a, *, Takayuki Yanagida a, Yutaka Fujimoto a, Martin Nikl b, Akira Yoshikawa a, c a
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University/2-1-1, Katahira, Aoba-ku, Sendai, Japan Institute of Physics, the Academy of Sciences of the Czech Republic/6253, Prague, Czech Republic c New Industry Creation Hatchery Center (NICHe), Tohoku University/2-1-1, Katahira, Aoba-ku, Sendai, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 August 2009 Received in revised form 25 September 2009 Accepted 18 November 2009
We have investigated luminescent properties of nondope, Ce and Pr doped NaCl [nondope NaCl, Ce:NaCl, Pr:NaCl] single crystals grown by a modified micro-pulling-down method with a removable chamber system. Nondope, Ce 1% and Pr 1% doped NaCl crystals with a single phase of NaCl structure were obtained and the crystals indicated general crystal quality by the X-ray rocking curve measurement. For the nondope NaCl and Pr:NaCl crystals, the transmittance spectra indicated almost more than 60% in the wavelength from 200 to 800 nm and an absorption of Ce3þ ion was observed in the transmittance spectrum of Ce:NaCl crystal. The emission spectrum originated from Ce3þ 5d–4f transition appeared around 300 nm in the photoluminescence spectrum and the decay time was 19.7 ns. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Crystal growth Luminescence Scintillator
1. Introduction Scintillator materials which emit photons by an exposure of radiation have been investigated energetically in the world and were used as a radiation detector in collaboration with a photo acceptance unit such as a photo multiplier tube and photo diode. Chloride, boride and iodide scintillators as represented by Ce:LaBr3 (van Loef et al., 2001), Ce:LaCl3 (van Loef et al., 2000) and Ce:LuI3 (Glodo et al., 2005) have several great features such as high light yield and high energy resolution due to the small band gap (Dorenbos, 2002). However, these halide materials have a high hygroscopic nature and it’s difficult to make their single crystals without effects of moisture. Micro-pulling-down (m-PD) method with an advantage of high crystal growth speed (0.01–0.1 mm/min, one crystal bar a day) have been used for many single crystal growths of oxide and fluoride scintillators such as Pr:Lu3Al5O12 (Ogino et al., 2006) and Ce:PrF3 (Yoshikawa et al., 2004) and so on. In contrast, halide crystals except fluoride haven’t been grown by m-PD method so far due to the high hygroscopic nature. On these backgrounds, we newly developed a modified m-PD method with a removable chamber system (Fig. 1) and the first crystal growth of chloride crystals, nondope NaCl, Ce doped NaCl
* Corresponding author. E-mail address: [email protected] (Y. Yokota). 1350-4487/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2009.11.036
[Ce:NaCl] and Pr doped NaCl [Pr:NaCl] by the m-PD method were performed. 2. Experimental Nondoped, Ce 1% and Pr 1% doped NaCl single crystals with nominal compositions, (Na1xREx)Cl12x (x ¼ 0, 0.001, RE ¼ Ce, Pr) were grown by the modified m-PD method with a removable chamber (Fig. 1). In a globe box with less than 1 ppm concentration of oxygen and moisture, starting materials, NaCl, CeCl3 and PrCl3 (>3N purity), were mixed in a mortar and entered into a carbon crucible. The crucible was placed in the center of removable chamber and the chamber was taken out from the globe box. The chamber was connected m-PD apparatus and high-purity Ar gas (>99.9999%) was entered in the chamber after vacuuming up to w104 Pa. Pulling down of the crystal was performed with 0.1 mm/ min growth speed using a Pt wire as a seed. After crystal growth was finished, the chamber was entered into the globe box again and grown crystal was taken out from the chamber. The phases of grown crystals were identified by powder X-ray diffraction measurement (RIGAKU Rint2000) and these lattice parameters were calculated from the XRD patterns using Ti powder as an internal standard. The crystal qualities were measured by X-ray rocking curve (XRC) analysis using in-plane X-ray diffractometer (RIGAKU ATX-G). u scan was investigated for the reflection of (2 0 0) from the crystals. Transmittance, emission spectra and decay time of the crystals were measured
Y. Yokota et al. / Radiation Measurements 45 (2010) 472–474
Fig. 1. Schematic of a modified m-PD method with a removable chamber.
by spectrophotometer (JASCO V530) and spectrofluorometer (EDINBURGH INSTRUMENTS FLS920). 3. Results and discussion Nondope NaCl and Ce 1% and Pr 1% doepd NaCl single crystals with 30–50 mm length were grown by modified m-PD method as
473
shown in Fig. 2a. Nondope NaCl crystal indicated transparent in all parts. In contrast, Ce and Pr doped NaCl crystals had little white clouded parts on the surface. Powder X-ray patterns of these crystals were shown in Fig. 2d. All crystals indicated a single phase of NaCl with cubic structure. Lattice parameters of Ce:NaCl and Pr:NaCl crystals which were calculated from these XRD patterns were smaller than that of nondope NaCl crystal. This result suggests that Ce3þ and Pr3þ doping to Naþ site generates Cl defects and the anion defects induce lattice shrinkage of the crystals. XRC u scans carried out for the reflection from (2 0 0) plane corresponding to the [1 0 0] on nondope NaCl single crystal in order to investigate the crystal quality (Fig. 3a). The XRC peak from (2 0 0) plane of nondope NaCl single crystal indicated a single peak with 49.3 arcsec full-width at half-maximum (FWHM), which was general value of m-PD crystals. In contrast, the shape of curve was asymmetry with a shoulder originated from mosaicity or phase separation. Fig. 3b shows transmittance of nondope NaCl, Ce:NaCl and Pr:NaCl crystals. Nondope and Pr:NaCl crystals indicated almost more than 60% transmittance in the wavelength from 200 to 800 nm. However, transmittance of Ce:NaCl crystal was less than 60% and a large decrease of transmittance was observed especially below 300 nm compared to other crystals. This result suggests that Ce:NaCl crystal has the absorption from Cl defects and a similar effect was reported for Ca2þ doped YAlO3 crystal with oxygen
Fig. 2. (a) Nondope (b) Ce 1% and (c) Pr 1% doped NaCl crystals grown by the modified m-PD method. (d) Powder XRD patterns and lattice parameters of grown crystals.
Fig. 3. (a) X-ray rocking curve of nondope NaCl crystal and (b) transmittance of nondope NaCl, Ce:NaCl and Pr:NaCl crystals.
474
Y. Yokota et al. / Radiation Measurements 45 (2010) 472–474
Fig. 4. (a) Photoluminescence spectra nondope NaCl, Ce:NaCl and Pr:NaCl crystals and (b) decay time of Ce:NaCl crystals.
defects (Kawabe et al., 2006). In addition, the absorption which was considered to originate from the Ce3þ ion was observed around 300 nm in the Ce:NaCl crystal. Meanwhile, the clear absorption of Pr3þ ion didn’t appear in the transition spectrum, suggesting that the concentration of Pr3þ ion in Pr:NaCl crystal was very small. In the photoluminescence spectra of nondope NaCl, Ce:NaCl and Pr:NaCl crystals (Fig. 4a), Ce:NaCl crystal indicated a emission peak around 375 nm originated form Ce3þ 5d–4f transition by 290 nm excitation. Meanwhile, emission peak from Pr3þ couldn’t be observed for Pr:NaCl crystal because the energy of quanta with 290 nm is insufficient to excite the dipole allowed d–f luminescence. Decay time of the emission from Ce3þ ion in Ce:NaCl crystal was shown in Fig. 4b. Exponential fitting to the decay curve indicated that the decay time was 19.7 ns.
4. Conclusions We grew nondope, Ce 1% and Pr 1% doped NaCl single crystals by the modified m-PD method with a removable chamber. Nondope and Pr doped NaCl crystals indicated almost more than 60% transmittance and the absorption of Ce3þ ion was observed for Ce doped NaCl crystal. In Photoluminescence measurement, emission peak of Ce3þ 5d–4f with the 19.7 ns daytime appeared around 375 nm. This investigation is the first crystal growth of chloride by
m-PD method and a first step of material search on halide scintillator crystals by m-PD method. Acknowledgment This work was partially supported by Ministry of Ministry of Health and Welfare, Grant-in-Aid for the development of medical instruments and Ministry of Education. This work was also partially supported by Ministry of Education, Culture, Sports, Science and Technology of Japanese government, Grant-in-Aid for Young Scientists (A), 19686001 (AY). Partial support of joint project between JSPS and ASCR, and Czech GAAV project M100100910 is also appreciated. References Dorenbos, P., 2002. Nucl. Instrm. Meth. Phys. Res. A486, 208. Glodo, J., Shah, K.S., Klugerman, M., Wong, P., Higgins, W., Dorenbos, P., 2005. Nucl. Instrm. Meth. Phys. Res. A537, 279. Kawabe, Y., Yamanaka, A., Horiuchi, H., Takashima, H., Hanamura, E., 2006. J. Lumin. 121, 517. van Loef, E.V.D., Dorenbos, P., van Eijik, C.W.E., Kramer, K.W., Gudel, H.U., 2000. Appl. Phys. Lett. 77, 1467. van Loef, E.V.D., Dorenbos, P., van Eijik, C.W.E., Kramer, K.W., Gudel, H.U., 2001. Appl. Phys. Lett. 79, 1573. Ogino, H., Yoshikawa, A., Nikl, M., Krasnikov, A., Kamada, K., Fukuda, T., 2006. J. Crys. Growth 287, 335. Yoshikawa, A., Satonaga, T., Kamada, K., Sato, H., Nikl, M., Solovieva, N., Fukuda, T., 2004. J. Cryst. Growth 270, 427.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Growth and luminescent properties of the Ce, Pr doped NaCl single crystals grown by the modified micro-pulling-down method Yuui Yokota a, *, Takayuki Yanagida a, Yutaka Fujimoto a, Martin Nikl b, Akira Yoshikawa a, c a
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University/2-1-1, Katahira, Aoba-ku, Sendai, Japan Institute of Physics, the Academy of Sciences of the Czech Republic/6253, Prague, Czech Republic c New Industry Creation Hatchery Center (NICHe), Tohoku University/2-1-1, Katahira, Aoba-ku, Sendai, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 August 2009 Received in revised form 25 September 2009 Accepted 18 November 2009
We have investigated luminescent properties of nondope, Ce and Pr doped NaCl [nondope NaCl, Ce:NaCl, Pr:NaCl] single crystals grown by a modified micro-pulling-down method with a removable chamber system. Nondope, Ce 1% and Pr 1% doped NaCl crystals with a single phase of NaCl structure were obtained and the crystals indicated general crystal quality by the X-ray rocking curve measurement. For the nondope NaCl and Pr:NaCl crystals, the transmittance spectra indicated almost more than 60% in the wavelength from 200 to 800 nm and an absorption of Ce3þ ion was observed in the transmittance spectrum of Ce:NaCl crystal. The emission spectrum originated from Ce3þ 5d–4f transition appeared around 300 nm in the photoluminescence spectrum and the decay time was 19.7 ns. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Crystal growth Luminescence Scintillator
1. Introduction Scintillator materials which emit photons by an exposure of radiation have been investigated energetically in the world and were used as a radiation detector in collaboration with a photo acceptance unit such as a photo multiplier tube and photo diode. Chloride, boride and iodide scintillators as represented by Ce:LaBr3 (van Loef et al., 2001), Ce:LaCl3 (van Loef et al., 2000) and Ce:LuI3 (Glodo et al., 2005) have several great features such as high light yield and high energy resolution due to the small band gap (Dorenbos, 2002). However, these halide materials have a high hygroscopic nature and it’s difficult to make their single crystals without effects of moisture. Micro-pulling-down (m-PD) method with an advantage of high crystal growth speed (0.01–0.1 mm/min, one crystal bar a day) have been used for many single crystal growths of oxide and fluoride scintillators such as Pr:Lu3Al5O12 (Ogino et al., 2006) and Ce:PrF3 (Yoshikawa et al., 2004) and so on. In contrast, halide crystals except fluoride haven’t been grown by m-PD method so far due to the high hygroscopic nature. On these backgrounds, we newly developed a modified m-PD method with a removable chamber system (Fig. 1) and the first crystal growth of chloride crystals, nondope NaCl, Ce doped NaCl
* Corresponding author. E-mail address: [email protected] (Y. Yokota). 1350-4487/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2009.11.036
[Ce:NaCl] and Pr doped NaCl [Pr:NaCl] by the m-PD method were performed. 2. Experimental Nondoped, Ce 1% and Pr 1% doped NaCl single crystals with nominal compositions, (Na1xREx)Cl12x (x ¼ 0, 0.001, RE ¼ Ce, Pr) were grown by the modified m-PD method with a removable chamber (Fig. 1). In a globe box with less than 1 ppm concentration of oxygen and moisture, starting materials, NaCl, CeCl3 and PrCl3 (>3N purity), were mixed in a mortar and entered into a carbon crucible. The crucible was placed in the center of removable chamber and the chamber was taken out from the globe box. The chamber was connected m-PD apparatus and high-purity Ar gas (>99.9999%) was entered in the chamber after vacuuming up to w104 Pa. Pulling down of the crystal was performed with 0.1 mm/ min growth speed using a Pt wire as a seed. After crystal growth was finished, the chamber was entered into the globe box again and grown crystal was taken out from the chamber. The phases of grown crystals were identified by powder X-ray diffraction measurement (RIGAKU Rint2000) and these lattice parameters were calculated from the XRD patterns using Ti powder as an internal standard. The crystal qualities were measured by X-ray rocking curve (XRC) analysis using in-plane X-ray diffractometer (RIGAKU ATX-G). u scan was investigated for the reflection of (2 0 0) from the crystals. Transmittance, emission spectra and decay time of the crystals were measured
Y. Yokota et al. / Radiation Measurements 45 (2010) 472–474
Fig. 1. Schematic of a modified m-PD method with a removable chamber.
by spectrophotometer (JASCO V530) and spectrofluorometer (EDINBURGH INSTRUMENTS FLS920). 3. Results and discussion Nondope NaCl and Ce 1% and Pr 1% doepd NaCl single crystals with 30–50 mm length were grown by modified m-PD method as
473
shown in Fig. 2a. Nondope NaCl crystal indicated transparent in all parts. In contrast, Ce and Pr doped NaCl crystals had little white clouded parts on the surface. Powder X-ray patterns of these crystals were shown in Fig. 2d. All crystals indicated a single phase of NaCl with cubic structure. Lattice parameters of Ce:NaCl and Pr:NaCl crystals which were calculated from these XRD patterns were smaller than that of nondope NaCl crystal. This result suggests that Ce3þ and Pr3þ doping to Naþ site generates Cl defects and the anion defects induce lattice shrinkage of the crystals. XRC u scans carried out for the reflection from (2 0 0) plane corresponding to the [1 0 0] on nondope NaCl single crystal in order to investigate the crystal quality (Fig. 3a). The XRC peak from (2 0 0) plane of nondope NaCl single crystal indicated a single peak with 49.3 arcsec full-width at half-maximum (FWHM), which was general value of m-PD crystals. In contrast, the shape of curve was asymmetry with a shoulder originated from mosaicity or phase separation. Fig. 3b shows transmittance of nondope NaCl, Ce:NaCl and Pr:NaCl crystals. Nondope and Pr:NaCl crystals indicated almost more than 60% transmittance in the wavelength from 200 to 800 nm. However, transmittance of Ce:NaCl crystal was less than 60% and a large decrease of transmittance was observed especially below 300 nm compared to other crystals. This result suggests that Ce:NaCl crystal has the absorption from Cl defects and a similar effect was reported for Ca2þ doped YAlO3 crystal with oxygen
Fig. 2. (a) Nondope (b) Ce 1% and (c) Pr 1% doped NaCl crystals grown by the modified m-PD method. (d) Powder XRD patterns and lattice parameters of grown crystals.
Fig. 3. (a) X-ray rocking curve of nondope NaCl crystal and (b) transmittance of nondope NaCl, Ce:NaCl and Pr:NaCl crystals.
474
Y. Yokota et al. / Radiation Measurements 45 (2010) 472–474
Fig. 4. (a) Photoluminescence spectra nondope NaCl, Ce:NaCl and Pr:NaCl crystals and (b) decay time of Ce:NaCl crystals.
defects (Kawabe et al., 2006). In addition, the absorption which was considered to originate from the Ce3þ ion was observed around 300 nm in the Ce:NaCl crystal. Meanwhile, the clear absorption of Pr3þ ion didn’t appear in the transition spectrum, suggesting that the concentration of Pr3þ ion in Pr:NaCl crystal was very small. In the photoluminescence spectra of nondope NaCl, Ce:NaCl and Pr:NaCl crystals (Fig. 4a), Ce:NaCl crystal indicated a emission peak around 375 nm originated form Ce3þ 5d–4f transition by 290 nm excitation. Meanwhile, emission peak from Pr3þ couldn’t be observed for Pr:NaCl crystal because the energy of quanta with 290 nm is insufficient to excite the dipole allowed d–f luminescence. Decay time of the emission from Ce3þ ion in Ce:NaCl crystal was shown in Fig. 4b. Exponential fitting to the decay curve indicated that the decay time was 19.7 ns.
4. Conclusions We grew nondope, Ce 1% and Pr 1% doped NaCl single crystals by the modified m-PD method with a removable chamber. Nondope and Pr doped NaCl crystals indicated almost more than 60% transmittance and the absorption of Ce3þ ion was observed for Ce doped NaCl crystal. In Photoluminescence measurement, emission peak of Ce3þ 5d–4f with the 19.7 ns daytime appeared around 375 nm. This investigation is the first crystal growth of chloride by
m-PD method and a first step of material search on halide scintillator crystals by m-PD method. Acknowledgment This work was partially supported by Ministry of Ministry of Health and Welfare, Grant-in-Aid for the development of medical instruments and Ministry of Education. This work was also partially supported by Ministry of Education, Culture, Sports, Science and Technology of Japanese government, Grant-in-Aid for Young Scientists (A), 19686001 (AY). Partial support of joint project between JSPS and ASCR, and Czech GAAV project M100100910 is also appreciated. References Dorenbos, P., 2002. Nucl. Instrm. Meth. Phys. Res. A486, 208. Glodo, J., Shah, K.S., Klugerman, M., Wong, P., Higgins, W., Dorenbos, P., 2005. Nucl. Instrm. Meth. Phys. Res. A537, 279. Kawabe, Y., Yamanaka, A., Horiuchi, H., Takashima, H., Hanamura, E., 2006. J. Lumin. 121, 517. van Loef, E.V.D., Dorenbos, P., van Eijik, C.W.E., Kramer, K.W., Gudel, H.U., 2000. Appl. Phys. Lett. 77, 1467. van Loef, E.V.D., Dorenbos, P., van Eijik, C.W.E., Kramer, K.W., Gudel, H.U., 2001. Appl. Phys. Lett. 79, 1573. Ogino, H., Yoshikawa, A., Nikl, M., Krasnikov, A., Kamada, K., Fukuda, T., 2006. J. Crys. Growth 287, 335. Yoshikawa, A., Satonaga, T., Kamada, K., Sato, H., Nikl, M., Solovieva, N., Fukuda, T., 2004. J. Cryst. Growth 270, 427.