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Effect of flux on the properties of CaAl2O4:Eu2+, Nd3+ long afterglow phosphor
Journal of Alloys and Compounds 458 (2008) 446–449
Effect of flux on the properties of CaAl2O4:Eu2+, Nd3+ long afterglow phosphor Xiaoming Teng, Weidong Zhuang ∗ , Yunsheng Hu, Chunlei Zhao, Huaqiang He, Xiaowei Huang National Engineering Research Center for Rare Earth Materials, General Research Institute for Nonferrous Metals, and Grirem Advanced Materials Co. Ltd., Beijing 100088, China Received 12 October 2006; received in revised form 27 March 2007; accepted 1 April 2007 Available online 6 April 2007
Abstract The long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ was prepared by high temperature solid-state reaction method under reducing atmosphere. The effect of flux H3 BO3 on the crystal structure and luminescent properties of the phosphor was studied. Results of XRD indicate that the volume of unit cell becomes smaller, and then the crystal field is changed, which results in the easier transition of 4f-5d. On the other hand, H3 BO3 addition is in favor of the formation of pure phase CaAl2 O4 . Both behaviors enhance the emission intensity of the obtained phosphor to some extent. But its emission peak does not shift evidently because the energy level difference of 4f-5d does not be changed obviously. Moreover, H3 BO3 also affects the afterglow properties of this phosphor. The optimized content of H3 BO3 is 0.06 mol/mol for the obtained phosphor with excellent properties. © 2007 Elsevier B.V. All rights reserved. Keywords: Rare earth; Long afterglow; Aluminate; Flux
1. Introduction
2. Experimental
The aluminate long afterglow phosphor has characteristics of high luminescent brightness, long afterglow time, good chemical stability, no pollutions, etc. So the aluminate long afterglow phosphor is widely applied in luminescent paint, night illumination, instrumental display, etc. [1–4]. The studies of aluminate system mainly have focused on doping with the second activator except Eu since 1990s, such as Dy, Nd, etc. It is hoped that the phosphor can form the proper trap energy level via doping microelement, thereby achieve the aim that enhance luminescent brightness and prolong afterglow time [5–7]. At the same time, the effect of flux on synthetic techniques and luminescent properties has become one of the hotspot in the aluminate luminescent materials activated by rare earth [8–11]. Chen et al. [12] studied the effect of B2 O3 on the properties of SrAl2 O4 :Eu2+ , Dy3+ prepared by sol–gel method. However, the action and mechanism of H3 BO3 in the phosphor are not clear completely. In this paper, the effect of flux H3 BO3 on structure and property of long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ has been studied by XRD, SEM, spectra and long afterglow properties.
The long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ was prepared by the high temperature solid-state reaction method. CaCO3 (3N), Al2 O3 (4N), Eu2 O3 (4N), Nd2 O3 (4N) were used as raw materials. Small quantities of H3 BO3 were introduced as flux. The mixture of raw materials was ground and then sintered at 1350 ◦ C for about 3 h under reducing atmosphere. The sample was cooled, grinded and sieved, and then the aluminate long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ was obtained. The afterglow brightness and time of the phosphor were measured by a ST-900PM photometer. Its excitation and emission spectra were detected by FluoroMax-II spectrofluorometer made in the United States. The crystal structure of the phosphor was checked using a MXP21VAHF-M21X X-ray diffractometer that was manufactured in Japan. The SEM analysis was conducted on JSM-6400 Scanning Electron Microscope made in Japan. Horiba LA-300 laser scattering particle size analyzer was used to characterize the particle size of this phosphor.
∗
Corresponding author. Tel.: +86 10 89583430 15; fax: +86 10 89583430 20. E-mail address: [email protected] (W. Zhuang).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.013
3. Results and discussion 3.1. X-ray diffraction analysis Fig. 1 shows XRD patterns of CaAl2 O4 :Eu2+ , Nd3+ long afterglow phosphor prepared with H3 BO3 as flux (a) and without H3 BO3 (b). By analyzing these diffractive peaks, it is easy to find that the CaAl2 O4 phase was produced fully. However, there are still some CaAl4 O7 impurity phases. The CaAl4 O7 will contam-
X. Teng et al. / Journal of Alloys and Compounds 458 (2008) 446–449
447
Fig. 1. The XRD patterns of CaAl2 O4 :Eu2+ , Nd3+ prepared with H3 BO3 as flux (a) and without H3 BO3 (b). (“o” belong to CaAl4 O7 impure phase, other diffraction peaks belong to CaAl2 O4 phase).
inate the luminescence of this phosphor. The addition of H3 BO3 has decreased the impure phase of CaAl4 O7 in this phosphor, which enhances the initial brightness and prolongs afterglow time of this phosphor to some extent. When the phosphor is doped with H3 BO3 as flux, parts of B entering crystal lattice replace Al. However, large parts of B do not enter crystal lattice, which melt at low temperature and act as flux for the synthesis of the phosphor. It is suitable for producing pure phase and easy to hold integrality of crystal due to the low melting point of the compound. B which do not enter crystal lattice are help to urge activator ions entering crystal lattice and form luminescent center and trap center, which is easier to obtain single phase of CaAl2 O4 . 3.2. SEM analysis
Fig. 2. SEM photos of the phosphor synthesized with H3 BO3 as flux (a) and without H3 BO3 (b).
Fig. 2 is the SEM photos of the phosphor synthesized with H3 BO3 as flux (a) and without H3 BO3 (b). Table 1 lists the particle size of the phosphor. Obviously, the particle size of phosphor synthesized without H3 BO3 is smaller. While H3 BO3 was added to reaction system as flux, H3 BO3 participates in the solidstate reaction and quickens the rate of reaction. Liquid interfaces are produced among crystal grains, and then the crystal grains reunite and result in the bigger particle size. 3.3. Spectra analysis Fig. 3 is the emission spectra of the phosphor synthesized with H3 BO3 as flux and without H3 BO3 (λex = 365 nm). The emission spectra show a broadband emission peak from Eu2+ , which is Table 1 Particle size of the phosphor synthesized with H3 BO3 as flux and without H3 BO3 Sample
D10 (m)
D50 (m)
D90 (m)
No flux H3 BO3
3.07 6.22
19.71 30.74
79.55 97.43
Fig. 3. Emission spectra of CaAl2 O4 :Eu2+ , Nd3+ synthesized with H3 BO3 as flux (a) and without H3 BO3 (b).
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X. Teng et al. / Journal of Alloys and Compounds 458 (2008) 446–449
Table 2 Cell parameters of the phosphor synthesized with H3 BO3 as flux and without H3 BO3 Sample
a (nm)
b (nm)
c (nm)
V (nm3 )
No flux H3 BO3
0.8697 0.8691
0.8090 0.8082
1.5211 1.5208
1.0702 1.0682
due to the transition of Eu2+ that originates from 4f6 5d excitation state to 4f7 ground state. As shown in Fig. 3, the position of the emission peak does not change when the phosphor is doped with H3 BO3 as flux, which is centered at about 440 nm. But the emission intensity of the phosphor prepared with H3 BO3 is much higher than that of the phosphor prepared without H3 BO3 . Generally, the luminescence of CaAl2 O4 :Eu2+ , Nd3+ originates from the 4f-5d electron transition of Eu2+ . When the crystal field is changed, the energy difference between 4f-5d electron will change accordingly, which will lead to the shift of emission peak [11]. However, the emission spectra in Fig. 3 show the position of emission peak does not change evidently when the phosphor was synthesized with H3 BO3 as flux. It is explained that the crystal field surroundings of Eu2+ are not changed too much after B is introduced in the lattice. On the other hand, the crystal cell volume of CaAl2 O4 is 1.0691 nm3 (shown in Table 2). It has the trend to become small compared with that of synthesized without H3 BO3 . Its crystal cell volume is 1.0702 nm3 . When part of Al is replaced by B, the crystal is distorted because the radius of B is smaller than that of Al. The distortion may result in the easier 4f-5d transition of Eu2+ , and then the intensity of luminescence becomes stronger. At the same time, the reaction temperature is reduced due to H3 BO3 addition, which makes the reaction process completely and promotes the formation of pure phase CaAl2 O4 . Both behaviors enhance the emission intensity of the phosphor. 3.4. Effect of the content of H3 BO3 Figs. 4 and 5 show the effect of different content of H3 BO3 on long afterglow properties of CaAl2 O4 :Eu2+ , Nd3+ . Obviously, when the content of H3 BO3 is 0.06 mol/mol, the initial brightness of the phosphor is the best and the afterglow time is the longest. However, the luminescent properties of the phosphor become bad when the content of H3 BO3 continues to increase. 3.5. Mechanism of long afterglow luminescence and action of H3 BO3 In general, the long afterglow aluminate phosphor excited by Eu2+ can produce some trap energy levels with different depth due to doping with other rare earth ions, and thus prolong afterglow time [13,14]. Under 365 nm UV-excitation, the luminescence process of Eu2+ includes two parts: one is that the electrons at the excited state return ground state, and the other is that the electrons in trap energy level release to excitation state and then return ground state due to the thermal disturbance. The first part of luminescence does not exist after the excitation is stopped. The electrons
Fig. 4. Effect of the content of H3 BO3 on the initial brightness of CaAl2 O4 :Eu2+ , Nd3+ .
Fig. 5. The decay curve of CaAl2 O4 :Eu2+ , Nd3+ synthesized with different content of H3 BO3 (a, x = 0; b, x = 0.03; c, x = 0.06; d, x = 0.09 mol/mol).
captured and storaged at the trap energy level will be excited to 4f6 5d excitation state with the help of thermal disturbance, and then the electrons return 8 S7/2 ground state in succession, which leads to the characteristic luminescence of Eu2+ (shown in Fig. 6). The number of electrons storaged in the trap energy level is high density, and its depth is proper to releasing electrons at room temperature. So the phosphor possesses high afterglow brightness and long afterglow time [14,15].
Fig. 6. Mechanism of long afterglow luminescence in CaAl2 O4 :Eu2+ , Nd3+ .
X. Teng et al. / Journal of Alloys and Compounds 458 (2008) 446–449
However, the action of H3 BO3 is different from the abovementioned reason. When Eu2+ and Nd3+ replace Ca2+ , the crystal lattice produces distortion and the phosphor has higher energy barrier. When the phosphor is doped with H3 BO3 , B2 O3 has higher reaction activation energy, which can effectively reduce the energy barrier and make more Eu2+ and Nd3+ enter crystal lattice. Thus, the luminescent center ions and the density of traps become large. The afterglow properties of aluminate phosphor doped with rare earth ions have great connection with the lattice defect. The deeper the trap depth and the larger the density are, the better the afterglow properties are. Furthermore, when the phosphor is doped with H3 BO3 , the electron traps become deeper because the electronegativity of B is larger than Al and the radius of B is smaller than Al. So the afterglow properties of the CaAl2 O4 :Eu2+ , Nd3+ phosphor become better. 4. Conclusion The CaAl2 O4 :Eu2+ , Nd3+ phosphor was successfully synthesized by conventional solid-state reaction method. The addition of H3 BO3 as flux is in favor of formation of CaAl2 O4 pure phase, which enhances the intensity of emission of the phosphor. The position of the emission peak does not change evidently because the energy level difference of 4f-5d does not be changed obviously. The optimized content of H3 BO3 is 0.06 mol/mol. The particle size of the phosphor becomes large when the phosphor was synthesized using H3 BO3 as flux. H3 BO3 can effectively reduce the energy barrier and make more Eu2+ and Nd3+ enter
449
crystal lattice. Thus, the luminescent center ions and the density of traps become large, which make the afterglow properties better. Acknowledgements The authors would like to thank the National Hi-Tech R&D Program of China (863 Program, No. 2001AA324080) and the National Natural Science Foundation of China (No. 50204002). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
V. Abbruscato, J. Electrochem. Soc. 118 (6) (1971) 930–933. Y. Murayam, Ceram. Jpn. 32 (1) (1997) 40–43. M. Tang, C. Li, Z. Gao, Chin. J. Lumin. 16 (1) (1995) 51–56 (in Chinese). J. H¨ols¨a, H. Jungner, M. Lastusaari, J. Niittykoski, J. Alloys. Compd. 323–324 (2001) 326–330. T. Zhang, Q. Su, S. Wang, Chin. J. Lumin. 20 (1999) 170–175 (in Chinese). H. Yamamoto, T. Matsuzawa, J. Lumin. 72–74 (1997) 287–289. X. Teng, W. Zhuang, C. Zhao, H. Zhao, Y. Fang, Y. Chang, Y. Sun, J. Rare Earths 22 (3) (2004) 412–416 (in Chinese). J. Niittykoski, T. Aitasalo, J. H¨ols¨a, H. Jungner, M. Lastusaari, M. Parkkinen, M. Tukia, J. Alloys. Compd. 374 (2004) 108–111. Y. Li, Rare earth 19 (3) (1998) 68–72. D. Wang, M. Wang, Mater. Sci. Eng. 16 (4) (1998) 40–43. N. Abanti, T.R.N. Kutty, J. Alloys. Compd. 354 (2003) 221–231. I.-C. Chen, T.-M. Chen, J. Mater. Res. 16 (3) (2001) 644–651. Q. Song, M. Wu, J. Chen, Chin. J. Lumin. 12 (2) (1991) 144–149 (in Chinese). Z. Xiao, Light-storage Luminescent Materials and their products, Chemical Industry Press, 2002, pp. 112–114 (in Chinese). Y. Zhai, X. Zhang, J. Li, Y. Tian, J. Rare Earths 21 (2) (2003) 207–209 (in Chinese).
Effect of flux on the properties of CaAl2O4:Eu2+, Nd3+ long afterglow phosphor Xiaoming Teng, Weidong Zhuang ∗ , Yunsheng Hu, Chunlei Zhao, Huaqiang He, Xiaowei Huang National Engineering Research Center for Rare Earth Materials, General Research Institute for Nonferrous Metals, and Grirem Advanced Materials Co. Ltd., Beijing 100088, China Received 12 October 2006; received in revised form 27 March 2007; accepted 1 April 2007 Available online 6 April 2007
Abstract The long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ was prepared by high temperature solid-state reaction method under reducing atmosphere. The effect of flux H3 BO3 on the crystal structure and luminescent properties of the phosphor was studied. Results of XRD indicate that the volume of unit cell becomes smaller, and then the crystal field is changed, which results in the easier transition of 4f-5d. On the other hand, H3 BO3 addition is in favor of the formation of pure phase CaAl2 O4 . Both behaviors enhance the emission intensity of the obtained phosphor to some extent. But its emission peak does not shift evidently because the energy level difference of 4f-5d does not be changed obviously. Moreover, H3 BO3 also affects the afterglow properties of this phosphor. The optimized content of H3 BO3 is 0.06 mol/mol for the obtained phosphor with excellent properties. © 2007 Elsevier B.V. All rights reserved. Keywords: Rare earth; Long afterglow; Aluminate; Flux
1. Introduction
2. Experimental
The aluminate long afterglow phosphor has characteristics of high luminescent brightness, long afterglow time, good chemical stability, no pollutions, etc. So the aluminate long afterglow phosphor is widely applied in luminescent paint, night illumination, instrumental display, etc. [1–4]. The studies of aluminate system mainly have focused on doping with the second activator except Eu since 1990s, such as Dy, Nd, etc. It is hoped that the phosphor can form the proper trap energy level via doping microelement, thereby achieve the aim that enhance luminescent brightness and prolong afterglow time [5–7]. At the same time, the effect of flux on synthetic techniques and luminescent properties has become one of the hotspot in the aluminate luminescent materials activated by rare earth [8–11]. Chen et al. [12] studied the effect of B2 O3 on the properties of SrAl2 O4 :Eu2+ , Dy3+ prepared by sol–gel method. However, the action and mechanism of H3 BO3 in the phosphor are not clear completely. In this paper, the effect of flux H3 BO3 on structure and property of long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ has been studied by XRD, SEM, spectra and long afterglow properties.
The long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ was prepared by the high temperature solid-state reaction method. CaCO3 (3N), Al2 O3 (4N), Eu2 O3 (4N), Nd2 O3 (4N) were used as raw materials. Small quantities of H3 BO3 were introduced as flux. The mixture of raw materials was ground and then sintered at 1350 ◦ C for about 3 h under reducing atmosphere. The sample was cooled, grinded and sieved, and then the aluminate long afterglow phosphor CaAl2 O4 :Eu2+ , Nd3+ was obtained. The afterglow brightness and time of the phosphor were measured by a ST-900PM photometer. Its excitation and emission spectra were detected by FluoroMax-II spectrofluorometer made in the United States. The crystal structure of the phosphor was checked using a MXP21VAHF-M21X X-ray diffractometer that was manufactured in Japan. The SEM analysis was conducted on JSM-6400 Scanning Electron Microscope made in Japan. Horiba LA-300 laser scattering particle size analyzer was used to characterize the particle size of this phosphor.
∗
Corresponding author. Tel.: +86 10 89583430 15; fax: +86 10 89583430 20. E-mail address: [email protected] (W. Zhuang).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.013
3. Results and discussion 3.1. X-ray diffraction analysis Fig. 1 shows XRD patterns of CaAl2 O4 :Eu2+ , Nd3+ long afterglow phosphor prepared with H3 BO3 as flux (a) and without H3 BO3 (b). By analyzing these diffractive peaks, it is easy to find that the CaAl2 O4 phase was produced fully. However, there are still some CaAl4 O7 impurity phases. The CaAl4 O7 will contam-
X. Teng et al. / Journal of Alloys and Compounds 458 (2008) 446–449
447
Fig. 1. The XRD patterns of CaAl2 O4 :Eu2+ , Nd3+ prepared with H3 BO3 as flux (a) and without H3 BO3 (b). (“o” belong to CaAl4 O7 impure phase, other diffraction peaks belong to CaAl2 O4 phase).
inate the luminescence of this phosphor. The addition of H3 BO3 has decreased the impure phase of CaAl4 O7 in this phosphor, which enhances the initial brightness and prolongs afterglow time of this phosphor to some extent. When the phosphor is doped with H3 BO3 as flux, parts of B entering crystal lattice replace Al. However, large parts of B do not enter crystal lattice, which melt at low temperature and act as flux for the synthesis of the phosphor. It is suitable for producing pure phase and easy to hold integrality of crystal due to the low melting point of the compound. B which do not enter crystal lattice are help to urge activator ions entering crystal lattice and form luminescent center and trap center, which is easier to obtain single phase of CaAl2 O4 . 3.2. SEM analysis
Fig. 2. SEM photos of the phosphor synthesized with H3 BO3 as flux (a) and without H3 BO3 (b).
Fig. 2 is the SEM photos of the phosphor synthesized with H3 BO3 as flux (a) and without H3 BO3 (b). Table 1 lists the particle size of the phosphor. Obviously, the particle size of phosphor synthesized without H3 BO3 is smaller. While H3 BO3 was added to reaction system as flux, H3 BO3 participates in the solidstate reaction and quickens the rate of reaction. Liquid interfaces are produced among crystal grains, and then the crystal grains reunite and result in the bigger particle size. 3.3. Spectra analysis Fig. 3 is the emission spectra of the phosphor synthesized with H3 BO3 as flux and without H3 BO3 (λex = 365 nm). The emission spectra show a broadband emission peak from Eu2+ , which is Table 1 Particle size of the phosphor synthesized with H3 BO3 as flux and without H3 BO3 Sample
D10 (m)
D50 (m)
D90 (m)
No flux H3 BO3
3.07 6.22
19.71 30.74
79.55 97.43
Fig. 3. Emission spectra of CaAl2 O4 :Eu2+ , Nd3+ synthesized with H3 BO3 as flux (a) and without H3 BO3 (b).
448
X. Teng et al. / Journal of Alloys and Compounds 458 (2008) 446–449
Table 2 Cell parameters of the phosphor synthesized with H3 BO3 as flux and without H3 BO3 Sample
a (nm)
b (nm)
c (nm)
V (nm3 )
No flux H3 BO3
0.8697 0.8691
0.8090 0.8082
1.5211 1.5208
1.0702 1.0682
due to the transition of Eu2+ that originates from 4f6 5d excitation state to 4f7 ground state. As shown in Fig. 3, the position of the emission peak does not change when the phosphor is doped with H3 BO3 as flux, which is centered at about 440 nm. But the emission intensity of the phosphor prepared with H3 BO3 is much higher than that of the phosphor prepared without H3 BO3 . Generally, the luminescence of CaAl2 O4 :Eu2+ , Nd3+ originates from the 4f-5d electron transition of Eu2+ . When the crystal field is changed, the energy difference between 4f-5d electron will change accordingly, which will lead to the shift of emission peak [11]. However, the emission spectra in Fig. 3 show the position of emission peak does not change evidently when the phosphor was synthesized with H3 BO3 as flux. It is explained that the crystal field surroundings of Eu2+ are not changed too much after B is introduced in the lattice. On the other hand, the crystal cell volume of CaAl2 O4 is 1.0691 nm3 (shown in Table 2). It has the trend to become small compared with that of synthesized without H3 BO3 . Its crystal cell volume is 1.0702 nm3 . When part of Al is replaced by B, the crystal is distorted because the radius of B is smaller than that of Al. The distortion may result in the easier 4f-5d transition of Eu2+ , and then the intensity of luminescence becomes stronger. At the same time, the reaction temperature is reduced due to H3 BO3 addition, which makes the reaction process completely and promotes the formation of pure phase CaAl2 O4 . Both behaviors enhance the emission intensity of the phosphor. 3.4. Effect of the content of H3 BO3 Figs. 4 and 5 show the effect of different content of H3 BO3 on long afterglow properties of CaAl2 O4 :Eu2+ , Nd3+ . Obviously, when the content of H3 BO3 is 0.06 mol/mol, the initial brightness of the phosphor is the best and the afterglow time is the longest. However, the luminescent properties of the phosphor become bad when the content of H3 BO3 continues to increase. 3.5. Mechanism of long afterglow luminescence and action of H3 BO3 In general, the long afterglow aluminate phosphor excited by Eu2+ can produce some trap energy levels with different depth due to doping with other rare earth ions, and thus prolong afterglow time [13,14]. Under 365 nm UV-excitation, the luminescence process of Eu2+ includes two parts: one is that the electrons at the excited state return ground state, and the other is that the electrons in trap energy level release to excitation state and then return ground state due to the thermal disturbance. The first part of luminescence does not exist after the excitation is stopped. The electrons
Fig. 4. Effect of the content of H3 BO3 on the initial brightness of CaAl2 O4 :Eu2+ , Nd3+ .
Fig. 5. The decay curve of CaAl2 O4 :Eu2+ , Nd3+ synthesized with different content of H3 BO3 (a, x = 0; b, x = 0.03; c, x = 0.06; d, x = 0.09 mol/mol).
captured and storaged at the trap energy level will be excited to 4f6 5d excitation state with the help of thermal disturbance, and then the electrons return 8 S7/2 ground state in succession, which leads to the characteristic luminescence of Eu2+ (shown in Fig. 6). The number of electrons storaged in the trap energy level is high density, and its depth is proper to releasing electrons at room temperature. So the phosphor possesses high afterglow brightness and long afterglow time [14,15].
Fig. 6. Mechanism of long afterglow luminescence in CaAl2 O4 :Eu2+ , Nd3+ .
X. Teng et al. / Journal of Alloys and Compounds 458 (2008) 446–449
However, the action of H3 BO3 is different from the abovementioned reason. When Eu2+ and Nd3+ replace Ca2+ , the crystal lattice produces distortion and the phosphor has higher energy barrier. When the phosphor is doped with H3 BO3 , B2 O3 has higher reaction activation energy, which can effectively reduce the energy barrier and make more Eu2+ and Nd3+ enter crystal lattice. Thus, the luminescent center ions and the density of traps become large. The afterglow properties of aluminate phosphor doped with rare earth ions have great connection with the lattice defect. The deeper the trap depth and the larger the density are, the better the afterglow properties are. Furthermore, when the phosphor is doped with H3 BO3 , the electron traps become deeper because the electronegativity of B is larger than Al and the radius of B is smaller than Al. So the afterglow properties of the CaAl2 O4 :Eu2+ , Nd3+ phosphor become better. 4. Conclusion The CaAl2 O4 :Eu2+ , Nd3+ phosphor was successfully synthesized by conventional solid-state reaction method. The addition of H3 BO3 as flux is in favor of formation of CaAl2 O4 pure phase, which enhances the intensity of emission of the phosphor. The position of the emission peak does not change evidently because the energy level difference of 4f-5d does not be changed obviously. The optimized content of H3 BO3 is 0.06 mol/mol. The particle size of the phosphor becomes large when the phosphor was synthesized using H3 BO3 as flux. H3 BO3 can effectively reduce the energy barrier and make more Eu2+ and Nd3+ enter
449
crystal lattice. Thus, the luminescent center ions and the density of traps become large, which make the afterglow properties better. Acknowledgements The authors would like to thank the National Hi-Tech R&D Program of China (863 Program, No. 2001AA324080) and the National Natural Science Foundation of China (No. 50204002). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
V. Abbruscato, J. Electrochem. Soc. 118 (6) (1971) 930–933. Y. Murayam, Ceram. Jpn. 32 (1) (1997) 40–43. M. Tang, C. Li, Z. Gao, Chin. J. Lumin. 16 (1) (1995) 51–56 (in Chinese). J. H¨ols¨a, H. Jungner, M. Lastusaari, J. Niittykoski, J. Alloys. Compd. 323–324 (2001) 326–330. T. Zhang, Q. Su, S. Wang, Chin. J. Lumin. 20 (1999) 170–175 (in Chinese). H. Yamamoto, T. Matsuzawa, J. Lumin. 72–74 (1997) 287–289. X. Teng, W. Zhuang, C. Zhao, H. Zhao, Y. Fang, Y. Chang, Y. Sun, J. Rare Earths 22 (3) (2004) 412–416 (in Chinese). J. Niittykoski, T. Aitasalo, J. H¨ols¨a, H. Jungner, M. Lastusaari, M. Parkkinen, M. Tukia, J. Alloys. Compd. 374 (2004) 108–111. Y. Li, Rare earth 19 (3) (1998) 68–72. D. Wang, M. Wang, Mater. Sci. Eng. 16 (4) (1998) 40–43. N. Abanti, T.R.N. Kutty, J. Alloys. Compd. 354 (2003) 221–231. I.-C. Chen, T.-M. Chen, J. Mater. Res. 16 (3) (2001) 644–651. Q. Song, M. Wu, J. Chen, Chin. J. Lumin. 12 (2) (1991) 144–149 (in Chinese). Z. Xiao, Light-storage Luminescent Materials and their products, Chemical Industry Press, 2002, pp. 112–114 (in Chinese). Y. Zhai, X. Zhang, J. Li, Y. Tian, J. Rare Earths 21 (2) (2003) 207–209 (in Chinese).