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Synthesis and luminescence properties of europium doped YBa3B9O18
Physica B 407 (2012) 2725–2728
Contents lists available at SciVerse ScienceDirect
Physica B journal homepage: www.elsevier.com/locate/physb
Synthesis and luminescence properties of europium doped YBa3B9O18 Ming He a, G.L Huang b, H.L. Tao b, Z.H. Zhang b,n a b
Department of Physics, Dalian Jiaotong University, Dalian 116028, China Liaoning Key Materials Laboratory for Railway, School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, China
a r t i c l e i n f o
abstract
Article history: Received 26 September 2011 Received in revised form 17 January 2012 Accepted 31 March 2012 Available online 6 April 2012
Europium (Eu3 þ ) doped YBa3B9O18 were synthesized by conventional solid state solidification methods. (Y1 xEux)Ba3B9O18 formed solid solutions in the range of x ¼ 0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu3 þ excitation and emission. The charge transfer excitation band of Eu3 þ dominates the excitation spectra. The emission spectrum of Eu3 þ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the 5D0 level to the levels 7FJ (J ¼0, 1, 2, 3, 4) of Eu3 þ ions. The dependence of luminescence intensity on Eu3 þ concentration shows no concentration quenching for fully concentrated EuBa3B9O18. Eu3 þ doped YBa3B9O18 are promising phosphors for applications in displays and optical devices. & 2012 Elsevier B.V. All rights reserved.
Keywords: Y(1 x)EuxBa3B9O18 Solid state solidification methods Luminescence properties
1. Introduction In recent years, great efforts have been made to develop new light-emitting devices and luminescence materials. Among these, a number of researches have been carried out on the investigation of the crystal chemistry and the luminescence properties of borates, because many of these compounds show nonlinear optical properties, high transmittance in the ultraviolet (UV) region, and large birefringence [1,2]. Generally, In order to improve the luminescence properties, the borates are doped with rare-earth elements, such as Eu3 þ or Ce3 þ [3,4]. Rare-earth impurities serve as luminescent centers in the crystals, with an emission wavelength in the range of 300–600 nm. Detection of this wavelength is efficient and easy with today’s photomultiplier tubes. However, it is well known that a low doping of Eu3 þ in a compound leads to a weak luminescence, while heavy doping causes the ‘‘concentration quenching’’ of the luminescence[5]. If the rare-earth ions were spaced out by relatively large anionic groups (such as BO3, B3O6, PO4, or WO4, etc.), the concentration quenching process would scarcely occur [6]. Thus it is very important to find a proper host material with anionic group (used to restrict the concentration quenching process) for exploiting new luminescence materials. YBa3B9O18, one of isostructural compounds REBa3B9O18 (REEu, Gd, Tb, Lu) [7], adopts a centric space group P63/m with lattice ˚ Each B atom is bonded parameters a ¼7.1761 A˚ and c¼16.9657 A. to three O atoms, and three BO3 groups form a planar hexagonal [B3O6]3 ring. These planar rings are parallel to each other and
n
Corresponding author. Tel.: þ86 411 84105700; fax: þ86 411 84109417. E-mail address: [email protected] (Z.H. Zhang).
0921-4526/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physb.2012.03.076
stack along the c-axis in the unit cell, with regular YO6 octahedra and irregular BaO6 and BaO9 polyhedra in between the hexagonal [B3O6]3 rings. Because of the planar hexagonal [B3O6]3 rings in YBa3B9O18 lattices, perhaps it might act as a potential host material for a new luminescence material through rare-earth ions doping. In this paper, we report the synthesis and luminescence properties of europium doped YBa3B9O18. The dependence of luminescence intensity on Eu3 þ concentration shows no concentration quenching processes were observed, which imply that YBa3B9O18 is an excellent host materials and may find potential applications in displays and optical devices.
2. Experiments Polycrystalline europium doped YBa3B9O18 powder was synthesized from analytical reagents: Eu2O3, Y2O3, BaCO3, and H3BO3. About 1% mol excess H3BO3 was added to compensate for the B2O3 volatilization in the solid-state reactions. The mixtures were sintered at 400 1C for 1 h to let BaCO3 and H3BO3 decomposed slowly, and then calcined 850 1C for 3 day with intermediate grindings. The as-prepared samples were checked by powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). The X-ray diffraction data of the polycrystals were collected on an X-ray Rigaku diffractometer D/Max-2400 with Cu K radiation (40 kV, 140 mA) at room temperature. The emission and excitation spectra were recorded using a Hitchi-F4500-FL spectrofluorometer equipped with a xenon lamp. The X-ray excited luminescence of the samples was examined under room temperature using an X-ray excited spectrometer.
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3. Results and discussions Shown in Fig. 1(a) is the theoretical XRD pattern for YBa3B9O18. Fig. 1(b)–(d) are the selected measured XRD patterns for the synthesized Y(1 x)EuxBa3B9O18 materials with Eu doping concentrations x¼ 0.1, 0.4, 0.8, respectively. It is found that the experimental results agree well with the calculated result and no impurity phases were detected. Eu-doping does not modify the structure of YBa3B9O18, accounting for the similar atomic radius of Eu and Y atoms. Solid solutions are formed in the whole range (x¼0 1.0) for the system Y(1 x)EuxBa3B9O18. Fig. 2(a) shows the typical SEM photograph of the synthesized Y(1 x)EuxBa3B9O18 materials. The layered structure was observed and the prominent characteristic of Y(1 x)EuxBa3B9O18 crystal growth is the serious anisotropic growth rate. The growth rate along the ab plane is –5 times larger than that along the c-axis. This phenomenon can be easily understood from the periodic bond chain (PBC) theory (The fundamental building units in the structure, planar hexagonal [B3O6]3 [8] are parallel to each other and form the so-called F faces). [9] The local chemical compositions of the samples are further characterized by energy dispersive X-ray spectroscopy (EDS). Fig. 2(b) shows the typical EDS results, revealing the existence of Y, Ba, B, O and Eu in the samples. In each of the samples, the EDS have been performed on several different locations and similar chemical compositions are identified, which suggest uniform distribution of the doped Eu3 þ ions. Luminescence properties of Eu3 þ ions in YBa3B9O18 are studied upon excitation in ultraviolet–visible range. Fig. 3(a) shows the excitation spectrum obtained by monitoring the 5D0-7F1 at 589 nm (the excitation spectra are similar for the samples with different doping concentrations). The main broad band at 200–300 nm originates from the charge transfer (CT) transition of O-Eu3 þ [10]. Namely, the electron delocalized from the filled 2p shell of O2 to the partially filled 4f shell of Eu3 þ . The intensity of the CT band is
Fig. 2. (a) Typical SEM image of the samples, indicating the layered structures; (b) Typical EDX results, revealing the existence of Y, Ba, B, O and Eu in the samples.
Fig. 1. (a) XRD pattern of the calculated YBa3B9O18; (b)–(d) The measured XRD patterns of Y(1 x)EuxBa3B9O18 (x ¼0.1, 0.4, 0.8), respectively.
much stronger than the lines between 300 nm and 450 nm due to the f-f transitions of Eu3 þ ions. Fig. 3(b) shows the emission spectra for Y0.8Eu0.2Ba3B9O18 (lex ¼229 nm). It was found that the Eu3 þ doped YBa3B9O18 samples presented the characteristic Eu3 þ luminescence, that is, the emission of Eu3 þ ions in YBa3B9O18 extends from 550 nm to 720 nm and consists mainly of several groups of lines. These emission features are due to the transitions from the excited state 5D0 to the ground states 7FJ (J¼0, 1, 2, 3, 4) in the 4f6 configuration of Eu3 þ ions [6,11]. The emission spectra dominated by main lines at around 589 nm are attributed to the magnetic dipole transition of 5D0-7F1 and main lines at –610 nm due to 5 D0-7F2 transition (electric dipole transition). The ratios of the red emission at –610 nm to the orange one at –589 nm (abbreviated as the R/O value) are all lower than 1.00 for different Eu3 þ contents. Therefore, the orange emission is predominant and Eu3 þ does occupy the inversion symmetry sites in the host lattices according to the Judd–Ofelt theory [12]. Except the transition from 5D0, no emission from the higher level, e.g., 5D1,2, was detected, because the low-lying charge-transfer states skips the higher-lying 5DJ levels during the relaxation process [13]. Considering 2Jþ 1 components for Eu3 þ in a crystal field, the maximum splitting numbers of transition lines for 5D0-7FJ (J¼ 0, 1, 2) are 1(for J¼ 0), 3 (for J¼1) and 5 (for J¼2) for each site [14]. From the emission spectrum shown in Fig. 3(b), one peak at 578 nm (5D0-7F0), three lines for 5D0-7F1, and five lines for 5D0-7F2 are observed. It is suggested that the Eu3 þ ions are doped into YBa3B9O18 matrix in one crystallographic site, which is consistent with the crystal structure of YBa3B9O18 [7]. The
M. He et al. / Physica B 407 (2012) 2725–2728
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Fig. 4. Luminescence intensities (lex ¼ 229 nm, lem ¼589 nm) of Y(1 x)EuxBa3B9 O18 as a function of Eu3 þ concentration.
Fig. 3. (a) Excitation spectra recorded in the range from 200 nm to 450 nm under emission at 589 nm. (b) Emission spectrum obtained in the range from 500 nm to 720 nm when excited at 229 nm.
dependence of luminescence intensity (5D0-7F1 transition of Eu3 þ , lex ¼229 nm) on the Eu3 þ concentration is shown in Fig. 4. The intensity of the emission peak is increasing with the increment of Eu3 þ ions concentration in the main, so no obvious concentration quenching processes were observed. The luminescence properties of Eu3 þ doped YBa3B9O18 were investigated at the high-energy excitation (X-rays). Fig. 5 shows the X-ray excited emission for Y(1 x)EuxBa3B9O18 with different Eu3 þ concentrations. Two main peaks with the peak center at –589 nm and –610 nm are observed, which is different from the broad emission band observed in host material YBa3B9O18 [15]. Eu3 þ ions are the most important element for efficient X-ray excited luminescence in Y(1 x)EuxBa3B9O18 (the luminescence of YBa3B9O18 is caused by the structural feature of BO3 group). The energy was absorbed by the B–O groups and then transferred to Eu3 þ ions, thus the transitions from the excited state to the ground states of Eu3 þ ions occurred. The experiments results reveal that, under the excitation of X-ray, the luminescent intensity of EuBa3B9O18 is the highest through x¼0–1. YBa3B9O18 is a potential X-ray phosphor with a light yield 15% as large as that of bismuth germanate BGO[15]. For comparison, we measured the X-ray excited luminescence spectra of YBa3B9O18 and EuBa3B9O18 under same excitation wavelength and intensity. The result is shown in Fig. 6, we can see that the light intensity of EuBa3B9O18(lem ¼ 589 nm) is about 17 times as large as that of YBa3B9O18 (lem ¼ 380 nm). 589 nm lies in the spectral range
Fig. 5. X-ray excited luminescence of Y(1 x)EuxBa3B9O18 (x¼ 0.1, 0.4, 1.0).
Fig. 6. X-ray excited luminescence spectra of YBa3B9O18 and EuBa3B9O18 under same excitation wavelength and intensity.
matching most popular photomultiplier tubes(PMT), so EuBa3B9O18 is also an efficient X-ray phosphor and may find applications in X-ray imaging or detection.
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4. Conclusions Europium (Eu3 þ ) doped YBa3B9O18 were synthesized by solidstate reaction at high temperature. Y(1 x)EuxBa3B9O18 formed solid solutions in the range of x ¼0–1.0. The excitation spectra of these systems (lem ¼589 nm) showed an intense broad band with maximum at 229 nm related to the O-Eu3 þ charge transfer state. The emission spectrum of Eu3 þ ions consists mainly of several groups of lines in the 550–750 nm region, due to the transitions from the 5D0 level to the levels 7FJ (J ¼0, 1, 2, 3, 4) of Eu3 þ ions. The dependence of luminescence intensity on Eu3 þ concentration was studied in detail, which shows no obvious concentration quenching processes. X-ray excited luminescence indicates that EuBa3B9O18 is a potential efficient X-ray phosphor. Acknowledgment The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China (Grant No. 50902014 and 51002017).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
M. He, X.L. Chen, H. Okudera, A. Simon, Chem. Mater. 17 (2005) 2193. L. Wu, X.L. Chen, H. Li, M. He, Y.P. Xu, X.Z. Li, Inorg. Chem. 44 (2005) 6409. G. Zhao, X. Zeng, J. Xu, Y. Zhou, J. Cryst. Growth 253 (2003) 290. L. Pidol, A. Kahn-Harari, B. Viana, B. Ferrand, P. Dorenbos, J.T.M. deHass, C.W.E. van Eijk, E. Virey, J. Phys. Condens. Matter 15 (2003) 2091. F. Kellendonk, G. Blasse, Phys. Status Solidi B 108 (1981) 541. V.P. Dotsenko, I.V. Berezovskaya, N.P. Efryushina, A.S. Voloshinovskii, G.B. Stryganyuk, J. Mater. Sci. 45 (2010) 1469. X.Z. Li, C. Wang, X.L. Chen, H. Li, L.S. Jia, L. Wu, Y.X. Du, Y.P. Xu, Inorg. Chem. 43 (2004) 8555. M. He, W.Y. Wang, Y.P. Sun, Y.P. Xu, X.L. Chen, J. Cryst. Growth 307 (2007) 427. P. Hartman, W.G. Perdok, Acta Crystallogr. 8 (1955) 49. A. Cla´udia Kodaira, F. Hermi Brito, F.C. Maria Cla´udia Felinto, J. Solid State Chem. 171 (2003) 401. O. Aloui-Lebbou, C. Goutaudier, S. Kubota, C. Dujardin, M. Cohen-Adad, C. Pedrini, P. Florian, D. Massiot, Opt. Mater. 16 (2001) 77. J. Huang, L. Zhou, Q. Pang, F. Gong, J. Sun, W. Wang, Luminescence 24 (2009) 363. W.H. Fonger, C.W. Struck, J Chem. Phys. 52 (12) (1970) 6364. N. Xie, Y. Huang, X. Qiao, L. Shi, H. Seo, Mater. lett. 64 (2010) 1000. C.J. Duan, J.L. Yuan, J.T. Zhao, J. Solid State Chem. 178 (2005) 3698.
Contents lists available at SciVerse ScienceDirect
Physica B journal homepage: www.elsevier.com/locate/physb
Synthesis and luminescence properties of europium doped YBa3B9O18 Ming He a, G.L Huang b, H.L. Tao b, Z.H. Zhang b,n a b
Department of Physics, Dalian Jiaotong University, Dalian 116028, China Liaoning Key Materials Laboratory for Railway, School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, China
a r t i c l e i n f o
abstract
Article history: Received 26 September 2011 Received in revised form 17 January 2012 Accepted 31 March 2012 Available online 6 April 2012
Europium (Eu3 þ ) doped YBa3B9O18 were synthesized by conventional solid state solidification methods. (Y1 xEux)Ba3B9O18 formed solid solutions in the range of x ¼ 0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu3 þ excitation and emission. The charge transfer excitation band of Eu3 þ dominates the excitation spectra. The emission spectrum of Eu3 þ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the 5D0 level to the levels 7FJ (J ¼0, 1, 2, 3, 4) of Eu3 þ ions. The dependence of luminescence intensity on Eu3 þ concentration shows no concentration quenching for fully concentrated EuBa3B9O18. Eu3 þ doped YBa3B9O18 are promising phosphors for applications in displays and optical devices. & 2012 Elsevier B.V. All rights reserved.
Keywords: Y(1 x)EuxBa3B9O18 Solid state solidification methods Luminescence properties
1. Introduction In recent years, great efforts have been made to develop new light-emitting devices and luminescence materials. Among these, a number of researches have been carried out on the investigation of the crystal chemistry and the luminescence properties of borates, because many of these compounds show nonlinear optical properties, high transmittance in the ultraviolet (UV) region, and large birefringence [1,2]. Generally, In order to improve the luminescence properties, the borates are doped with rare-earth elements, such as Eu3 þ or Ce3 þ [3,4]. Rare-earth impurities serve as luminescent centers in the crystals, with an emission wavelength in the range of 300–600 nm. Detection of this wavelength is efficient and easy with today’s photomultiplier tubes. However, it is well known that a low doping of Eu3 þ in a compound leads to a weak luminescence, while heavy doping causes the ‘‘concentration quenching’’ of the luminescence[5]. If the rare-earth ions were spaced out by relatively large anionic groups (such as BO3, B3O6, PO4, or WO4, etc.), the concentration quenching process would scarcely occur [6]. Thus it is very important to find a proper host material with anionic group (used to restrict the concentration quenching process) for exploiting new luminescence materials. YBa3B9O18, one of isostructural compounds REBa3B9O18 (REEu, Gd, Tb, Lu) [7], adopts a centric space group P63/m with lattice ˚ Each B atom is bonded parameters a ¼7.1761 A˚ and c¼16.9657 A. to three O atoms, and three BO3 groups form a planar hexagonal [B3O6]3 ring. These planar rings are parallel to each other and
n
Corresponding author. Tel.: þ86 411 84105700; fax: þ86 411 84109417. E-mail address: [email protected] (Z.H. Zhang).
0921-4526/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physb.2012.03.076
stack along the c-axis in the unit cell, with regular YO6 octahedra and irregular BaO6 and BaO9 polyhedra in between the hexagonal [B3O6]3 rings. Because of the planar hexagonal [B3O6]3 rings in YBa3B9O18 lattices, perhaps it might act as a potential host material for a new luminescence material through rare-earth ions doping. In this paper, we report the synthesis and luminescence properties of europium doped YBa3B9O18. The dependence of luminescence intensity on Eu3 þ concentration shows no concentration quenching processes were observed, which imply that YBa3B9O18 is an excellent host materials and may find potential applications in displays and optical devices.
2. Experiments Polycrystalline europium doped YBa3B9O18 powder was synthesized from analytical reagents: Eu2O3, Y2O3, BaCO3, and H3BO3. About 1% mol excess H3BO3 was added to compensate for the B2O3 volatilization in the solid-state reactions. The mixtures were sintered at 400 1C for 1 h to let BaCO3 and H3BO3 decomposed slowly, and then calcined 850 1C for 3 day with intermediate grindings. The as-prepared samples were checked by powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). The X-ray diffraction data of the polycrystals were collected on an X-ray Rigaku diffractometer D/Max-2400 with Cu K radiation (40 kV, 140 mA) at room temperature. The emission and excitation spectra were recorded using a Hitchi-F4500-FL spectrofluorometer equipped with a xenon lamp. The X-ray excited luminescence of the samples was examined under room temperature using an X-ray excited spectrometer.
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3. Results and discussions Shown in Fig. 1(a) is the theoretical XRD pattern for YBa3B9O18. Fig. 1(b)–(d) are the selected measured XRD patterns for the synthesized Y(1 x)EuxBa3B9O18 materials with Eu doping concentrations x¼ 0.1, 0.4, 0.8, respectively. It is found that the experimental results agree well with the calculated result and no impurity phases were detected. Eu-doping does not modify the structure of YBa3B9O18, accounting for the similar atomic radius of Eu and Y atoms. Solid solutions are formed in the whole range (x¼0 1.0) for the system Y(1 x)EuxBa3B9O18. Fig. 2(a) shows the typical SEM photograph of the synthesized Y(1 x)EuxBa3B9O18 materials. The layered structure was observed and the prominent characteristic of Y(1 x)EuxBa3B9O18 crystal growth is the serious anisotropic growth rate. The growth rate along the ab plane is –5 times larger than that along the c-axis. This phenomenon can be easily understood from the periodic bond chain (PBC) theory (The fundamental building units in the structure, planar hexagonal [B3O6]3 [8] are parallel to each other and form the so-called F faces). [9] The local chemical compositions of the samples are further characterized by energy dispersive X-ray spectroscopy (EDS). Fig. 2(b) shows the typical EDS results, revealing the existence of Y, Ba, B, O and Eu in the samples. In each of the samples, the EDS have been performed on several different locations and similar chemical compositions are identified, which suggest uniform distribution of the doped Eu3 þ ions. Luminescence properties of Eu3 þ ions in YBa3B9O18 are studied upon excitation in ultraviolet–visible range. Fig. 3(a) shows the excitation spectrum obtained by monitoring the 5D0-7F1 at 589 nm (the excitation spectra are similar for the samples with different doping concentrations). The main broad band at 200–300 nm originates from the charge transfer (CT) transition of O-Eu3 þ [10]. Namely, the electron delocalized from the filled 2p shell of O2 to the partially filled 4f shell of Eu3 þ . The intensity of the CT band is
Fig. 2. (a) Typical SEM image of the samples, indicating the layered structures; (b) Typical EDX results, revealing the existence of Y, Ba, B, O and Eu in the samples.
Fig. 1. (a) XRD pattern of the calculated YBa3B9O18; (b)–(d) The measured XRD patterns of Y(1 x)EuxBa3B9O18 (x ¼0.1, 0.4, 0.8), respectively.
much stronger than the lines between 300 nm and 450 nm due to the f-f transitions of Eu3 þ ions. Fig. 3(b) shows the emission spectra for Y0.8Eu0.2Ba3B9O18 (lex ¼229 nm). It was found that the Eu3 þ doped YBa3B9O18 samples presented the characteristic Eu3 þ luminescence, that is, the emission of Eu3 þ ions in YBa3B9O18 extends from 550 nm to 720 nm and consists mainly of several groups of lines. These emission features are due to the transitions from the excited state 5D0 to the ground states 7FJ (J¼0, 1, 2, 3, 4) in the 4f6 configuration of Eu3 þ ions [6,11]. The emission spectra dominated by main lines at around 589 nm are attributed to the magnetic dipole transition of 5D0-7F1 and main lines at –610 nm due to 5 D0-7F2 transition (electric dipole transition). The ratios of the red emission at –610 nm to the orange one at –589 nm (abbreviated as the R/O value) are all lower than 1.00 for different Eu3 þ contents. Therefore, the orange emission is predominant and Eu3 þ does occupy the inversion symmetry sites in the host lattices according to the Judd–Ofelt theory [12]. Except the transition from 5D0, no emission from the higher level, e.g., 5D1,2, was detected, because the low-lying charge-transfer states skips the higher-lying 5DJ levels during the relaxation process [13]. Considering 2Jþ 1 components for Eu3 þ in a crystal field, the maximum splitting numbers of transition lines for 5D0-7FJ (J¼ 0, 1, 2) are 1(for J¼ 0), 3 (for J¼1) and 5 (for J¼2) for each site [14]. From the emission spectrum shown in Fig. 3(b), one peak at 578 nm (5D0-7F0), three lines for 5D0-7F1, and five lines for 5D0-7F2 are observed. It is suggested that the Eu3 þ ions are doped into YBa3B9O18 matrix in one crystallographic site, which is consistent with the crystal structure of YBa3B9O18 [7]. The
M. He et al. / Physica B 407 (2012) 2725–2728
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Fig. 4. Luminescence intensities (lex ¼ 229 nm, lem ¼589 nm) of Y(1 x)EuxBa3B9 O18 as a function of Eu3 þ concentration.
Fig. 3. (a) Excitation spectra recorded in the range from 200 nm to 450 nm under emission at 589 nm. (b) Emission spectrum obtained in the range from 500 nm to 720 nm when excited at 229 nm.
dependence of luminescence intensity (5D0-7F1 transition of Eu3 þ , lex ¼229 nm) on the Eu3 þ concentration is shown in Fig. 4. The intensity of the emission peak is increasing with the increment of Eu3 þ ions concentration in the main, so no obvious concentration quenching processes were observed. The luminescence properties of Eu3 þ doped YBa3B9O18 were investigated at the high-energy excitation (X-rays). Fig. 5 shows the X-ray excited emission for Y(1 x)EuxBa3B9O18 with different Eu3 þ concentrations. Two main peaks with the peak center at –589 nm and –610 nm are observed, which is different from the broad emission band observed in host material YBa3B9O18 [15]. Eu3 þ ions are the most important element for efficient X-ray excited luminescence in Y(1 x)EuxBa3B9O18 (the luminescence of YBa3B9O18 is caused by the structural feature of BO3 group). The energy was absorbed by the B–O groups and then transferred to Eu3 þ ions, thus the transitions from the excited state to the ground states of Eu3 þ ions occurred. The experiments results reveal that, under the excitation of X-ray, the luminescent intensity of EuBa3B9O18 is the highest through x¼0–1. YBa3B9O18 is a potential X-ray phosphor with a light yield 15% as large as that of bismuth germanate BGO[15]. For comparison, we measured the X-ray excited luminescence spectra of YBa3B9O18 and EuBa3B9O18 under same excitation wavelength and intensity. The result is shown in Fig. 6, we can see that the light intensity of EuBa3B9O18(lem ¼ 589 nm) is about 17 times as large as that of YBa3B9O18 (lem ¼ 380 nm). 589 nm lies in the spectral range
Fig. 5. X-ray excited luminescence of Y(1 x)EuxBa3B9O18 (x¼ 0.1, 0.4, 1.0).
Fig. 6. X-ray excited luminescence spectra of YBa3B9O18 and EuBa3B9O18 under same excitation wavelength and intensity.
matching most popular photomultiplier tubes(PMT), so EuBa3B9O18 is also an efficient X-ray phosphor and may find applications in X-ray imaging or detection.
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4. Conclusions Europium (Eu3 þ ) doped YBa3B9O18 were synthesized by solidstate reaction at high temperature. Y(1 x)EuxBa3B9O18 formed solid solutions in the range of x ¼0–1.0. The excitation spectra of these systems (lem ¼589 nm) showed an intense broad band with maximum at 229 nm related to the O-Eu3 þ charge transfer state. The emission spectrum of Eu3 þ ions consists mainly of several groups of lines in the 550–750 nm region, due to the transitions from the 5D0 level to the levels 7FJ (J ¼0, 1, 2, 3, 4) of Eu3 þ ions. The dependence of luminescence intensity on Eu3 þ concentration was studied in detail, which shows no obvious concentration quenching processes. X-ray excited luminescence indicates that EuBa3B9O18 is a potential efficient X-ray phosphor. Acknowledgment The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China (Grant No. 50902014 and 51002017).
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