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Luminescence properties of Ce3+-doped and Ce3+–Tb3+ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED
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Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED Jie Donga, Lei Wanga,b, Cai'e Cuia,b, Yue Tiana,b, Ping Huanga,b,n a Physics and Optoelectronic Engineering College, Taiyuan University of Technology, Taiyuan 030024, China Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, China
b
Received 19 August 2014; received in revised form 10 September 2014; accepted 10 September 2014
Abstract Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 (NCASO) phosphors have been synthesized via a high temperature solidstate reaction method. The samples were measured by using X-ray diffraction (XRD), photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The results of XRD indicated that the as-prepared samples were pure NCASO phosphors. The Ce3 þ -doped NCASO phosphor exhibited an intense blue emission centered at 414 nm under 335 nm excitation. The optimal doping concentration of Ce3 þ in NCASO was confirmed 0.75 mol%. The concentration quenching occurs beyond 0.75 mol% of Ce3 þ because of electric quadrupole–quadrupole interaction between Ce3 þ ions. To tune the luminescent color of NCASO:Ce3 þ phosphor, Tb3 þ ions were introduced into the lattice of NCASO:Ce3 þ phosphor. It was found the emission intensity of Ce3 þ ions decreases gradually with the increase of Tb3 þ ions concentration owing to energy transfer from Ce3 þ to Tb3 þ . Moreover, the emitting colors can be adjusting from blue to green. The electric dipole–dipole interaction was induced to be responsible for energy transfer between Ce3 þ to Tb3 þ . These results show that NCASO:Ce3 þ , Tb3 þ phosphors can be used as a potential single-phased white-emitting candidate for UV WLEDs. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Phosphor; Na0.34Ca0.66Al1.66Si2.34O8; WLEDs; Energy transfer
1. Introduction Nowadays, light-emitting diodes (LEDs) have attracted much interest due to their superior features, such as energy saving, longer lifetime and environmental friendliness [1–3]. The most common method to generate white light-emitting diodes (WLEDs) is a combination of a blue InGaN chip with a yellow emitting phosphor (YAG:Ce3 þ ). However, the application faces several disadvantages, such as low color-rendering index (CRI 70–80) and high correlated color temperature (CCT 7750 K) due to the lack of a red-emitting component [1,4], and color drift by different drive conditions [5]. Therefore, it has been developed by the n Corresponding author at: Physics and Optoelectronic Engineering College, Taiyuan University of Technology, Taiyuan 030024, China. Tel.: þ 86 0351 4175345. E-mail address: [email protected] (P. Huang).
combination of near-ultraviolet (NUV) LEDs or ultraviolet (UV) LEDs with red-, green-, and blue-emitting phosphors to improve the CRI and tune the CCT value. But this type of WLEDs has low luminescence efficiency because of the reabsorption of the blue emission by red and green phosphors [6], and there is also a high cost issue to produce such devices [7]. Therefore, a single-phased full-color emitting phosphor upon UV-LED chip is considered to be potentially useful due to stability, small color aberration and low cost [8]. The method to generate a single-phased white-lightemitting phosphor is co-doping sensitizer and activator into one host lattice by using an efficient possibility of energy transfer from sensitizer to activator [9,10]. As we know, Tb3 þ ions shows sharp lines at 488, 543, and 582 nm, and so it could be an ideal emitting activator for phosphors [11]. However Tb3 þ ion shows very week emission under UV excitation because of forbidden f–f absorption transitions. Therefore it is necessary to find a sensitizer to enhance the emission intensity of Tb3 þ ions based on the principle of
http://dx.doi.org/10.1016/j.ceramint.2014.09.066 0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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energy transfer. The luminescence properties of Ce3 þ -doped phosphors can be excited by NUV sources due to 5d–4f transitions of Ce3 þ ion, and exhibits broad emission and excitation band [12]. So it could be an important sensitizer to overcome the drawbacks mentioned above. In recent years, because of the excellent luminescence properties such as stable crystal structure and high chemical stability [13,14], aluminosillcate-based phosphors have drawn much attention. The Na0.34Ca0.66Al1.66Si2.34O8:Eu2 þ phosphor had been reported firstly by Lee [15], which is included in the plagioclase feidspar crystal structure based on the aluminosilicate composition shows the excellent thermal stability [16–21]. However, there has no report about the optical property of Ce3 þ and Tb3 þ and energy transfer from Ce3 þ to Tb3 þ in the NCASO host. In this paper, a single-phased phosphor NCASO:Ce3 þ , Tb3 þ has been prepared via the high temperature solid-state reaction method. The strong absorption of the NCASO:Ce3 þ , Tb3 þ phosphor in the range of 250–380 nm suggests that it has great potential for WLED. Moreover, the luminescence properties as well as the energy transfer mechanism from Ce3 þ to Tb3 þ ions of the phosphors are investigated according to the PL spectra and energy transfer efficiency. 2. Experimental Na0.34Ca0.66 xAl1.66Si2.34O8:xCe3 þ (x=0–0.015) and Na0.34 Ca0.6525 yAl1.66Si2.34O8:0.0075Ce3 þ , yTb3 þ (y=0.002–0.012) phosphors were synthesized by the high temperature solidstate reaction method (x and y represent the concentration of Ce3 þ and Tb3 þ , respectively). The starting materials were Na2CO3 (99.8%), CaCO3 (99%), Al2O3 (99.99%), SiO2 (99.99%), CeO2 (99%), Tb4O7 (99.99%). They were weighed in stoichiometric amounts and ground thoroughly in an agate mortar for 1 h. Then, the mixtures were fired in alumina crucibles at 1300 1C for 2 h under CO reducing atmosphere. After cooling to room temperature in the furnace, the samples were ground again to obtain the final phosphors. The X-ray diffraction (XRD) data of the samples were carried out by X-ray Power diffraction at 40 kV and 30 mA with a Shimadzu-6000 X-ray generator with Cu Kα (λ=0.15406 nm) radiation and the scan step was 0.0021. Photoluminescence excitation (PLE) and emission (PL) spectra were characterized by using an F-280 fluorescence spectrophotometer with a 150 W Xe lamp as excitation source. All of the measurements were performed at room temperature. 3. Results and discussion 3.1. Phase characterization The powder XRD patterns of Na0.34Ca0.6525Al1.66Si2.34 O8:0.0075Ce3 þ and Na0.34Ca0.6425Al1.66Si2.34O8:0.0075Ce3 þ , 0.01Tb3 þ phosphors are shown in Fig. 1. All of the profiles match well with the Joint Committee for Powder Diffraction Standard file 86-1650 for NCASO. No additional XRD peaks are found, indicating that the as-prepared samples are pure NCASO phosphors. In the crystal structure of NCASO
Fig. 1. XRD patterns of NCASO:0.0075Ce3 þ and NCASO:0.0075Ce3 þ , 0.01Tb3 þ .
phosphor, Na þ and Ca2 þ ions occupy the same sites. The Na þ /Ca2 þ ions have four different cases of coordination environments (Na þ /Ca2 þ -1, Na þ /Ca2 þ -2, and Na þ /Ca2 þ -4 are 8-coordinated; Na þ /Ca2 þ -3 is 10-coordinated) [22]. Typically, effective radii (r) of cations change depending on the coordination number (CN) [23]. In the view of effective ionic radii, Ce3 þ ions and Tb3 þ ions are expected to occupy the Na þ /Ca2 þ share sites preferably, because the ionic radius of Ce3 þ ions (1.14 Å) and Tb3 þ ions (0.92 Å for CN ¼ 6, 1.04 Å for CN ¼ 8) is close to those of Ca2 þ ions (1.12 Å for CN ¼ 8, 1.23 Å for CN ¼ 10) and Na þ ions (1.18 Å for CN ¼ 8, 1.24 Å for CN ¼ 9, 1.39 Å for CN ¼ 12) [15,25]. 3.2. The photoluminescence properties of NCASO:Ce3 þ phosphor Fig. 2 shows the photoluminescence (PL) spectra and photoluminescence excitation (PLE) spectra of the Na0.34 Ca0.66 xAl1.66Si2.34O8:xCe3 þ phosphors with different Ce3 þ concentrations (x¼ 0.25, 0.5, 0.75, 1, 1.25, 1.5 mol%). It can be seen that the PLE spectra of Fig. 2(a) monitored at 414 nm show a broad absorption band ranged from 240 to 380 nm. It corresponds to the 4f–5d transition of Ce3 þ ions[24]. The excitation peak moves to longer wavelength with increasing the Ce3 þ concentration. The PL spectra under the excitation of 335 nm are presented in Fig. 2(b). Under 335 nm excitation, the emission spectra shows a broad blue–green emission band extending from 375 nm to 550 nm with a maximum at about 414 nm which corresponds to the 5d–4f transition of Ce3 þ . It is observed that the PL intensity is affected by Ce3 þ concentration. With the increase of Ce3 þ ions concentration, the emission intensity increases and reaches a maximum at x¼ 0.0075. Subsequently, the emission intensity falls down with further increasing x, suggesting that concentration quenching occurs. Also, the emission peak is red-shifted as increasing Ce3 þ concentration. That is because of there are four substitutional sites of Na þ /Ca2 þ ions for Ce3 þ ions. With the increase of doping concentration of Ce3 þ , the relative intensity among the four different Ce3 þ ions emission changed, and the energy transfer occurred among Ce3 þ ions [15]. Consequently, the emission peak is slightly changed and red-shifted in the crystal structure.
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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between I and x is plotted in Fig. 3. The value of θ is 10.23, which is approximately equal to 10. This result indicates that the main mechanism of concentration quenching of NCASO:Ce3 þ is quadrupole–quadrupole interactions. 3.3. Optical properties and energy transfer in NCASO:Ce3 þ , Tb3 þ Fig. 4 shows the PL and PLE spectra of three samples, namely Ce3 þ singly doped NCASO:0.0075Ce3 þ (a), Tb3 þ singly doped NCASO:0.01Tb3 þ (b), and Ce3 þ , Tb3 þ doubly doped NCASO:0.0075Ce3 þ , 0.01Tb3 þ (c), respectively. The PLE spectrum of Tb3 þ singly doped sample monitored at 544 nm contains several lines in the region from 200 to 400 nm centered at 243 nm, which corresponds to absorption f–f transition of the Tb3 þ ions. PL spectrum exhibits two groups of emission of Tb3 þ upon 243 nm excitation, as shown in Fig. 4(b). One group is the shorter transition emissions of 5D3–7FJ (J¼ 5, 4, 3) located at about 420, 440, 470 nm, and the other consist of several bands located at 489, 544, 585, and 625 nm, corresponding to the 5 D4–7FJ (J¼ 6, 5, 4, 3) transitions, respectively [31]. It could be seen from Fig. 4(a) and (b) that NCASO:Tb3 þ shows very week emission under UV excitation compared with NCASO:Ce3 þ due to forbidden f–f absorption transitions of Tb3 þ ions. Moreover,
Fig. 2. Excitation (a) and emission (b) spectra of NCASO:xCe3 þ (x¼ 0.25, 0.5, 0.75, 1, 1.25, 1.5 mol%) phosphors with different Ce3 þ concentrations.
It is accepted that the concentration quenching originates from energy transfer among the activator ions. Thus, the critical distance of energy transfer (Rc) should be taken into consideration. It could be calculated by the following formula developed by Blasse [25]: 3V 1=3 Rc 2 ð1Þ 4πxc N where V is the volume of the unit cell, xc is the critical concentration of Ce3 þ ions, and N is the number of formula units in the unit cell. For the NCASO host, V ¼ 1345.2825 Å3, xc ¼ 0.0075, and N ¼ 8. Hence, Rc is calculated to be 34.99 Å. There are two types of energy transfer: one is exchange interaction and the other is electrostatic interaction [26]. In the case of the exchange interaction, the critical distance should be shorter than 3–4 Å [27]. It indicates that the energy transfer process is not controlled by exchange interaction but by electrostatic interaction [28]. The electrostatic interaction type including dipole–dipole, dipole–quadrupole and quadrupole–quadrupole can be calculated by Eq. (2) [29]: h i1 I ¼ k 1 þ βðxÞθ=3 ð2Þ x where I/x is the emission intensity (I) per activator concentration (x), k and β are constants for the same excitation condition and θ¼ 6, 8, 10 for dipole–dipole (d–d), dipole–quadrupole (d–q) and quadrupole–quadrupole (q–q), respectively [30]. The relationship
Fig. 3. Relation between the I and x of Ce3 þ in NCASO:xCe3 þ phosphors.
Fig. 4. PLE and PL spectra of NCASO:0.0075Ce3 þ (a), NCASO:0.01Tb3 þ (b) and NCASO:0.0075Ce3 þ , 0.01Tb3 þ (c) phosphors.
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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there is a spectral overlap between the emission band of the Ce3 þ ions and the excitation band of the Tb3 þ ions, indicating an efficient possibility of energy transfer from Ce3 þ to Tb3 þ ions [32]. In Fig. 4(c), it is clearly exhibited that the PLE spectrum monitored at 544 nm of Tb3 þ is similar to that monitored at 414 nm of Ce3 þ , demonstrating the existence of energy transfer from Ce3 þ to Tb3 þ in NCASO. And it is another evidence for the energy transfer in NCASO:Ce3 þ , Tb3 þ that the emission intensity of Tb3 þ is considerably enhanced. The PLE spectra show a broad band range from 250 to 380 nm which means that the NCASO:Ce3 þ , Tb3 þ phosphor is a potential phosphor for WLEDs. The PL spectra of NCASO:0.0075Ce3 þ , yTb3 þ phosphors with different Tb3 þ concentrations (y¼ 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 mol%) under 340 nm excitation are shown in Fig. 5. With the Tb3 þ ions concentration increases, the emission intensity of Tb3 þ ions at 544 nm increases and reaches a maximum when y¼ 0.01. Then, as a result of concentration quenching effect, the emission intensity of Tb3 þ tends to decrease. The emission intensity of Ce3 þ at 414 nm was simultaneously found to decrease. These results further support the energy transfer process from Ce3 þ to Tb3 þ in NCASO. Generally, energy transfer efficiency (ηT) can be described according to the formula [33]
where ISO is the luminescence intensities of the Ce3 þ in the absence of the Tb3 þ ions and IS is the luminescence intensities of the Ce3 þ in the presence of the Tb3 þ ions. Fig. 6 displays the energy transfer efficiency (ηT) as a function of Tb3 þ content. It is shown that the energy transfer efficiency (ηT) of NCASO:0.0075Ce3 þ , yTb3 þ phosphor increase gradually with the increasing of Tb3 þ concentration. On the basis of Dexter's energy transfer formula for multipolar interaction and Reisfeld's approximation, the following relation can be obtained [34,35]: η0 p C n=3 η
ð4Þ
where η0 and η are the luminescence quantum efficiency of the donor (Ce3 þ ) in the absence and presence of the acceptor (Tb3 þ ). The value of η0/η can be approximately calculated by the ratio of relative luminescence intensities [34,35] I0 p Cn=3 I
ð5Þ
Fig. 5. PL spectra of NCASO:0.0075Ce3 þ , yTb3 þ phosphors with different Tb3 þ concentrations at the excitation wavelength of 340 nm.
where I0 is the intrinsic luminescence intensity of Ce3 þ and I is the luminescence intensity of Ce3 þ with the presence of Tb3 þ , and C is the content of Tb3 þ , n=6, 8, and 10 correspond to dipole–dipole, dipole–quadrupole, and quadrupole–quadrupole interactions, respectively. The I0/I Cn/3 plots are represented in Fig. 7 and a linear relation is observed when n¼ 6. It indicates that the energy transfer mechanism between Ce3 þ and Tb3 þ ions is dipole–dipole interaction in NCASO:Ce3 þ , Tb3 þ phosphor. Fig. 8 shows the CIE chromaticity diagram for NCASO: 0.0075Ce3 þ , yTb3 þ phosphors excited at 360 nm. It is found that the color tone of the phosphors can be tuned from blue to white and eventually to green with increasing the doping content of Tb3 þ ions. However its chromaticity coordinates are not very close to the standard white (0.33, 0.33) due to lack of a red-emitting band. Because it exhibits a strong absorption in the near-UV spectral region and near-white-light emission, NCASO:0.0075Ce3 þ , yTb3 þ phosphors can be used as a potential white-emitting candidate for UV LEDs. Table 1 illustrates the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of NCASO:0.0075Ce3 þ , yTb3 þ phosphors under 360 nm excitation.
Fig. 6. Dependence of the energy transfer efficiency (ηT) on the Tb3 þ content.
Fig. 7. Dependence of I0/I of Ce3 þ on (a) C6/3, (b) C8/3, and (c) C10/3.
ηT ¼ 1
IS I SO
ð3Þ
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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Institutions of Shanxi, Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi and school fund of Taiyuan University of Technology (tyut-rc201159a). References
Fig. 8. CIE chromaticity diagram of NCASO:0.0075Ce3 þ , yTb3 þ phosphors under 360 nm excitation.
Table 1 The Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of NCASO:0.0075Ce3 þ , yTb3 þ phosphors under 360 nm excitation. Point No. in chromaticity diagram
Tb3 þ concentrations
(x, y)
A B C D E F G
0 0.002 0.004 0.006 0.008 0.010 0.012
(0.165, (0.174, (0.184, (0.194, (0.204, (0.207, (0.221,
0.090) 0.128) 0.168) 0.205) 0.243) 0.256) 0.306)
4. Conclusions In summary, a series of blue-emitting phosphors NCASO:Ce3 þ and single-phased emission-tunable NCASO:0.0075Ce3 þ , Tb3 þ have been successfully synthesized by the solid-state reaction method. Pure phase of NCASO:Ce3 þ and NCASO:Ce3 þ , Tb3 þ can be obtained at 1300 1C for 2 h.The emission spectra of NCASO:Ce3 þ shows a strong broad blue emission band at about 414 nm which ascribes to the 5d–4f transition of Ce3 þ ions under 335 nm excitation. While the Ce3 þ ions concentration increases to 0.75 mol%, the NCASO:Ce3 þ has the highest emission intensity. Above the critical value, the emission intensity tends to decreased as a result of concentration quenching effect. An efficient energy transfer from the Ce3 þ to Tb3 þ ions can be achieved in the NCASO:Ce3 þ , Tb3 þ phosphors. Under 340 nm excitation, NCASO:Ce3 þ , Tb3 þ phosphor shows a broad emission band at 414 nm of Ce3 þ and an emission band at 544 nm of Tb3 þ . With the Tb3 þ ions concentrations increases, the color tone of the phosphors can be tuned from blue to white. Because the phosphor exhibits a strong excitation band from 250 to 380 nm, it can be a promising single-phased color-tunable phosphor for UV WLEDs. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (No. 51302182), the Natural Science Foundation of Shanxi Province (2013021004-2, 2014011017-3), Program for the Top Young Academic Leaders of Higher Learning
[1] S. Nakamura, G. Fasol, The Blue Laser Diode: GaN Based Light Emitters and Lasers, Springer, Berlin, New York, 1997. [2] E.F. Schubert, J.K. Kim, Solid-state light sources getting smart, Science 27 (2005) 1274–1278. [3] R.J. Xie, N. Hirosaki, M. Mitomo, K. Sakuma, N. Kinura, Wavelengthtunable and thermally stable Li-α-sialon: Eu2 þ oxynitride phosphors for white light-emitting diodes, Appl. Phys. Lett. 89 (2006) 241103. [4] Y. Narukawa, I. Niki, K. Izuno, M. Yamada, Y. Murazaki, T. Mukai, Phosphor-conversion white light emitting diode using InGaN nearultraviolet chip, Jpn. J. Appl. Phys. 41 (2002) L371–L373. [5] Y. Xu, L. Chen, Y. Li, G. Song, Y. Wang, W. Zhuang, Z. Long, Phosphor-conversion white light using InGaN ultraviolet laser diode, Appl. Phys. Lett. 92 (2008) 021129. [6] Y. Uchida, T. Taguchi, Lighting theory and luminous characteristics of white light-emitting diodes, Opt. Eng. 44 (2005) 124003. [7] Y.H. Won, H.S. Jang, W.B. Im, J.S. Lee, D.Y. Jeon, Tunable full-coloremitting La0.827Al11.9O19.09:Eu2 þ , Mn2 þ phosphor for application to warm white-light-emitting diodes, Appl. Phys. Lett. 89 (2006) 231909. [8] W. Lü, Z. Hao, X. Zhang, Y. Luo, X. Wang, J. Zhang, Tunable full-color emitting BaMg2Al6Si9O30:Eu2 þ , Tb3 þ , Mn2 þ phosphors based on energy transfer, Inorg. Chem. 50 (2011) 7846–7851. [9] J.S. Kim, P.E. Jeonny, J.C. Choi, H.L. Park, S.I. Mho, G.C. Kim, Warmwhite-light emitting diode utilizing a single-phase full-color Ba3MgSi2O8: Eu2 þ , Mn2 þ phosphor, Appl. Phys. Lett. 84 (2004) 2931–2933. [10] K.H. Kwon, W.B. Im, H.S. Jang, H.S. Yoo, D.Y. Jeon, Luminescence properties and energy transfer of site-sensitive Ca6 x yMgx z(PO4)4:Euy 2 þ , Mnz 2 þ phosphors and their application to near-UV LED-based white LEDs, Inorg. Chem. 48 (2009) 11525–11532. [11] R.P. Rao, Tb3 þ activated green phosphors for plasma dosplay panel applications, J. Electrochem. Soc. 150 (2003) H165–H171. [12] J. Ruan, R. Xie, S. Funahashi, Y. Tanaka, T. Takeda, T. Suehiro, N. Hirosaki, Y. Li, A novel yellow-emitting SrAlSi4N7:Ce3 þ phosphor for solid state lighting: synthesis, electronic structure and photoluminescence properties, J. Solid State Chem. 208 (2013) 50–57. [13] X.Y. Yang, T.S. Tiam, X. Yu, H.V. Demir, X.W. Sun, Europium (II)doped microporous zeolite derivatives with enhanced photoluminescence by isolating active luminescence centers, ACS Appl. Mater. Interfaces 3 (2011) 4431–4436. [14] B. Wang, L. Sun, H. Ju, Luminescence and energy transfer of white-light emitting CaAl2SiO6:Ce3 þ ,Tb3 þ phosphors, Solid State Commun. 150 (2010) 1460–1462. [15] G.Y. Lee, J.Y. Han, W.B. Im, S.H. Cheong, D.Y. Jeon, Novel blueemitting NaxCa1 xAl2 xSi2 þ xO8:Eu2 þ (x ¼0.34) phosphor with high luminescent efficiency for UV-pumped light-emitting diodes, Inorg. Chem. 51 (2012) 10688–10694. [16] M.M. Krzmanc, M. Valant, B. Jancar, D. Suvorov, Sub-solidus synthesis and microwave dielectric characterization of plagioclase feldspars, J. Am. Ceram. Soc. 88 (2005) 2472–2479. [17] M.M. Krzmanc, M. Valant, D. Suvorov, A structural and dielectric characterization of NaxCa1 xAl2 xSi2 þ xO8 (x ¼0 and 1) ceramics, J. Eur. Ceram. Soc. 25 (2005) 2835–2838. [18] J.R. Smith, H.S. Yoder, Variations in X-ray powder diffraction patterns of plagioclase feldspars, Am. Mineral. 41 (1956) 632–647. [19] C.G. Cinnamon, S.W. Bailey, Antiphase domain structure of the intermediate composition plagioclase feldspars, Am. Mineral. 56 (1971) 1180–1198. [20] R.C. Doman, C.G. Cinnamon, S.W. Bailey, Structural discontinuities in the plagioclase feldspar series, Am. Mineral. 50 (1965) 724–740. [21] H. Kroll, W.F. Müller, X-ray and electron-optical investigation of synthetic high-temperature plagioclases, Phys. Chem. Miner. 5 (1980) 255–277.
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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J. Dong et al. / Ceramics International ] (]]]]) ]]]–]]]
[22] G.Y. Lee, W.B. Im, A. Kirakosyan, S.H. Cheong, J.Y. Han, D.Y. Jeon, Tunable emission from blue to white light in single-phase Na0.34Ca(0.66 x y)Al1.66Si2.34O8:xEu2 þ ,yMn2 þ (x¼ 0.07) phosphor for white-light UV LEDs, Opt. Express 21 (2013) 3287–3297. [23] R. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr. Sect. C – Struct. Chem. 32 (1976) 751–767. [24] G.N. Nikhare, S.C. Gedam, S.J. Dhoble, Photoluminescence and thermoluminescence of Ce3 þ ions doped in LiAl5O8 and NaAl11O17 aluminate systems, J. Lumin. 137 (2013) 290–295. [25] G. Blasse, Energy transfer between inequivalent Eu2 þ ions, J. Solid State Chem. 62 (1986) 207–211. [26] R. Reisfeld, E. Greenberg, R. Velapoldi, B. Barnett, Luminescence quantum efficiency of Gd and Tb in borate glasses and the mechanism of energy transfer between them, J. Chem. Phys. 56 (1972) 1698. [27] B.M. Antipeuko, I.M. Bataev, V.L. Ermolaev, T.A. Privalova, Ion-to-ion radiationless transfer of electron excitation energy between rare-earth ions in POCl3–SnCl4, Opt. Spektrosk. 29 (1970) 335. [28] D.L. Dexter, A theory of sensitized luminescence in solids, J. Chem. Phys. 21 (1953) 836–851.
[29] L. Ozawa, P.M. Jaffe, The mechanism of the emission color shift with activator concentration in Eu þ 3 activated phosphors, J. Electrochem. Soc. 118 (1971) 1678–1679. [30] L. Van Uitert, Characterization of energy transfer interactions between rare earth ions, J. Electrochem. Soc. 114 (1976) 1048–1053. [31] M. Weng, R. Yang, Y. Peng, J. Chen, Yellowish green-emitting KSrPO4: Tb3 þ phosphors with various doping concentrations prepared by using microwave assisted sintering, Ceram. Int. 38 (2012) 1319–1323. [32] G. Zhu, Y. Wang, Z. Ci, B. Liu, Y. Shi, S. Xin, Ca8Mg(SiO4)4Cl2:Ce3 þ , Tb3 þ : a potential single-phased phosphor for white-light-emitting diodes, J. Lumin. 132 (2012) 531–536. [33] J.C. Bourcet, F.K. Fong, Quantum efficiency of diffusion limited energy transfer in La1 x yCexTbyPO4, J. Chem. Phys. 60 (1974) 34. [34] D. Dexter, J.H. Schulman, Theory of concentration quenching in inorganic phosphors, J. Chem. Phys. 22 (1954) 1063. [35] R. Reisfeld, N. Lieblich-Soffer, Energy transfer from UO2 2 þ to Sm3 þ in phosphate glass, J. Solid State Chem. 28 (1979) 391–395.
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CERAMICS INTERNATIONAL
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Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED Jie Donga, Lei Wanga,b, Cai'e Cuia,b, Yue Tiana,b, Ping Huanga,b,n a Physics and Optoelectronic Engineering College, Taiyuan University of Technology, Taiyuan 030024, China Key Lab of Advanced Transducers and Intelligent Control System, Ministry of Education and Shanxi Province, Taiyuan University of Technology, Taiyuan 030024, China
b
Received 19 August 2014; received in revised form 10 September 2014; accepted 10 September 2014
Abstract Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 (NCASO) phosphors have been synthesized via a high temperature solidstate reaction method. The samples were measured by using X-ray diffraction (XRD), photoluminescence (PL) and photoluminescence excitation (PLE) spectra. The results of XRD indicated that the as-prepared samples were pure NCASO phosphors. The Ce3 þ -doped NCASO phosphor exhibited an intense blue emission centered at 414 nm under 335 nm excitation. The optimal doping concentration of Ce3 þ in NCASO was confirmed 0.75 mol%. The concentration quenching occurs beyond 0.75 mol% of Ce3 þ because of electric quadrupole–quadrupole interaction between Ce3 þ ions. To tune the luminescent color of NCASO:Ce3 þ phosphor, Tb3 þ ions were introduced into the lattice of NCASO:Ce3 þ phosphor. It was found the emission intensity of Ce3 þ ions decreases gradually with the increase of Tb3 þ ions concentration owing to energy transfer from Ce3 þ to Tb3 þ . Moreover, the emitting colors can be adjusting from blue to green. The electric dipole–dipole interaction was induced to be responsible for energy transfer between Ce3 þ to Tb3 þ . These results show that NCASO:Ce3 þ , Tb3 þ phosphors can be used as a potential single-phased white-emitting candidate for UV WLEDs. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Phosphor; Na0.34Ca0.66Al1.66Si2.34O8; WLEDs; Energy transfer
1. Introduction Nowadays, light-emitting diodes (LEDs) have attracted much interest due to their superior features, such as energy saving, longer lifetime and environmental friendliness [1–3]. The most common method to generate white light-emitting diodes (WLEDs) is a combination of a blue InGaN chip with a yellow emitting phosphor (YAG:Ce3 þ ). However, the application faces several disadvantages, such as low color-rendering index (CRI 70–80) and high correlated color temperature (CCT 7750 K) due to the lack of a red-emitting component [1,4], and color drift by different drive conditions [5]. Therefore, it has been developed by the n Corresponding author at: Physics and Optoelectronic Engineering College, Taiyuan University of Technology, Taiyuan 030024, China. Tel.: þ 86 0351 4175345. E-mail address: [email protected] (P. Huang).
combination of near-ultraviolet (NUV) LEDs or ultraviolet (UV) LEDs with red-, green-, and blue-emitting phosphors to improve the CRI and tune the CCT value. But this type of WLEDs has low luminescence efficiency because of the reabsorption of the blue emission by red and green phosphors [6], and there is also a high cost issue to produce such devices [7]. Therefore, a single-phased full-color emitting phosphor upon UV-LED chip is considered to be potentially useful due to stability, small color aberration and low cost [8]. The method to generate a single-phased white-lightemitting phosphor is co-doping sensitizer and activator into one host lattice by using an efficient possibility of energy transfer from sensitizer to activator [9,10]. As we know, Tb3 þ ions shows sharp lines at 488, 543, and 582 nm, and so it could be an ideal emitting activator for phosphors [11]. However Tb3 þ ion shows very week emission under UV excitation because of forbidden f–f absorption transitions. Therefore it is necessary to find a sensitizer to enhance the emission intensity of Tb3 þ ions based on the principle of
http://dx.doi.org/10.1016/j.ceramint.2014.09.066 0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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energy transfer. The luminescence properties of Ce3 þ -doped phosphors can be excited by NUV sources due to 5d–4f transitions of Ce3 þ ion, and exhibits broad emission and excitation band [12]. So it could be an important sensitizer to overcome the drawbacks mentioned above. In recent years, because of the excellent luminescence properties such as stable crystal structure and high chemical stability [13,14], aluminosillcate-based phosphors have drawn much attention. The Na0.34Ca0.66Al1.66Si2.34O8:Eu2 þ phosphor had been reported firstly by Lee [15], which is included in the plagioclase feidspar crystal structure based on the aluminosilicate composition shows the excellent thermal stability [16–21]. However, there has no report about the optical property of Ce3 þ and Tb3 þ and energy transfer from Ce3 þ to Tb3 þ in the NCASO host. In this paper, a single-phased phosphor NCASO:Ce3 þ , Tb3 þ has been prepared via the high temperature solid-state reaction method. The strong absorption of the NCASO:Ce3 þ , Tb3 þ phosphor in the range of 250–380 nm suggests that it has great potential for WLED. Moreover, the luminescence properties as well as the energy transfer mechanism from Ce3 þ to Tb3 þ ions of the phosphors are investigated according to the PL spectra and energy transfer efficiency. 2. Experimental Na0.34Ca0.66 xAl1.66Si2.34O8:xCe3 þ (x=0–0.015) and Na0.34 Ca0.6525 yAl1.66Si2.34O8:0.0075Ce3 þ , yTb3 þ (y=0.002–0.012) phosphors were synthesized by the high temperature solidstate reaction method (x and y represent the concentration of Ce3 þ and Tb3 þ , respectively). The starting materials were Na2CO3 (99.8%), CaCO3 (99%), Al2O3 (99.99%), SiO2 (99.99%), CeO2 (99%), Tb4O7 (99.99%). They were weighed in stoichiometric amounts and ground thoroughly in an agate mortar for 1 h. Then, the mixtures were fired in alumina crucibles at 1300 1C for 2 h under CO reducing atmosphere. After cooling to room temperature in the furnace, the samples were ground again to obtain the final phosphors. The X-ray diffraction (XRD) data of the samples were carried out by X-ray Power diffraction at 40 kV and 30 mA with a Shimadzu-6000 X-ray generator with Cu Kα (λ=0.15406 nm) radiation and the scan step was 0.0021. Photoluminescence excitation (PLE) and emission (PL) spectra were characterized by using an F-280 fluorescence spectrophotometer with a 150 W Xe lamp as excitation source. All of the measurements were performed at room temperature. 3. Results and discussion 3.1. Phase characterization The powder XRD patterns of Na0.34Ca0.6525Al1.66Si2.34 O8:0.0075Ce3 þ and Na0.34Ca0.6425Al1.66Si2.34O8:0.0075Ce3 þ , 0.01Tb3 þ phosphors are shown in Fig. 1. All of the profiles match well with the Joint Committee for Powder Diffraction Standard file 86-1650 for NCASO. No additional XRD peaks are found, indicating that the as-prepared samples are pure NCASO phosphors. In the crystal structure of NCASO
Fig. 1. XRD patterns of NCASO:0.0075Ce3 þ and NCASO:0.0075Ce3 þ , 0.01Tb3 þ .
phosphor, Na þ and Ca2 þ ions occupy the same sites. The Na þ /Ca2 þ ions have four different cases of coordination environments (Na þ /Ca2 þ -1, Na þ /Ca2 þ -2, and Na þ /Ca2 þ -4 are 8-coordinated; Na þ /Ca2 þ -3 is 10-coordinated) [22]. Typically, effective radii (r) of cations change depending on the coordination number (CN) [23]. In the view of effective ionic radii, Ce3 þ ions and Tb3 þ ions are expected to occupy the Na þ /Ca2 þ share sites preferably, because the ionic radius of Ce3 þ ions (1.14 Å) and Tb3 þ ions (0.92 Å for CN ¼ 6, 1.04 Å for CN ¼ 8) is close to those of Ca2 þ ions (1.12 Å for CN ¼ 8, 1.23 Å for CN ¼ 10) and Na þ ions (1.18 Å for CN ¼ 8, 1.24 Å for CN ¼ 9, 1.39 Å for CN ¼ 12) [15,25]. 3.2. The photoluminescence properties of NCASO:Ce3 þ phosphor Fig. 2 shows the photoluminescence (PL) spectra and photoluminescence excitation (PLE) spectra of the Na0.34 Ca0.66 xAl1.66Si2.34O8:xCe3 þ phosphors with different Ce3 þ concentrations (x¼ 0.25, 0.5, 0.75, 1, 1.25, 1.5 mol%). It can be seen that the PLE spectra of Fig. 2(a) monitored at 414 nm show a broad absorption band ranged from 240 to 380 nm. It corresponds to the 4f–5d transition of Ce3 þ ions[24]. The excitation peak moves to longer wavelength with increasing the Ce3 þ concentration. The PL spectra under the excitation of 335 nm are presented in Fig. 2(b). Under 335 nm excitation, the emission spectra shows a broad blue–green emission band extending from 375 nm to 550 nm with a maximum at about 414 nm which corresponds to the 5d–4f transition of Ce3 þ . It is observed that the PL intensity is affected by Ce3 þ concentration. With the increase of Ce3 þ ions concentration, the emission intensity increases and reaches a maximum at x¼ 0.0075. Subsequently, the emission intensity falls down with further increasing x, suggesting that concentration quenching occurs. Also, the emission peak is red-shifted as increasing Ce3 þ concentration. That is because of there are four substitutional sites of Na þ /Ca2 þ ions for Ce3 þ ions. With the increase of doping concentration of Ce3 þ , the relative intensity among the four different Ce3 þ ions emission changed, and the energy transfer occurred among Ce3 þ ions [15]. Consequently, the emission peak is slightly changed and red-shifted in the crystal structure.
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between I and x is plotted in Fig. 3. The value of θ is 10.23, which is approximately equal to 10. This result indicates that the main mechanism of concentration quenching of NCASO:Ce3 þ is quadrupole–quadrupole interactions. 3.3. Optical properties and energy transfer in NCASO:Ce3 þ , Tb3 þ Fig. 4 shows the PL and PLE spectra of three samples, namely Ce3 þ singly doped NCASO:0.0075Ce3 þ (a), Tb3 þ singly doped NCASO:0.01Tb3 þ (b), and Ce3 þ , Tb3 þ doubly doped NCASO:0.0075Ce3 þ , 0.01Tb3 þ (c), respectively. The PLE spectrum of Tb3 þ singly doped sample monitored at 544 nm contains several lines in the region from 200 to 400 nm centered at 243 nm, which corresponds to absorption f–f transition of the Tb3 þ ions. PL spectrum exhibits two groups of emission of Tb3 þ upon 243 nm excitation, as shown in Fig. 4(b). One group is the shorter transition emissions of 5D3–7FJ (J¼ 5, 4, 3) located at about 420, 440, 470 nm, and the other consist of several bands located at 489, 544, 585, and 625 nm, corresponding to the 5 D4–7FJ (J¼ 6, 5, 4, 3) transitions, respectively [31]. It could be seen from Fig. 4(a) and (b) that NCASO:Tb3 þ shows very week emission under UV excitation compared with NCASO:Ce3 þ due to forbidden f–f absorption transitions of Tb3 þ ions. Moreover,
Fig. 2. Excitation (a) and emission (b) spectra of NCASO:xCe3 þ (x¼ 0.25, 0.5, 0.75, 1, 1.25, 1.5 mol%) phosphors with different Ce3 þ concentrations.
It is accepted that the concentration quenching originates from energy transfer among the activator ions. Thus, the critical distance of energy transfer (Rc) should be taken into consideration. It could be calculated by the following formula developed by Blasse [25]: 3V 1=3 Rc 2 ð1Þ 4πxc N where V is the volume of the unit cell, xc is the critical concentration of Ce3 þ ions, and N is the number of formula units in the unit cell. For the NCASO host, V ¼ 1345.2825 Å3, xc ¼ 0.0075, and N ¼ 8. Hence, Rc is calculated to be 34.99 Å. There are two types of energy transfer: one is exchange interaction and the other is electrostatic interaction [26]. In the case of the exchange interaction, the critical distance should be shorter than 3–4 Å [27]. It indicates that the energy transfer process is not controlled by exchange interaction but by electrostatic interaction [28]. The electrostatic interaction type including dipole–dipole, dipole–quadrupole and quadrupole–quadrupole can be calculated by Eq. (2) [29]: h i1 I ¼ k 1 þ βðxÞθ=3 ð2Þ x where I/x is the emission intensity (I) per activator concentration (x), k and β are constants for the same excitation condition and θ¼ 6, 8, 10 for dipole–dipole (d–d), dipole–quadrupole (d–q) and quadrupole–quadrupole (q–q), respectively [30]. The relationship
Fig. 3. Relation between the I and x of Ce3 þ in NCASO:xCe3 þ phosphors.
Fig. 4. PLE and PL spectra of NCASO:0.0075Ce3 þ (a), NCASO:0.01Tb3 þ (b) and NCASO:0.0075Ce3 þ , 0.01Tb3 þ (c) phosphors.
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there is a spectral overlap between the emission band of the Ce3 þ ions and the excitation band of the Tb3 þ ions, indicating an efficient possibility of energy transfer from Ce3 þ to Tb3 þ ions [32]. In Fig. 4(c), it is clearly exhibited that the PLE spectrum monitored at 544 nm of Tb3 þ is similar to that monitored at 414 nm of Ce3 þ , demonstrating the existence of energy transfer from Ce3 þ to Tb3 þ in NCASO. And it is another evidence for the energy transfer in NCASO:Ce3 þ , Tb3 þ that the emission intensity of Tb3 þ is considerably enhanced. The PLE spectra show a broad band range from 250 to 380 nm which means that the NCASO:Ce3 þ , Tb3 þ phosphor is a potential phosphor for WLEDs. The PL spectra of NCASO:0.0075Ce3 þ , yTb3 þ phosphors with different Tb3 þ concentrations (y¼ 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 mol%) under 340 nm excitation are shown in Fig. 5. With the Tb3 þ ions concentration increases, the emission intensity of Tb3 þ ions at 544 nm increases and reaches a maximum when y¼ 0.01. Then, as a result of concentration quenching effect, the emission intensity of Tb3 þ tends to decrease. The emission intensity of Ce3 þ at 414 nm was simultaneously found to decrease. These results further support the energy transfer process from Ce3 þ to Tb3 þ in NCASO. Generally, energy transfer efficiency (ηT) can be described according to the formula [33]
where ISO is the luminescence intensities of the Ce3 þ in the absence of the Tb3 þ ions and IS is the luminescence intensities of the Ce3 þ in the presence of the Tb3 þ ions. Fig. 6 displays the energy transfer efficiency (ηT) as a function of Tb3 þ content. It is shown that the energy transfer efficiency (ηT) of NCASO:0.0075Ce3 þ , yTb3 þ phosphor increase gradually with the increasing of Tb3 þ concentration. On the basis of Dexter's energy transfer formula for multipolar interaction and Reisfeld's approximation, the following relation can be obtained [34,35]: η0 p C n=3 η
ð4Þ
where η0 and η are the luminescence quantum efficiency of the donor (Ce3 þ ) in the absence and presence of the acceptor (Tb3 þ ). The value of η0/η can be approximately calculated by the ratio of relative luminescence intensities [34,35] I0 p Cn=3 I
ð5Þ
Fig. 5. PL spectra of NCASO:0.0075Ce3 þ , yTb3 þ phosphors with different Tb3 þ concentrations at the excitation wavelength of 340 nm.
where I0 is the intrinsic luminescence intensity of Ce3 þ and I is the luminescence intensity of Ce3 þ with the presence of Tb3 þ , and C is the content of Tb3 þ , n=6, 8, and 10 correspond to dipole–dipole, dipole–quadrupole, and quadrupole–quadrupole interactions, respectively. The I0/I Cn/3 plots are represented in Fig. 7 and a linear relation is observed when n¼ 6. It indicates that the energy transfer mechanism between Ce3 þ and Tb3 þ ions is dipole–dipole interaction in NCASO:Ce3 þ , Tb3 þ phosphor. Fig. 8 shows the CIE chromaticity diagram for NCASO: 0.0075Ce3 þ , yTb3 þ phosphors excited at 360 nm. It is found that the color tone of the phosphors can be tuned from blue to white and eventually to green with increasing the doping content of Tb3 þ ions. However its chromaticity coordinates are not very close to the standard white (0.33, 0.33) due to lack of a red-emitting band. Because it exhibits a strong absorption in the near-UV spectral region and near-white-light emission, NCASO:0.0075Ce3 þ , yTb3 þ phosphors can be used as a potential white-emitting candidate for UV LEDs. Table 1 illustrates the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of NCASO:0.0075Ce3 þ , yTb3 þ phosphors under 360 nm excitation.
Fig. 6. Dependence of the energy transfer efficiency (ηT) on the Tb3 þ content.
Fig. 7. Dependence of I0/I of Ce3 þ on (a) C6/3, (b) C8/3, and (c) C10/3.
ηT ¼ 1
IS I SO
ð3Þ
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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Institutions of Shanxi, Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi and school fund of Taiyuan University of Technology (tyut-rc201159a). References
Fig. 8. CIE chromaticity diagram of NCASO:0.0075Ce3 þ , yTb3 þ phosphors under 360 nm excitation.
Table 1 The Commission Internationale de L'Eclairage (CIE) chromaticity coordinates of NCASO:0.0075Ce3 þ , yTb3 þ phosphors under 360 nm excitation. Point No. in chromaticity diagram
Tb3 þ concentrations
(x, y)
A B C D E F G
0 0.002 0.004 0.006 0.008 0.010 0.012
(0.165, (0.174, (0.184, (0.194, (0.204, (0.207, (0.221,
0.090) 0.128) 0.168) 0.205) 0.243) 0.256) 0.306)
4. Conclusions In summary, a series of blue-emitting phosphors NCASO:Ce3 þ and single-phased emission-tunable NCASO:0.0075Ce3 þ , Tb3 þ have been successfully synthesized by the solid-state reaction method. Pure phase of NCASO:Ce3 þ and NCASO:Ce3 þ , Tb3 þ can be obtained at 1300 1C for 2 h.The emission spectra of NCASO:Ce3 þ shows a strong broad blue emission band at about 414 nm which ascribes to the 5d–4f transition of Ce3 þ ions under 335 nm excitation. While the Ce3 þ ions concentration increases to 0.75 mol%, the NCASO:Ce3 þ has the highest emission intensity. Above the critical value, the emission intensity tends to decreased as a result of concentration quenching effect. An efficient energy transfer from the Ce3 þ to Tb3 þ ions can be achieved in the NCASO:Ce3 þ , Tb3 þ phosphors. Under 340 nm excitation, NCASO:Ce3 þ , Tb3 þ phosphor shows a broad emission band at 414 nm of Ce3 þ and an emission band at 544 nm of Tb3 þ . With the Tb3 þ ions concentrations increases, the color tone of the phosphors can be tuned from blue to white. Because the phosphor exhibits a strong excitation band from 250 to 380 nm, it can be a promising single-phased color-tunable phosphor for UV WLEDs. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (No. 51302182), the Natural Science Foundation of Shanxi Province (2013021004-2, 2014011017-3), Program for the Top Young Academic Leaders of Higher Learning
[1] S. Nakamura, G. Fasol, The Blue Laser Diode: GaN Based Light Emitters and Lasers, Springer, Berlin, New York, 1997. [2] E.F. Schubert, J.K. Kim, Solid-state light sources getting smart, Science 27 (2005) 1274–1278. [3] R.J. Xie, N. Hirosaki, M. Mitomo, K. Sakuma, N. Kinura, Wavelengthtunable and thermally stable Li-α-sialon: Eu2 þ oxynitride phosphors for white light-emitting diodes, Appl. Phys. Lett. 89 (2006) 241103. [4] Y. Narukawa, I. Niki, K. Izuno, M. Yamada, Y. Murazaki, T. Mukai, Phosphor-conversion white light emitting diode using InGaN nearultraviolet chip, Jpn. J. Appl. Phys. 41 (2002) L371–L373. [5] Y. Xu, L. Chen, Y. Li, G. Song, Y. Wang, W. Zhuang, Z. Long, Phosphor-conversion white light using InGaN ultraviolet laser diode, Appl. Phys. Lett. 92 (2008) 021129. [6] Y. Uchida, T. Taguchi, Lighting theory and luminous characteristics of white light-emitting diodes, Opt. Eng. 44 (2005) 124003. [7] Y.H. Won, H.S. Jang, W.B. Im, J.S. Lee, D.Y. Jeon, Tunable full-coloremitting La0.827Al11.9O19.09:Eu2 þ , Mn2 þ phosphor for application to warm white-light-emitting diodes, Appl. Phys. Lett. 89 (2006) 231909. [8] W. Lü, Z. Hao, X. Zhang, Y. Luo, X. Wang, J. Zhang, Tunable full-color emitting BaMg2Al6Si9O30:Eu2 þ , Tb3 þ , Mn2 þ phosphors based on energy transfer, Inorg. Chem. 50 (2011) 7846–7851. [9] J.S. Kim, P.E. Jeonny, J.C. Choi, H.L. Park, S.I. Mho, G.C. Kim, Warmwhite-light emitting diode utilizing a single-phase full-color Ba3MgSi2O8: Eu2 þ , Mn2 þ phosphor, Appl. Phys. Lett. 84 (2004) 2931–2933. [10] K.H. Kwon, W.B. Im, H.S. Jang, H.S. Yoo, D.Y. Jeon, Luminescence properties and energy transfer of site-sensitive Ca6 x yMgx z(PO4)4:Euy 2 þ , Mnz 2 þ phosphors and their application to near-UV LED-based white LEDs, Inorg. Chem. 48 (2009) 11525–11532. [11] R.P. Rao, Tb3 þ activated green phosphors for plasma dosplay panel applications, J. Electrochem. Soc. 150 (2003) H165–H171. [12] J. Ruan, R. Xie, S. Funahashi, Y. Tanaka, T. Takeda, T. Suehiro, N. Hirosaki, Y. Li, A novel yellow-emitting SrAlSi4N7:Ce3 þ phosphor for solid state lighting: synthesis, electronic structure and photoluminescence properties, J. Solid State Chem. 208 (2013) 50–57. [13] X.Y. Yang, T.S. Tiam, X. Yu, H.V. Demir, X.W. Sun, Europium (II)doped microporous zeolite derivatives with enhanced photoluminescence by isolating active luminescence centers, ACS Appl. Mater. Interfaces 3 (2011) 4431–4436. [14] B. Wang, L. Sun, H. Ju, Luminescence and energy transfer of white-light emitting CaAl2SiO6:Ce3 þ ,Tb3 þ phosphors, Solid State Commun. 150 (2010) 1460–1462. [15] G.Y. Lee, J.Y. Han, W.B. Im, S.H. Cheong, D.Y. Jeon, Novel blueemitting NaxCa1 xAl2 xSi2 þ xO8:Eu2 þ (x ¼0.34) phosphor with high luminescent efficiency for UV-pumped light-emitting diodes, Inorg. Chem. 51 (2012) 10688–10694. [16] M.M. Krzmanc, M. Valant, B. Jancar, D. Suvorov, Sub-solidus synthesis and microwave dielectric characterization of plagioclase feldspars, J. Am. Ceram. Soc. 88 (2005) 2472–2479. [17] M.M. Krzmanc, M. Valant, D. Suvorov, A structural and dielectric characterization of NaxCa1 xAl2 xSi2 þ xO8 (x ¼0 and 1) ceramics, J. Eur. Ceram. Soc. 25 (2005) 2835–2838. [18] J.R. Smith, H.S. Yoder, Variations in X-ray powder diffraction patterns of plagioclase feldspars, Am. Mineral. 41 (1956) 632–647. [19] C.G. Cinnamon, S.W. Bailey, Antiphase domain structure of the intermediate composition plagioclase feldspars, Am. Mineral. 56 (1971) 1180–1198. [20] R.C. Doman, C.G. Cinnamon, S.W. Bailey, Structural discontinuities in the plagioclase feldspar series, Am. Mineral. 50 (1965) 724–740. [21] H. Kroll, W.F. Müller, X-ray and electron-optical investigation of synthetic high-temperature plagioclases, Phys. Chem. Miner. 5 (1980) 255–277.
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066
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[22] G.Y. Lee, W.B. Im, A. Kirakosyan, S.H. Cheong, J.Y. Han, D.Y. Jeon, Tunable emission from blue to white light in single-phase Na0.34Ca(0.66 x y)Al1.66Si2.34O8:xEu2 þ ,yMn2 þ (x¼ 0.07) phosphor for white-light UV LEDs, Opt. Express 21 (2013) 3287–3297. [23] R. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr. Sect. C – Struct. Chem. 32 (1976) 751–767. [24] G.N. Nikhare, S.C. Gedam, S.J. Dhoble, Photoluminescence and thermoluminescence of Ce3 þ ions doped in LiAl5O8 and NaAl11O17 aluminate systems, J. Lumin. 137 (2013) 290–295. [25] G. Blasse, Energy transfer between inequivalent Eu2 þ ions, J. Solid State Chem. 62 (1986) 207–211. [26] R. Reisfeld, E. Greenberg, R. Velapoldi, B. Barnett, Luminescence quantum efficiency of Gd and Tb in borate glasses and the mechanism of energy transfer between them, J. Chem. Phys. 56 (1972) 1698. [27] B.M. Antipeuko, I.M. Bataev, V.L. Ermolaev, T.A. Privalova, Ion-to-ion radiationless transfer of electron excitation energy between rare-earth ions in POCl3–SnCl4, Opt. Spektrosk. 29 (1970) 335. [28] D.L. Dexter, A theory of sensitized luminescence in solids, J. Chem. Phys. 21 (1953) 836–851.
[29] L. Ozawa, P.M. Jaffe, The mechanism of the emission color shift with activator concentration in Eu þ 3 activated phosphors, J. Electrochem. Soc. 118 (1971) 1678–1679. [30] L. Van Uitert, Characterization of energy transfer interactions between rare earth ions, J. Electrochem. Soc. 114 (1976) 1048–1053. [31] M. Weng, R. Yang, Y. Peng, J. Chen, Yellowish green-emitting KSrPO4: Tb3 þ phosphors with various doping concentrations prepared by using microwave assisted sintering, Ceram. Int. 38 (2012) 1319–1323. [32] G. Zhu, Y. Wang, Z. Ci, B. Liu, Y. Shi, S. Xin, Ca8Mg(SiO4)4Cl2:Ce3 þ , Tb3 þ : a potential single-phased phosphor for white-light-emitting diodes, J. Lumin. 132 (2012) 531–536. [33] J.C. Bourcet, F.K. Fong, Quantum efficiency of diffusion limited energy transfer in La1 x yCexTbyPO4, J. Chem. Phys. 60 (1974) 34. [34] D. Dexter, J.H. Schulman, Theory of concentration quenching in inorganic phosphors, J. Chem. Phys. 22 (1954) 1063. [35] R. Reisfeld, N. Lieblich-Soffer, Energy transfer from UO2 2 þ to Sm3 þ in phosphate glass, J. Solid State Chem. 28 (1979) 391–395.
Please cite this article as: J. Dong, et al., Luminescence properties of Ce3 þ -doped and Ce3 þ –Tb3 þ co-doped Na0.34Ca0.66Al1.66Si2.34O8 phosphor for UV-LED, Ceramics International (2014), http://dx.doi.org/10.1016/j.ceramint.2014.09.066