- Email: [email protected]
Enhanced photoluminescence of CaTiO3:Sm3+ red phosphors by Na+, H3BO3 added
Materials Chemistry and Physics xxx (2016) 1e5
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added Renping Cao a, *, Guo Chen a, Xiaoguang Yu a, Pengjie Tang a, Zhiyang Luo b, Siling Guo a, Guotai Zheng a a b
College of Mathematics and Physics, Jinggangshan University, Ji'an 343009, China College of Mechanical Manufacture and Automation, Jinggangshan University, Ji'an 343009, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
CaTiO3:Sm3þ,Naþ,B3þ phosphor is synthesized by solidestate reaction method in air. Two very strong excitation bands within the range 400e435 nm and 455e510 nm are observed. The PL intensity of CaTiO3:Sm3þ phosphor increases 5e7 times by codoping Naþ and B3þions. The results are helpful to improve luminescence properties of other Sm3þ-doped phosphors.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 March 2015 Received in revised form 22 December 2015 Accepted 3 January 2016 Available online xxx
Ca[13x/2]TiO3:xSm3þ (0 x 5 mol%), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by high temperature solidestate reaction method in air. All samples are pure phase CaTiO3. Two strong excitation bands within the range 400e435 nm and 455e510 nm are observed, which are nicely match with widely applied near-UV (400e430 nm) and blue (460e500 nm) LED chips. The strongest emission band peaking at ~603 nm is assigned to the 4G5/2 / 6H7/2 transition of Sm3þ ion. The optimal Sm3þ doping concentration is ~3 mol%. Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ phosphor with excitation 408, 467, and 481 nm are ~0.809 m, 0.792 m, and 0.8 m, respectively. The PL intensity of Ca0.955TiO3:0.03Sm3þ phosphor is enhanced 5e7 times after Naþ ion is codoped as charge compensator and H3BO3 is added as flux, and their CIE chromaticity coordinate is ~ (0.5792, 0.4199). The experiment results are helpful to improve luminescence properties of other Sm3þdoped phosphors and study novel phosphors. © 2016 Elsevier B.V. All rights reserved.
Keywords: Optical materials Optical properties Luminescence Photoluminescence spectroscopy
1. Introduction The energy levels of the lanthanide ions in some crystals have been investigated and reported [1]. Rare-earth ions doped
* Corresponding author. E-mail address: [email protected] (R. Cao).
luminescence materials have been extensively researched owing to their wide applications in many fields, such as plasma display panels, field emission displays, light-emitting diodes (LEDs), cathode ray tubes, and optoelectronic devices [2e4]. The rare-earth ions are characterized by a partially filled 4f shell shielded by 5s2 and 5p6 orbitals, so, their emission bands usually show sharp lines in the optical spectra [5]. The rare-earth ions-doped phosphors, which show narrow emission owing to the “line-type” fef transition,
http://dx.doi.org/10.1016/j.matchemphys.2016.01.009 0254-0584/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
2
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
result in both a high lumen equivalent and high efficiency [6,7]. Except the property of rare-earth ions, the host doped is also one of important influencing factors to luminescent efficiency of phosphor. Layered perovskite compounds may contain larger rare-earth ion doping concentration owing to the longer distance between layers, so, layered perovskite compounds are good host materials for phosphors [8]. CaTiO3 is one of the few minerals of the perovskite-type found in nature [9]. Rare-earth ions-doped CaTiO3 phosphors have also been studied extensively due to the wellknown chemical stability which can be used as LEDs [10,11]. MTiO3:Pr3þ (M ¼ Ca, Sr, and Ba) phosphors emit intense red-light at ~ 610 nm with excitation ultraviolet (UV) light [12]. In CaTiO3:Eu3þ phosphor, the optimized excitation wavelength is ~400 nm, which is suitable for near UV LED chip, and emitted reddish orange light at ~610 nm [13]. However, their emission intensities are not so high that more-efficient red phosphors, which can be achieve an acceptable efficiency for white LEDs based on near UV or blue light LED chip. Therefore, their luminescence properties must be further improved by co-doped other ions in order to gain their practical application. Usually, Energy transfer (ET) and charge compensation are two good methods to improve the luminescence properties of phosphors. In CaTiO3: Sm3þ phosphor, Sm3þ ions are expected to replace Ca2þ ions. In order to keep charge balance in the host lattice the extra positive charge from the Sm3þ can be compensated by Ca2þ vacancies in oxidizing conditions and/or Ti4þ reduction to Ti3þ ions in reducing conditions [7,14]. Therefore, Sm3þ ions may not be fully introduced into Ca2þ sites. It would lead to the decrease of emission intensity. In order to solve this problem, alkali metal ions (e.g., Liþ, Naþ, and Kþ) are always chosen as charge compensators for phosphors due to their small ionic radii, which are easy to enter into lattice, and they are all of þ1 valence, which is convenient for charge compensation [15]. In addition, it can also be compensated by negative charge defect when Ti4þ ions are substituted by B3þ and Al3þ etc ions, consequently leading to the reinforcement of optical performances [16]. In the paper, Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol %), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by a conventional solidestate reaction method in air. Their crystal structure, fluorescence lifetimes, and luminescence properties are investigated, respectively. The relation between emission intensity and Sm3þ doping concentration is discussed, and the luminous mechanism is explained by using the schematic energy level. The influence of Naþ ions and H3BO3 to emission intensity of CaTiO3:Sm3þ phosphor is investigated, respectively. The fluorescence lifetimes are calculated. The experiment results indicate that the paper content are helpful to improve luminescence properties of other Sm3þ-doped phosphors and study novel phosphors.
sintered at 500 C for 5 h and subsequently 1200 C for 6 h in air. Repeated grindings are performed between two sintering processes to improve the homogeneity. All products are obtained after natural cooling to room temperature. Sintered specimens are sieved to classify the powder size within the range 200e400 nm by using a sieve for fluorescence and chromaticity measurements. The crystal structures of phosphors are checked by X-Ray powder diffraction (XRD) (Philips Model PW1830) with Cu-Ka radiation at 40 kV and 40 mA at room temperature. The data are collected in the 2q range from 10 to 90 . Luminescence properties and fluorescence lifetimes are investigated by using a steady-state FLS920 spectrofluorimeter (Edinburgh Instruments, UK, Edinburgh) with a high spectral resolution (signal to noise ratio > 6000:1) at room temperature. A 450 W ozone free xenon lamp is used for steady-state measurements. A microsecond pulsed xenon flash lamp mF900 with an average power of 60 W is available to record the emission decay curves for lifetimes.
3. Results and discussion The unit cell of CaTiO3 drawn on the basis of the Inorganic Crystal Structure Database (ICSD) #51024, are shown in Fig. 1. According to ICSD #51024, CaTiO3 is described in the orthorhombic crystal system with space-group Pbnm (no. 62), and the lattice parameters a ¼ 5.3814(1) Å, b ¼ 5.4418(1) Å, c ¼ 7.6409(2) Å, V ¼ 223.76 Å3, and z ¼ 4 [17]. The perovskite CaTiO3 structure is based on a network of corner-linked octahedron [TiO6] with the larger Ca cations in the central cavities. The coordination number of the Ca atom is eight oxygen atoms (2 O1þ 6 O2), and the Ca polyhedron is a four-fold antiprism structure [18]. The Sm3þ and Naþ ions occupy the Ca2þ ions site in the host lattice owing to their similar ionic radii (Sm3þ: ~0.964 Å, Naþ: ~0.95 Å, and Ca2þ: ~0.99 Å) [19]. XRD patterns of Joint Committee On Powder Diffraction Standards (JCPDS) card no. 89-6949, blank CaTiO3, Ca0.985Sm0.01TiO3, Ca0.955Sm0.03TiO3, Ca0.925Sm0.05TiO3, Ca0.955Sm0.03TiO3 þ 10 mol% H3BO3, and Ca0.94Na0.03Sm0.03TiO3 phosphors sintered at 1200 C for 6 h are shown in Fig. 2. The XRD patterns of these samples match well with the standard data of JCPDS card no. 89-6949. The XRD patterns of other Ca[13x/2]TiO3:xSm3þ (0 x 5 mol%) phosphors are not displayed in Fig. 2, but those patterns are also in line with those of JCPDS card no. 89-6949. No other crystalline phases are formed Doping of Sm3þ, Naþ ions, and H3BO3 do not cause any significant structure changes owing to their similar ionic radii (Ca2þ: ~0.99 Å, Sm3þ: ~0.964 Å, and Naþ: ~0.95 Å) and a small
2. Experiments All the chemicals are purchased from the Aladdin Chemical Reagent Company in Shanghai China, such as CaCO3 (A.R. 99.5%), Na2CO3 (A.R. 99.5%), H3BO3 (A.R. 99.5%), TiO2 (99.9%), and Sm2O3 (99.99%). Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol%), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by a conventional high temperature solidestate reaction method in air. 10 mol% H3BO3, which is defined against 1 mol of a phosphor formula, is added as flux since it is effective in stimulating the host lattice formation. Naþ ion is codoped in the same molar weight as Sm3þ ion to act as charge compensator. The stoichiometric amount of raw materials are well grounded in an agate mortar without further purification, then
Fig. 1. (a) The unit cell of CaTiO3 drawn on the basis of ICSD #51024, (b) TiO6 octahedron, (c) CaO6 polyhedron.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
Fig. 2. XRD patterns of JCPDS card no. 89e6949, blank CaTiO3, Ca0.985Sm0.01TiO3, Ca0.955Sm0.03TiO3, Ca0.925Sm0.05TiO3, Ca0.955Sm0.03TiO3 þ 10 mol% H3BO3, and Ca0.94Na0.03Sm0.03TiO3 phosphors sintered at 1200 C for 6 h.
amount of dopant. This is said that all samples are pure phase CaTiO3. Photoluminescence (PL) and Photoluminescence excitation (PLE) spectra of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature (lex ¼ 408, 467, and 481 nm; lem ¼ 603 nm) are shown in Fig. 3. The PLE spectrum of Ca0.955TiO3:0.03Sm3þ phosphor with monitoring 603 nm is composed of a series of PLE bands peaking at ~320, 350, 360, 380, 408, 425, 440, 467, 481, and 530 nm in the range of 200e550 nm. The broad PLE band peaking at ~320 nm within the range 250e340 nm is ascribed to the O2eSm3þ and O2eTi4þ charge transfer bands (CTB), other PLE bands are attributed to 6H5/2 / (4H9/2, 4F9/2, 6P7/2, 4F7/2, 6P5/2, 4G9/2, 4I13/2, 4I11/2, and 4 F3/2) transitions of Sm3þ ion, respectively [20,21]. There is a very significant phenomenon that two very strong excitation bands within the range 400e435 nm and 455e510 nm are observed at the same time, which is different from those reported [17,22]. It is said that PL intensity of Sm3þ ion is affected by crystal field of the host. These PLE bands indicate that CaTiO3:Sm3þ phosphor can be well excited by near UV (400e430 nm) and blue (460e500 nm) light and nicely match with widely applied near-UV and blue LED chips. The PL spectra of Ca0.955TiO3:0.03Sm3þ phosphor with different excitation wavelengths (e.g., 408 nm, 467 nm, and 481 nm) cover the region from 530 to 750 nm, and their PL spectrum shapes and intensities are almost the same. This is said that there is only Sm3þ ion luminescence center. Four PL bands within the range 530e750 nm including 550e580, 580e630, 630e690, and 690e750 nm can be observed, which may be assigned to the 4G5/2 / 6HJ (J ¼ 5/2, 7/2, 9/2, and 11/2) transitions of Sm3þ ion, respectively [23,24]. The schematic energy levels of [TiO6] group and Sm3þ ion, and
Fig. 3. PL and PLE spectra of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature (lex ¼ 408, 467, and 481 nm; lem ¼ 603 nm).
3
ET process from TiO2 group to Sm3þ ion in the CaTiO3:Sm3þ 3 phosphor are depicted in Fig. 4. After absorbing energy, electrons are pumped into the charge transfer (CT) state of the TiO2 3 group from valence band, then, the excitation energy is transferred directly from the TiO2 3 group to the high level excited states of Sm3þ ion by ET process. Sm3þ ion with 4f5 configuration has complicated energy levels and various possible transitions between f levels. In the CaTiO3:Sm3þ phosphor, the electrons in Sm3þ ion absorb energy and are raised from the ground state 6H5/2 to the high level excited states. So, all the peaks of the excitation spectra are due to the excitation from ground-level 6H5/2 to higher energy levels of Sm3þ ion. The excited electrons then relax to the lower level by a nonradiative process, and finally populate the lowest excited state 4G5/2 level. When the 4G5/2 level is populated, the possible electron transitions by cross relaxation processes from 4G5/ 6 2 to HJ (J ¼ 5/2, 7/2, 9/2, and 11/2) may occur, thus, the phosphors emit reddish orange light [25]. PL spectra of Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol %) phosphors at room temperature (lex ¼ 467 nm) and the relation between PL intensity and Sm3þ doping concentration are shown in Fig. 5. The PL spectrum of CaTiO3 host with excitation 467 nm is not observed in the range of 550e750 nm. This means that the emission comes from the Sm3þ ion. All PL spectra of Ca[13x/ 3þ (x ¼ 0.5, 1, 2, 3, 4, and 5 mol%) phosphors show the 2]TiO3:xSm same peak shape except the PL intensity with changing Sm3þ doping concentration within the range 0.5e5 mol%. PL intensity increases with increasing Sm3þ doping concentration in the range of 0.5e3 mol%, then decreases with further increasing Sm3þ doping concentration. The former observation can be attributed to the distance between Sm3þ ions. The nonradiative energy transfer between Sm3þ ions occur easily due to decreasing the distance between the Sm3þ ions luminescent centers after the concentration of Sm3þ ions increases. The latter observation is due to the concentration quenching of Sm3þ ions. Therefore, the optimal Sm3þ doping concentration is ~3 mol%. Decay curves of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature and the relation between fluorescent lifetime and Sm3þ doping concentration in the range of 0.5e5 mol% are shown in Fig. 6. The monitoring wavelength is 603 nm with excitation 408, 467, and 481 nm, respectively. These red curves are a fit of the experimental data to a first order exponential decay equation. Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ phosphor with
Fig. 4. Energy level diagrams of [TiO6] group and Sm3þ ion and ET process from TiO2 3 group to Sm3þ ion in the CaTiO3:Sm3þ phosphor.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
4
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
Fig. 5. PL spectra of Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol%) phosphors at room temperature (lex ¼ 467 nm). The inset: The relation between PL intensity and Sm3þ doping concentration.
Fig. 6. Decay curves of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature. The monitoring wavelength is 603 nm with excitation 408, 467, and 481 nm, respectively. The inset: The relation between fluorescent lifetime and Sm3þ doping concentration in the range of 0.5e5 mol% (lex ¼ 467 nm, lem ¼ 603 nm). These red curves are a fit of the experimental data to a first order exponential decay equation (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
excitation 408 nm, 467 nm, and 481 nm are ~0.809, 0.792, and 0.8 m, respectively. The fluorescent lifetimes of Ca[13x/ 3þ (x ¼ 0.5, 1, 2, 3, 4, and 5 mol%) phosphors 2]TiO3:xSm (lex ¼ 467 nm, lem ¼ 603 nm) decrease from 0.84 to 0.77 m with increasing Sm3þ doping concentration within the range 0.5e5 mol %. The luminescence decay curve can be well fitted by a first-order exponential function [1].
t IðtÞ ¼ Ið0Þ exp t
Fig. 7. PL spectra of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature (lex ¼ 467 nm). The inset: The CIE chromaticity diagram and chromaticity coordinates.
ion cannot be fully introduced into the Ca2þ ion site in order to keep charge balance. Usually, alkali metal ions (e.g., Liþ, Naþ, and Kþ) are chosen as charge compensator for phosphors due to its small ionic radius, easy to enter into the lattice, and convenient for charge compensation [1]. Here, Naþ ion is chosen as charge compensator. In host CaTiO3, Ca/O bond is almost the same as Na/O bond because their ionic radii are the similar (Ca2þ: 0.99 Å and Naþ: 0.95 Å), thus, the lattice distortion is small after Naþ ions replace Ca2þ ions in the host. According to the PL spectra in Fig. 7, with excitation 467 nm, the PL intensity of Ca0.955TiO3:0.03Sm3þ phosphor is increased 5e7 times after Naþ ion is codoped as charge compensator and H3BO3 is added as flux, and their CIE chromaticity coordinate is about (0.5792, 0.4199). According to the theory of charge compensation, the extra positive charge defect from Sm3þ can be compensated effectively in the CaTiO3 lattice when Ca2þ ion is replaced by Naþ ion and Ti4þ ion is substituted by B3þ ion, consequently leading to the enhancement of luminescence properties. Decay curves of Ca0.955TiO3:0.03Sm3þ, 3þ Ca0.955TiO3:0.03Sm þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature are shown in Fig. 8. The monitoring wavelength is 603 nm with excitation 467 nm. These red curves are a fit of the experimental data to a first order exponential decay equation (see formula 1). Their decay curves comply well with single exponential decay equation, fitting
(1)
where, I(t) is the luminescence intensity at time t, I(0) is the initial luminescence intensity, t is the time, and t is the decay time for the exponential components. PL spectra of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature (lex ¼ 467 nm) and the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates are shown in Fig. 7. It is well known that Sm3þ ions are expected to replace Ca2þ ions in the CaTiO3 host lattice, and it is difficult to keep charge balance in the lattice due to their different valence state. An extra positive charge in the lattice generates and has to be compensated by the defect site generated by the incorporation of second dopant at the Ti4þ site [7]. Thus, Sm3þ
Fig. 8. Decay curves of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature. The monitoring wavelength is 603 nm with excitation 467 nm. These red curves are a fit of the experimental data to a first order exponential decay equation (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
to which produces a lifetime of ~0.792 m, 0.587 ms, and 0.781 ms, respectively. 4. Conclusions In summary, Ca[13x/2]TiO3:xSm3þ (0 x 5 mol%), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by high temperature solidestate reaction method in air. Their crystal structures, fluorescence lifetimes, and luminescence properties are investigated, respectively. All samples are pure phase CaTiO3. A series of PLE bands peaking at ~320, 350, 360, 380, 408, 425, 440, 467, 481, and 530 nm in the range of 200e550 nm are observed due to the O2eSm3þ CT, O2eTi4þ CTB, 6H5/2 / (4H9/2, 4F9/2, 6P7/2, 4F7/2, 6P5/2, 4G9/2, 4I13/2, 4 I11/2, and 4F3/2) transitions of Sm3þ ion, respectively. Four PL bands within the range 530e750 nm including 550e580, 580e630, 630e690, and 690e750 nm can be observed owing to the 4G5/2 / 6 HJ (J ¼ 5/2, 7/2, 9/2, and 11/2) transitions of Sm3þ ion, respectively. The optimal Sm3þ doping concentration in CaTiO3:Sm3þ phosphor is ~3 mol%. Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ phosphor with excitation 408, 467, and 481 nm are ~0.809 m, 0.792 m, and 0.8 m, respectively. The PL intensity of Ca0.955TiO3:0.03Sm3þ phosphor may be enhanced 5e7 times after Naþ ion is codoped as charge compensator and H3BO3 is added as flux, and the CIE chromaticity coordinate is about (0.5792, 0.4199). Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors are ~0.792 m, 0.587 ms, and 0.781 ms with excitation 467 nm, respectively. The experiment results indicate that the thesis contents are useful to improve luminescence properties of other Sm3þ-doped phosphors. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (Grant nos. 11464021), Natural Science Foundation of Jiangxi Province of China (no. 20151BAB202008).
5
References [1] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer-Verlag, BerlinHeidelberg, 1994. [2] R. Cao, G. Chen, X. Yu, C. Cao, K. Chen, P. Liu, S. Jiang, J. Solid State Chem. 220 (2014) 97e101. [3] Y. Chen, J. Wang, C.M. Liu, X.J. Kuang, Q. Su, Appl. Phys. Lett. 98 (2011) 081917 (3 pages). [4] N.M. Zhang, C.F. Guo, H. Jing, J.H. Jeong, Spectrochim. Acta, Part A 116 (2013) 556e561. [5] G. Blasse, A. Bril, Phys. Lett. 23 (7) (1966) 440e441. [6] R.P. Cao, C.C. Cao, X.G. Yu, W.S. Li, J.R. Qiu, Int. J. Appl. Ceram. Technol. 1e5 (2015). [7] H. Ryu, B.K. Singh, K.S. Bartwal, M.G. Brik, I.V. Kity, Acta Mater 56 (2008) 358e363. [8] H.F. Kay, P.C. Bailey, Acta Cryst. 10 (1957) 219e226. [9] X. Liu, R.C. Liebermann, Phys. Chem. Min. 20 (1993) 171e175. [10] M.G. Ha, J.H. Lee, J.S. Bae, J.P. Kim, E.D. Jeong, K.S. Hong, H.S. Yang, Curr. Appl. Phys. 11 (2011) 1379e1383. [11] S. Okamoto, H. Yamamoto, J. Lumin 102/103 (2003) 586e589. [12] R. Fujiwara, H. Sano, M. Shimizu, M. Kuwabara, J. Lumin 129 (2009) 231e237. [13] J. Fu, Q. Zhang, Y. Li, H. Wang, J. Lumin 130 (2010) 231e235. [14] J.A. Dawson, X. Li, C.L. Freeman, J.H. Harding, D.C. Sinclair, J. Mater. Chem. C 1 (2013) 1574e1582. [15] L.S. Zhao, J. Liu, Z.C. Wu, S.P. Kuang, Spectrochim. Acta, Part A 87 (2012) 228e231. [16] P.P. Liu, J. Yin, X.Y. Mi, L.X. Zhang, L.J. Bie, J. Rare Earths 31 (6) (2013) 555e558. [17] A.R. Chakhmouradian, R.H. Mitchell, J. Solid State Chem. 138 (1998) 272e277. [18] S. Sasaki, C.T. Prewrrr, J.D. Bass, Acta Cryst. C43 (1987) 1668e1674. [19] R.D. Shannon, Acta Cryst. A 32 (1976) 751e767. [20] G.H. Dieke, Spectra and Energy Levels of Rare Earth Ions in Crystals, Interscience, New York, 1968. [21] M. Shivaram, H. Nagabhushana, S.C. Sharma, S.C. Prashantha, B. Daruka Prasad, N. Dhananjaya, R. Hari Krishna, B.M. Nagabhushana, C. Shivakumara, R.P.S. Chakradhar, Spectrochim. Acta Part A 128 (2014) 891e901. [22] S. Sakirzanovas, A. Katelnikovas, H. Bettentrup, A. Kareiva, T. Jüstel, J. Lumin 131 (2011) 1525e1529. [23] F. Yang, Y.F. Liu, X.D. Tian, G.Y. Dong, Q.M. Yu, J. Solid State Chem. 225 (2015) 19e23. [24] R. Cao, H. Xu, D. Peng, Q. Gou, S. Zhou, P. Liu, X. Yu, J. Mater. Sci. Mater. Electron. 26 (2015) 6776e6780. [25] Z.H. Ju, R.P. Wei, J.X. Ma, C.R. Pang, W.S. Liu, J. Alloys Compd. 507 (2010) 133e136.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added Renping Cao a, *, Guo Chen a, Xiaoguang Yu a, Pengjie Tang a, Zhiyang Luo b, Siling Guo a, Guotai Zheng a a b
College of Mathematics and Physics, Jinggangshan University, Ji'an 343009, China College of Mechanical Manufacture and Automation, Jinggangshan University, Ji'an 343009, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
CaTiO3:Sm3þ,Naþ,B3þ phosphor is synthesized by solidestate reaction method in air. Two very strong excitation bands within the range 400e435 nm and 455e510 nm are observed. The PL intensity of CaTiO3:Sm3þ phosphor increases 5e7 times by codoping Naþ and B3þions. The results are helpful to improve luminescence properties of other Sm3þ-doped phosphors.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 March 2015 Received in revised form 22 December 2015 Accepted 3 January 2016 Available online xxx
Ca[13x/2]TiO3:xSm3þ (0 x 5 mol%), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by high temperature solidestate reaction method in air. All samples are pure phase CaTiO3. Two strong excitation bands within the range 400e435 nm and 455e510 nm are observed, which are nicely match with widely applied near-UV (400e430 nm) and blue (460e500 nm) LED chips. The strongest emission band peaking at ~603 nm is assigned to the 4G5/2 / 6H7/2 transition of Sm3þ ion. The optimal Sm3þ doping concentration is ~3 mol%. Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ phosphor with excitation 408, 467, and 481 nm are ~0.809 m, 0.792 m, and 0.8 m, respectively. The PL intensity of Ca0.955TiO3:0.03Sm3þ phosphor is enhanced 5e7 times after Naþ ion is codoped as charge compensator and H3BO3 is added as flux, and their CIE chromaticity coordinate is ~ (0.5792, 0.4199). The experiment results are helpful to improve luminescence properties of other Sm3þdoped phosphors and study novel phosphors. © 2016 Elsevier B.V. All rights reserved.
Keywords: Optical materials Optical properties Luminescence Photoluminescence spectroscopy
1. Introduction The energy levels of the lanthanide ions in some crystals have been investigated and reported [1]. Rare-earth ions doped
* Corresponding author. E-mail address: [email protected] (R. Cao).
luminescence materials have been extensively researched owing to their wide applications in many fields, such as plasma display panels, field emission displays, light-emitting diodes (LEDs), cathode ray tubes, and optoelectronic devices [2e4]. The rare-earth ions are characterized by a partially filled 4f shell shielded by 5s2 and 5p6 orbitals, so, their emission bands usually show sharp lines in the optical spectra [5]. The rare-earth ions-doped phosphors, which show narrow emission owing to the “line-type” fef transition,
http://dx.doi.org/10.1016/j.matchemphys.2016.01.009 0254-0584/© 2016 Elsevier B.V. All rights reserved.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
2
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
result in both a high lumen equivalent and high efficiency [6,7]. Except the property of rare-earth ions, the host doped is also one of important influencing factors to luminescent efficiency of phosphor. Layered perovskite compounds may contain larger rare-earth ion doping concentration owing to the longer distance between layers, so, layered perovskite compounds are good host materials for phosphors [8]. CaTiO3 is one of the few minerals of the perovskite-type found in nature [9]. Rare-earth ions-doped CaTiO3 phosphors have also been studied extensively due to the wellknown chemical stability which can be used as LEDs [10,11]. MTiO3:Pr3þ (M ¼ Ca, Sr, and Ba) phosphors emit intense red-light at ~ 610 nm with excitation ultraviolet (UV) light [12]. In CaTiO3:Eu3þ phosphor, the optimized excitation wavelength is ~400 nm, which is suitable for near UV LED chip, and emitted reddish orange light at ~610 nm [13]. However, their emission intensities are not so high that more-efficient red phosphors, which can be achieve an acceptable efficiency for white LEDs based on near UV or blue light LED chip. Therefore, their luminescence properties must be further improved by co-doped other ions in order to gain their practical application. Usually, Energy transfer (ET) and charge compensation are two good methods to improve the luminescence properties of phosphors. In CaTiO3: Sm3þ phosphor, Sm3þ ions are expected to replace Ca2þ ions. In order to keep charge balance in the host lattice the extra positive charge from the Sm3þ can be compensated by Ca2þ vacancies in oxidizing conditions and/or Ti4þ reduction to Ti3þ ions in reducing conditions [7,14]. Therefore, Sm3þ ions may not be fully introduced into Ca2þ sites. It would lead to the decrease of emission intensity. In order to solve this problem, alkali metal ions (e.g., Liþ, Naþ, and Kþ) are always chosen as charge compensators for phosphors due to their small ionic radii, which are easy to enter into lattice, and they are all of þ1 valence, which is convenient for charge compensation [15]. In addition, it can also be compensated by negative charge defect when Ti4þ ions are substituted by B3þ and Al3þ etc ions, consequently leading to the reinforcement of optical performances [16]. In the paper, Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol %), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by a conventional solidestate reaction method in air. Their crystal structure, fluorescence lifetimes, and luminescence properties are investigated, respectively. The relation between emission intensity and Sm3þ doping concentration is discussed, and the luminous mechanism is explained by using the schematic energy level. The influence of Naþ ions and H3BO3 to emission intensity of CaTiO3:Sm3þ phosphor is investigated, respectively. The fluorescence lifetimes are calculated. The experiment results indicate that the paper content are helpful to improve luminescence properties of other Sm3þ-doped phosphors and study novel phosphors.
sintered at 500 C for 5 h and subsequently 1200 C for 6 h in air. Repeated grindings are performed between two sintering processes to improve the homogeneity. All products are obtained after natural cooling to room temperature. Sintered specimens are sieved to classify the powder size within the range 200e400 nm by using a sieve for fluorescence and chromaticity measurements. The crystal structures of phosphors are checked by X-Ray powder diffraction (XRD) (Philips Model PW1830) with Cu-Ka radiation at 40 kV and 40 mA at room temperature. The data are collected in the 2q range from 10 to 90 . Luminescence properties and fluorescence lifetimes are investigated by using a steady-state FLS920 spectrofluorimeter (Edinburgh Instruments, UK, Edinburgh) with a high spectral resolution (signal to noise ratio > 6000:1) at room temperature. A 450 W ozone free xenon lamp is used for steady-state measurements. A microsecond pulsed xenon flash lamp mF900 with an average power of 60 W is available to record the emission decay curves for lifetimes.
3. Results and discussion The unit cell of CaTiO3 drawn on the basis of the Inorganic Crystal Structure Database (ICSD) #51024, are shown in Fig. 1. According to ICSD #51024, CaTiO3 is described in the orthorhombic crystal system with space-group Pbnm (no. 62), and the lattice parameters a ¼ 5.3814(1) Å, b ¼ 5.4418(1) Å, c ¼ 7.6409(2) Å, V ¼ 223.76 Å3, and z ¼ 4 [17]. The perovskite CaTiO3 structure is based on a network of corner-linked octahedron [TiO6] with the larger Ca cations in the central cavities. The coordination number of the Ca atom is eight oxygen atoms (2 O1þ 6 O2), and the Ca polyhedron is a four-fold antiprism structure [18]. The Sm3þ and Naþ ions occupy the Ca2þ ions site in the host lattice owing to their similar ionic radii (Sm3þ: ~0.964 Å, Naþ: ~0.95 Å, and Ca2þ: ~0.99 Å) [19]. XRD patterns of Joint Committee On Powder Diffraction Standards (JCPDS) card no. 89-6949, blank CaTiO3, Ca0.985Sm0.01TiO3, Ca0.955Sm0.03TiO3, Ca0.925Sm0.05TiO3, Ca0.955Sm0.03TiO3 þ 10 mol% H3BO3, and Ca0.94Na0.03Sm0.03TiO3 phosphors sintered at 1200 C for 6 h are shown in Fig. 2. The XRD patterns of these samples match well with the standard data of JCPDS card no. 89-6949. The XRD patterns of other Ca[13x/2]TiO3:xSm3þ (0 x 5 mol%) phosphors are not displayed in Fig. 2, but those patterns are also in line with those of JCPDS card no. 89-6949. No other crystalline phases are formed Doping of Sm3þ, Naþ ions, and H3BO3 do not cause any significant structure changes owing to their similar ionic radii (Ca2þ: ~0.99 Å, Sm3þ: ~0.964 Å, and Naþ: ~0.95 Å) and a small
2. Experiments All the chemicals are purchased from the Aladdin Chemical Reagent Company in Shanghai China, such as CaCO3 (A.R. 99.5%), Na2CO3 (A.R. 99.5%), H3BO3 (A.R. 99.5%), TiO2 (99.9%), and Sm2O3 (99.99%). Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol%), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by a conventional high temperature solidestate reaction method in air. 10 mol% H3BO3, which is defined against 1 mol of a phosphor formula, is added as flux since it is effective in stimulating the host lattice formation. Naþ ion is codoped in the same molar weight as Sm3þ ion to act as charge compensator. The stoichiometric amount of raw materials are well grounded in an agate mortar without further purification, then
Fig. 1. (a) The unit cell of CaTiO3 drawn on the basis of ICSD #51024, (b) TiO6 octahedron, (c) CaO6 polyhedron.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
Fig. 2. XRD patterns of JCPDS card no. 89e6949, blank CaTiO3, Ca0.985Sm0.01TiO3, Ca0.955Sm0.03TiO3, Ca0.925Sm0.05TiO3, Ca0.955Sm0.03TiO3 þ 10 mol% H3BO3, and Ca0.94Na0.03Sm0.03TiO3 phosphors sintered at 1200 C for 6 h.
amount of dopant. This is said that all samples are pure phase CaTiO3. Photoluminescence (PL) and Photoluminescence excitation (PLE) spectra of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature (lex ¼ 408, 467, and 481 nm; lem ¼ 603 nm) are shown in Fig. 3. The PLE spectrum of Ca0.955TiO3:0.03Sm3þ phosphor with monitoring 603 nm is composed of a series of PLE bands peaking at ~320, 350, 360, 380, 408, 425, 440, 467, 481, and 530 nm in the range of 200e550 nm. The broad PLE band peaking at ~320 nm within the range 250e340 nm is ascribed to the O2eSm3þ and O2eTi4þ charge transfer bands (CTB), other PLE bands are attributed to 6H5/2 / (4H9/2, 4F9/2, 6P7/2, 4F7/2, 6P5/2, 4G9/2, 4I13/2, 4I11/2, and 4 F3/2) transitions of Sm3þ ion, respectively [20,21]. There is a very significant phenomenon that two very strong excitation bands within the range 400e435 nm and 455e510 nm are observed at the same time, which is different from those reported [17,22]. It is said that PL intensity of Sm3þ ion is affected by crystal field of the host. These PLE bands indicate that CaTiO3:Sm3þ phosphor can be well excited by near UV (400e430 nm) and blue (460e500 nm) light and nicely match with widely applied near-UV and blue LED chips. The PL spectra of Ca0.955TiO3:0.03Sm3þ phosphor with different excitation wavelengths (e.g., 408 nm, 467 nm, and 481 nm) cover the region from 530 to 750 nm, and their PL spectrum shapes and intensities are almost the same. This is said that there is only Sm3þ ion luminescence center. Four PL bands within the range 530e750 nm including 550e580, 580e630, 630e690, and 690e750 nm can be observed, which may be assigned to the 4G5/2 / 6HJ (J ¼ 5/2, 7/2, 9/2, and 11/2) transitions of Sm3þ ion, respectively [23,24]. The schematic energy levels of [TiO6] group and Sm3þ ion, and
Fig. 3. PL and PLE spectra of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature (lex ¼ 408, 467, and 481 nm; lem ¼ 603 nm).
3
ET process from TiO2 group to Sm3þ ion in the CaTiO3:Sm3þ 3 phosphor are depicted in Fig. 4. After absorbing energy, electrons are pumped into the charge transfer (CT) state of the TiO2 3 group from valence band, then, the excitation energy is transferred directly from the TiO2 3 group to the high level excited states of Sm3þ ion by ET process. Sm3þ ion with 4f5 configuration has complicated energy levels and various possible transitions between f levels. In the CaTiO3:Sm3þ phosphor, the electrons in Sm3þ ion absorb energy and are raised from the ground state 6H5/2 to the high level excited states. So, all the peaks of the excitation spectra are due to the excitation from ground-level 6H5/2 to higher energy levels of Sm3þ ion. The excited electrons then relax to the lower level by a nonradiative process, and finally populate the lowest excited state 4G5/2 level. When the 4G5/2 level is populated, the possible electron transitions by cross relaxation processes from 4G5/ 6 2 to HJ (J ¼ 5/2, 7/2, 9/2, and 11/2) may occur, thus, the phosphors emit reddish orange light [25]. PL spectra of Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol %) phosphors at room temperature (lex ¼ 467 nm) and the relation between PL intensity and Sm3þ doping concentration are shown in Fig. 5. The PL spectrum of CaTiO3 host with excitation 467 nm is not observed in the range of 550e750 nm. This means that the emission comes from the Sm3þ ion. All PL spectra of Ca[13x/ 3þ (x ¼ 0.5, 1, 2, 3, 4, and 5 mol%) phosphors show the 2]TiO3:xSm same peak shape except the PL intensity with changing Sm3þ doping concentration within the range 0.5e5 mol%. PL intensity increases with increasing Sm3þ doping concentration in the range of 0.5e3 mol%, then decreases with further increasing Sm3þ doping concentration. The former observation can be attributed to the distance between Sm3þ ions. The nonradiative energy transfer between Sm3þ ions occur easily due to decreasing the distance between the Sm3þ ions luminescent centers after the concentration of Sm3þ ions increases. The latter observation is due to the concentration quenching of Sm3þ ions. Therefore, the optimal Sm3þ doping concentration is ~3 mol%. Decay curves of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature and the relation between fluorescent lifetime and Sm3þ doping concentration in the range of 0.5e5 mol% are shown in Fig. 6. The monitoring wavelength is 603 nm with excitation 408, 467, and 481 nm, respectively. These red curves are a fit of the experimental data to a first order exponential decay equation. Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ phosphor with
Fig. 4. Energy level diagrams of [TiO6] group and Sm3þ ion and ET process from TiO2 3 group to Sm3þ ion in the CaTiO3:Sm3þ phosphor.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
4
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
Fig. 5. PL spectra of Ca[13x/2]TiO3:xSm3þ (x ¼ 0, 0.5, 1, 2, 3, 4, and 5 mol%) phosphors at room temperature (lex ¼ 467 nm). The inset: The relation between PL intensity and Sm3þ doping concentration.
Fig. 6. Decay curves of Ca0.955TiO3:0.03Sm3þ phosphor at room temperature. The monitoring wavelength is 603 nm with excitation 408, 467, and 481 nm, respectively. The inset: The relation between fluorescent lifetime and Sm3þ doping concentration in the range of 0.5e5 mol% (lex ¼ 467 nm, lem ¼ 603 nm). These red curves are a fit of the experimental data to a first order exponential decay equation (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
excitation 408 nm, 467 nm, and 481 nm are ~0.809, 0.792, and 0.8 m, respectively. The fluorescent lifetimes of Ca[13x/ 3þ (x ¼ 0.5, 1, 2, 3, 4, and 5 mol%) phosphors 2]TiO3:xSm (lex ¼ 467 nm, lem ¼ 603 nm) decrease from 0.84 to 0.77 m with increasing Sm3þ doping concentration within the range 0.5e5 mol %. The luminescence decay curve can be well fitted by a first-order exponential function [1].
t IðtÞ ¼ Ið0Þ exp t
Fig. 7. PL spectra of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature (lex ¼ 467 nm). The inset: The CIE chromaticity diagram and chromaticity coordinates.
ion cannot be fully introduced into the Ca2þ ion site in order to keep charge balance. Usually, alkali metal ions (e.g., Liþ, Naþ, and Kþ) are chosen as charge compensator for phosphors due to its small ionic radius, easy to enter into the lattice, and convenient for charge compensation [1]. Here, Naþ ion is chosen as charge compensator. In host CaTiO3, Ca/O bond is almost the same as Na/O bond because their ionic radii are the similar (Ca2þ: 0.99 Å and Naþ: 0.95 Å), thus, the lattice distortion is small after Naþ ions replace Ca2þ ions in the host. According to the PL spectra in Fig. 7, with excitation 467 nm, the PL intensity of Ca0.955TiO3:0.03Sm3þ phosphor is increased 5e7 times after Naþ ion is codoped as charge compensator and H3BO3 is added as flux, and their CIE chromaticity coordinate is about (0.5792, 0.4199). According to the theory of charge compensation, the extra positive charge defect from Sm3þ can be compensated effectively in the CaTiO3 lattice when Ca2þ ion is replaced by Naþ ion and Ti4þ ion is substituted by B3þ ion, consequently leading to the enhancement of luminescence properties. Decay curves of Ca0.955TiO3:0.03Sm3þ, 3þ Ca0.955TiO3:0.03Sm þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature are shown in Fig. 8. The monitoring wavelength is 603 nm with excitation 467 nm. These red curves are a fit of the experimental data to a first order exponential decay equation (see formula 1). Their decay curves comply well with single exponential decay equation, fitting
(1)
where, I(t) is the luminescence intensity at time t, I(0) is the initial luminescence intensity, t is the time, and t is the decay time for the exponential components. PL spectra of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature (lex ¼ 467 nm) and the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates are shown in Fig. 7. It is well known that Sm3þ ions are expected to replace Ca2þ ions in the CaTiO3 host lattice, and it is difficult to keep charge balance in the lattice due to their different valence state. An extra positive charge in the lattice generates and has to be compensated by the defect site generated by the incorporation of second dopant at the Ti4þ site [7]. Thus, Sm3þ
Fig. 8. Decay curves of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors at room temperature. The monitoring wavelength is 603 nm with excitation 467 nm. These red curves are a fit of the experimental data to a first order exponential decay equation (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009
R. Cao et al. / Materials Chemistry and Physics xxx (2016) 1e5
to which produces a lifetime of ~0.792 m, 0.587 ms, and 0.781 ms, respectively. 4. Conclusions In summary, Ca[13x/2]TiO3:xSm3þ (0 x 5 mol%), Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, Ca0.94TiO3:0.03Sm3þ, 0.03Naþ phosphors are synthesized by high temperature solidestate reaction method in air. Their crystal structures, fluorescence lifetimes, and luminescence properties are investigated, respectively. All samples are pure phase CaTiO3. A series of PLE bands peaking at ~320, 350, 360, 380, 408, 425, 440, 467, 481, and 530 nm in the range of 200e550 nm are observed due to the O2eSm3þ CT, O2eTi4þ CTB, 6H5/2 / (4H9/2, 4F9/2, 6P7/2, 4F7/2, 6P5/2, 4G9/2, 4I13/2, 4 I11/2, and 4F3/2) transitions of Sm3þ ion, respectively. Four PL bands within the range 530e750 nm including 550e580, 580e630, 630e690, and 690e750 nm can be observed owing to the 4G5/2 / 6 HJ (J ¼ 5/2, 7/2, 9/2, and 11/2) transitions of Sm3þ ion, respectively. The optimal Sm3þ doping concentration in CaTiO3:Sm3þ phosphor is ~3 mol%. Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ phosphor with excitation 408, 467, and 481 nm are ~0.809 m, 0.792 m, and 0.8 m, respectively. The PL intensity of Ca0.955TiO3:0.03Sm3þ phosphor may be enhanced 5e7 times after Naþ ion is codoped as charge compensator and H3BO3 is added as flux, and the CIE chromaticity coordinate is about (0.5792, 0.4199). Fluorescent lifetimes of Ca0.955TiO3:0.03Sm3þ, Ca0.955TiO3:0.03Sm3þ þ 10 mol% H3BO3, and Ca0.94Na0.03TiO3:0.03Sm3þ phosphors are ~0.792 m, 0.587 ms, and 0.781 ms with excitation 467 nm, respectively. The experiment results indicate that the thesis contents are useful to improve luminescence properties of other Sm3þ-doped phosphors. Acknowledgments This work was financially supported by the National Natural Science Foundation of China (Grant nos. 11464021), Natural Science Foundation of Jiangxi Province of China (no. 20151BAB202008).
5
References [1] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer-Verlag, BerlinHeidelberg, 1994. [2] R. Cao, G. Chen, X. Yu, C. Cao, K. Chen, P. Liu, S. Jiang, J. Solid State Chem. 220 (2014) 97e101. [3] Y. Chen, J. Wang, C.M. Liu, X.J. Kuang, Q. Su, Appl. Phys. Lett. 98 (2011) 081917 (3 pages). [4] N.M. Zhang, C.F. Guo, H. Jing, J.H. Jeong, Spectrochim. Acta, Part A 116 (2013) 556e561. [5] G. Blasse, A. Bril, Phys. Lett. 23 (7) (1966) 440e441. [6] R.P. Cao, C.C. Cao, X.G. Yu, W.S. Li, J.R. Qiu, Int. J. Appl. Ceram. Technol. 1e5 (2015). [7] H. Ryu, B.K. Singh, K.S. Bartwal, M.G. Brik, I.V. Kity, Acta Mater 56 (2008) 358e363. [8] H.F. Kay, P.C. Bailey, Acta Cryst. 10 (1957) 219e226. [9] X. Liu, R.C. Liebermann, Phys. Chem. Min. 20 (1993) 171e175. [10] M.G. Ha, J.H. Lee, J.S. Bae, J.P. Kim, E.D. Jeong, K.S. Hong, H.S. Yang, Curr. Appl. Phys. 11 (2011) 1379e1383. [11] S. Okamoto, H. Yamamoto, J. Lumin 102/103 (2003) 586e589. [12] R. Fujiwara, H. Sano, M. Shimizu, M. Kuwabara, J. Lumin 129 (2009) 231e237. [13] J. Fu, Q. Zhang, Y. Li, H. Wang, J. Lumin 130 (2010) 231e235. [14] J.A. Dawson, X. Li, C.L. Freeman, J.H. Harding, D.C. Sinclair, J. Mater. Chem. C 1 (2013) 1574e1582. [15] L.S. Zhao, J. Liu, Z.C. Wu, S.P. Kuang, Spectrochim. Acta, Part A 87 (2012) 228e231. [16] P.P. Liu, J. Yin, X.Y. Mi, L.X. Zhang, L.J. Bie, J. Rare Earths 31 (6) (2013) 555e558. [17] A.R. Chakhmouradian, R.H. Mitchell, J. Solid State Chem. 138 (1998) 272e277. [18] S. Sasaki, C.T. Prewrrr, J.D. Bass, Acta Cryst. C43 (1987) 1668e1674. [19] R.D. Shannon, Acta Cryst. A 32 (1976) 751e767. [20] G.H. Dieke, Spectra and Energy Levels of Rare Earth Ions in Crystals, Interscience, New York, 1968. [21] M. Shivaram, H. Nagabhushana, S.C. Sharma, S.C. Prashantha, B. Daruka Prasad, N. Dhananjaya, R. Hari Krishna, B.M. Nagabhushana, C. Shivakumara, R.P.S. Chakradhar, Spectrochim. Acta Part A 128 (2014) 891e901. [22] S. Sakirzanovas, A. Katelnikovas, H. Bettentrup, A. Kareiva, T. Jüstel, J. Lumin 131 (2011) 1525e1529. [23] F. Yang, Y.F. Liu, X.D. Tian, G.Y. Dong, Q.M. Yu, J. Solid State Chem. 225 (2015) 19e23. [24] R. Cao, H. Xu, D. Peng, Q. Gou, S. Zhou, P. Liu, X. Yu, J. Mater. Sci. Mater. Electron. 26 (2015) 6776e6780. [25] Z.H. Ju, R.P. Wei, J.X. Ma, C.R. Pang, W.S. Liu, J. Alloys Compd. 507 (2010) 133e136.
Please cite this article in press as: R. Cao, et al., Enhanced photoluminescence of CaTiO3:Sm3þ red phosphors by Naþ, H3BO3 added, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.01.009