- Email: [email protected]
Bi3+) phosphor
Accepted Manuscript 3+ 3+ 3+ 3+ Synthesis and luminescence properties of La2Zr2O7:R (R = Sm , Bi , Sm /Bi ) phosphor Renping Cao, Guanjun Quan, Zhihui Shi, Ting Chen, Zhiyang Luo, Guotai Zheng, Zuofu Hu PII:
S0022-3697(17)32441-1
DOI:
10.1016/j.jpcs.2018.03.002
Reference:
PCS 8472
To appear in:
Journal of Physics and Chemistry of Solids
Received Date: 17 December 2017 Revised Date:
1 March 2018
Accepted Date: 2 March 2018
Please cite this article as: R. Cao, G. Quan, Z. Shi, T. Chen, Z. Luo, G. Zheng, Z. Hu, Synthesis and 3+ 3+ 3+ 3+ luminescence properties of La2Zr2O7:R (R = Sm , Bi , Sm /Bi ) phosphor, Journal of Physics and Chemistry of Solids (2018), doi: 10.1016/j.jpcs.2018.03.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis and luminescence properties of La2Zr2O7:R (R = Sm3+, Bi3+, Sm3+/Bi3+) phosphor Renping Cao*1, Guanjun Quan1, Zhihui Shi1, Ting Chen1, Zhiyang Luo2, Guotai Zheng1, Zuofu Hu1
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College of Mathematics and Physics, Jinggangshan University, Ji’an 343009, China
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College of Mechanical Manufacture and Automation, Jinggangshan University, Ji’an 343009, China *corresponding author: E-mail: [email protected]; Tel/fax: +86 796 8124959
Abstract: La2Zr2O7:R (R = Sm3+, Bi3+, Sm3+/Bi3+) phosphors are synthesized by solid-state reaction method in air. Blue emission band peaking at ~ 462 nm of La2Zr2O7:Bi3+ phosphor with excitation at 312 nm is observed in the
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range of 370 - 610 nm due to 3P1 → 1S0 transition of Bi3+ ion and D → 1S0 transition between Bi3+ and Zr4+ ions. La2Zr2O7:Sm3+ phosphor with excitation at 407 nm shows reddish orange light in the range of 550 - 750 nm owing
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to 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ion. Tunable emission from blue to white of La2Zr2O7:Sm3+, Bi3+ phosphor with excitation at 312 nm can be observed due to the changing Bi3+ or Sm3+ ion concentration. La2Zr2O7:Sm3+, Bi3+ phosphor with excitation at 407 nm only emits reddish orange because Bi3+ has no absorption at 407 nm. The energy transfer from Bi3+ to Sm3+ is discussed. The luminous mechanism is explained by the energy level diagrams of Bi3+ and Sm3+ ions.
1. Introduction
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Keywords: Phosphor; La2Zr2O7; Bi3+ ion; Sm3+ ion; Tunable emission
In the recent years, rare-earth doped luminescent materials have attracted much attention due to the applications in many fields such as cathode ray tubes, plasma display panels, light-emitting diodes,
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X-ray detectors, field emission displays, and fluorescent lamps [1-3]. In luminescent materials, except for luminescent active ions, varieties of hosts used to fabricate luminescent materials are also an
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important influence factor to the luminescence properties [4-6]. Rare-earth zirconates (Re2Zr2O7) with a pyrochlore structure have been extensively investigated in
recent years for their characteristic properties (e.g., excellent stability, magnetic, electronic, and optical properties) and potential applications in many fields (e.g., high temperature heating elements, oxidation catalysts, and host materials for luminescence centers) [7-10]. La2Zr2O7, which has excellent thermal and high phase stabilities, is one of the rare-earth zirconates and becomes a very promising host material for luminescence centers [11]. Up to now, the luminescent properties of rare-earth ion doped La2Zr2O7 have been reported widely. In 1999, Tezuka et al. researched the luminescence properties of Pr4+-doped La2Zr2O7 phosphor [12]. In 2006, Zhang et al. reported the synthesis and luminescence properties of Eu3+, Dy3+-doped La2Zr2O7 nanocrystal [7]. In 2015, Singh et al. reported the synthesis 1
ACCEPTED MANUSCRIPT and luminescence properties of La2Zr2O7:Gd3+ phosphor powder [8]. Sm3+ ion shows red emission in the range of 570- 750 nm and Bi3+ ion in some hosts may show emission in the range of 380- 650 nm. Tunable emission may be occurred by changing the Sm3+ or Bi3+ content. Energy transfer (ET) from Bi3+ to Sm3+ ions is helpful for the emission property improvement of phosphors. Thus, La2Zr2O7:Sm3+, Bi3+ phosphor is taken as an object of study, which has rarely been reported.
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In this work, a series of La2Zr2O7:R (R = Sm3+, Bi3+, Sm3+/Bi3+) phosphors are synthesized by high temperature solid-state reaction method in air. Their crystal structures and luminescence properties are investigated. Luminescence properties of La2Zr2O7:Sm3+, La2Zr2O7:Bi3+, and La2Zr2O7:Sm3+, Bi3+ phosphors are investigated, respectively. The influences of Bi3+ and Sm3+ ions concentration to
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luminescence properties are discussed. Tunable emission properties of La2Zr2O7:Sm3+, Bi3+ phosphor is researched with changing Bi3+ or Sm3+ ion content. The ET from Bi3+ to Sm3+ is discussed. The
2. Experimental section 2.1. Raw materials and synthesis
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luminous mechanisms of Bi3+ and Sm3+ ions are explained by their energy level diagrams.
All the chemicals (La2O3 (99.95%), ZrO2 (99.9%), Sm2O3 (99.95%), and Bi2O3 (99.99%)) are purchased from the Aladdin Chemical Reagent Company in Shanghai, China. All raw materials are not
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further purified. La2-xZr2O7:xBi3+ (x = 0, 0.5, 1, 2, 3, and 4 mol%), La2-yZr2O7:ySm3+ (x = 1, 2, 3, 4, 5, 6, and 7 mol%), and La1.95-xZr2O7:xBi3+, 5%Sm3+ (x = 0.5, 1, 2, 3, and 4 mol%) phosphors are synthesized by high temperature solid-state reaction method in air. The stoichiometric amount of raw
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materials (5g) are well ground in an agate mortar, then sintered at 650 ºC for 6 h, subsequently reground and sintered at 1350 ºC for 5 h in air. Repeated grindings are performed between two sintering
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processes to improve the homogeneity. All products are obtained after natural cooling to room temperature.
2.2. Measurements and characterization The crystal structures of all samples are checked by X-Ray Powder Diffraction (XRD) (Philips
Model PW1830) with Cu-Kα radiation at 40 kV and 40 mA at room temperature. The data are collected in the 2θ range of 10 - 90º. The size and morphology of the phosphors are measured by scanning electron microscopy (Phenom Prox SEM) with 15 kV. Energy Disperse Spectroscopy (EDS) is investigated via Phenom Prox EDS. Luminescence properties of samples are investigated by using a steady-state FLS980 spectrofluorimeter (Edinburgh Instruments, UK, Edinburgh) with a high spectral
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The unit cell of La2Zr2O7 in Fig. 1 is drawn on the basis of the Inorganic Crystal Structure Database (ICSD) #154752. La2Zr2O7 has a cubic crystal system. The space-group of La2Zr2O7 is Fd -3m (227) and its lattice parameters are a = 10.7930 Å, V = 1257.26 Å3, and Z = 8 [13]. The crystal structure of La2Zr2O7 is composed of [LaO8] and [ZrO6] coordination polyhedra [12-14]. La3+ ion is
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located within distorted cube and Zr4+ ion is located within trigonal antiprism. La3+ and Zr4+ ion sites can be substituted by other elements with similar ionic radii. According to the valence state and ionic
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radius similar principles (CN = 8) (La3+: ~ 1.16 Å, Zr3+: ~ 0.84 Å, Bi3+: ~ 1.17 Å, and Sm3+: ~ 1.08 Å) [15], it is inferred that Bi3+ and Sm3+ ions will replace for La3+ ion sites when they are doped into host La2Zr2O7 lattice.
According to XRD patterns of Joint Committee on Powder Diffraction Standards (JCPDS) card no. 71- 2363 (La2Zr2O7), La2Zr2O7, La2-xZr2O7:xBi3+ (x = 1 and 4 mol%), La2-yZr2O7:ySm3+ (y = 3 and 6
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mol%), and La1.92Zr2O7:3%Bi3+, 5%Sm3+ phosphors in Fig. 2, it can be confirmed the conformity of XRD patterns of these phosphors with the standard pattern of JCPDS card (no. 71- 2363). The XRD patterns of other La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%), La2-yZr2O7:ySm3+ (1 ≤ y ≤ 7 mol%), and
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La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors are not shown in Fig. 2, but their XRD patterns are also in line with that of JCPDS card (no. 71- 2363). We do not observe other crystalline
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phases in Fig. 2. X-ray diffraction showed single phase formation. It can be inferred that the doping of Bi3+ and Sm3+ ions does not cause significant influence on the La2Zr2O7 crystal structure. According to EDS spectrum and SEM image of La2Zr2O7:Bi3+, Sm3+ phosphor in Fig. 3, the
dopants (Bi3+ and Sm3+ ions) are doped into the host La2Zr2O7 lattice, the shape of phosphor is granular, and the size of phosphor is in the range of 200-300 nm. 3.2. Bi3+ or Sm3+-doped La2Zr2O7 phosphor Photoluminescence excitation (PLE) and photoluminescence (PL) spectra of La1.95Zr2O7:5%Sm3+ (λex = 407 nm and λem = 605 nm) phosphor at room temperature are shown in Fig. 4(a). La2Zr2O7:Sm3+ phosphor with excitation at 407 nm shows reddish orange light and its chromaticity coordinate is
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ACCEPTED MANUSCRIPT (0.5793, 0.4196). Many narrow PL bands (550 - 588 nm, 588 - 633 nm, 633 - 684 nm, and 700 - 750 nm) in the range of 550 - 750 nm are observed, which are attributed to the 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ion, respectively [16,17]. PLE spectrum of La2Zr2O7:Sm3+ phosphor monitored at 605 nm includes a series of PLE bands in the range of 210 - 550 nm. The PLE band in the range of 210 - 300 nm may be attributed to the O2- → Sm3+ charge transfer [18]. Many narrow PLE
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bands within the range 300 - 550 nm are assigned to the 6H5/2 → (4H9/2, 4F9/2, 6P7/2, 4F7/2, 6P5/2, 4G9/2, and 4I11/2) transitions of Sm3+ ions, respectively [19,20].
PLE and PL spectra of La1.99Zr2O7:1%Bi3+ (λex = 312 nm and λem = 462 nm) phosphor at room
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temperature are shown in Fig. 4(b). La2Zr2O7:Bi3+ phosphor with excitation at 312 nm shows blue light and its Commission internationale de l'Éclairage (CIE) chromaticity coordinate is about (0.1542, 0.1431). Emission of Bi3+ ion can be observed owing to the 3P1, 0 → 1S0 transitions and the 3P0 → 1S0
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transition mainly occurs at low temperatures. So, PL band peaking at ~ 462 nm of La2Zr2O7:Bi3+ phosphor in the range of 370 - 610 nm is attributed to the 3P1 → 1S0 electron transition of Bi3+ ion at the room temperature [21,22]. In addition, charge transfer transition between Bi3+ (6s2) and the Zr4+ (4d0) ions also exhibits very efficient luminescence, so, the emission in La2Zr2O7:Bi3+ can be assigned to D → 1S0 transition at the same time [23]. When monitored at 462 nm, PLE spectrum of La2Zr2O7:Bi3+
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phosphor contains two PLE bands peaking at ~ 252 and 312 nm in the range of 220 - 310 nm, which are assigned to the O2- → Bi3+ charge transfer (~ 252 nm) and the 1S0 → 3P1 electron transition of Bi3+ ion (~ 312 nm), respectively [24]. In addition, it can be found that there is an overlap between PL band
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Bi3+ ion and PLE band of Sm3+ ion in the range of 380-550 nm, which indicates that ET between Bi3+ and Sm3+ ions is possible formed when Bi3+ and Sm3+ ions are co-doped into host lattice.
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QEs of La2Zr2O7:R (R = Sm3+ or Bi3+) phosphor are measured directily and its computational formula is as follows:
η = ∫Ldirect / (∫Ewithout - ∫Edirect)
(1)
where η is the quantum yield. Ldirect is the complete emission spectrum of the sample being measured, collected using the sphere. Edirect is the emission spectra of the excitation light, recorded with the sample in place, and collected using the sphere. Ewithout is the emission spectra of the excitation light, recorded with the equipment blank sample in place, and collected using the sphere. QEs of La2Zr2O7:R (R = Sm3+ or Bi3+) phosphor are 25.2% and 32.6%, respectively. Fig. 5 shows PL spectra of La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%) (λex = 312 nm) and
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ACCEPTED MANUSCRIPT La2-yZr2O7:ySm3+ (1 ≤ y ≤ 7 mol%) (λex = 407 nm) phosphors and the relations between PL intensity and Bi3+ or Sm3+ ion concentration at room temperature. PL spectral shape and position show the same except PL intensity with increasing Bi3+ or Sm3+ ion concentration. PL intensity increases at first with increasing Bi3+ or Sm3+ ion concentration and then decreases with further increasing Bi3+ or Sm3+ ion concentration. The former observation is assigned to the distance between Bi3+/Sm3+ ion ions, and the
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intensity is proportional to Bi3+ or Sm3+ ion concentration. The latter observation is due to the concentration quenching of Bi3+ or Sm3+ ion. Therefore, the optimal Bi3+ and Sm3+ ion concentrations are about 1mol% and 5mol%, respectively. According to the formula suggested by Blasse et al [25]:
(2)
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Rc ≈ 2[3V/(4πXcN)]1/3
where V is the unit cell volume of host lattice, Xc is the critical concentration, N is the number of sites available for the dopant in the unit cell. Here, V, Xc, and N values of Bi3+ and Sm3+ ions are (1257.26,
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0.01, and 8) and (1257.26, 0.05, and 8), respectively. So, the critical transfer distances of Bi3+ and Sm3+ ions in host lattice are about 31.18 and 18.17 Å, respectively. 3.3. Bi3+ and Sm3+ co-doped La2Zr2O7 phosphor
Fig. 6 shows PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors at room temperature (λex = 312 nm) and the CIE chromaticity diagram. La2Zr2O7:xBi3+, 5%Sm3+ phosphor with
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excitation at 312 nm shows a systematically tunable emission from blue to white light with increasing Bi3+ ion concentration in the range of 0.5 - 4%. As shown in Table 1, the corresponding CIE chromaticity coordinates are changed from (0.1635, 0.1558) to (0.2577, 0.2245). PL spectral shape and
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peak positions of La1.95-xZr2O7:xBi3+, 5%Sm3+ phosphors are the same with changing Bi3+ ion concentration. PL intensity increases with increasing Bi3+ ion concentration from 0 to 1.0 mol%
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because of ET from Bi3+ to Sm3+, and decreases with further increasing Bi3+ ion concentration due to concentration quenching (CQ). The optimal Bi3+ content is 1.0 mol%. The ET may be explained by PLE and PL spectra in Fig. 4. The CQ may be estimated by the critical distance (Rc), which can be calculated by the equation (1). V and N are 1257.26 Å3 and 8, respectively. Xc is 0.06, which is the sum of Sm3+ ang Bi3+. So, the Rc is determined to be ~ 17.1 Å. So, the nonradiative ET mechanism from Bi3+ to Sm3+ ions may belong to the multipolar interaction because the Rc value is much longer than 5 Å. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperature (λex = 407 nm) and the relation between PL intensity and Bi3+ ion concentration are shown in Fig. 7. The
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Now we explain the luminous mechanism according to the energy level diagrams of Bi3+ and Sm3+ ions in Fig. 8. Bi3+ ion has the [Xe]4f145d106s2 electronic configuration. The ground state 1S0 derives from the 6s2 configuration and four excited states 3P0, 1, 2 and 1P1 come from the 6s6p electronic configuration [26]. The 1S0 → 3P1 transition may be allowed due to the spin–orbit mixing of the 3P1 and P1 states, so, PLE band peaking at 312 nm in Fig. 4(a) is assigned to the 1S0 → 3P1 transition. Broad
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PL band peaking in the region from near ultraviolet (UV) to yellow light with excitation UV light can
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be observed owing to the 3P1, 0 → 1S0 transitions of Bi3+ ion in different host. PL band is dominated by the 3P0 → 1S0 transition at low temperatures because the 3P0 state acts as an optical trap. With increasing temperature, thermal population of the higher energy 3P1 state results in the occurrence of the 3P1 → 1S0 transition. In addition, charge transfer transition between Bi3+ (6s2) and the Zr4+ (4d0) ions also exhibits very efficient luminescence. Thus, PL band peaking at ~ 462 nm in Fig. 4(a) is
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attributed to the 3P1 → 1S0 transition of Bi3+ ion and D → 1S0 transition between Bi3+ and Zr4+ ions. In Sm3+ ion with 4f5 configuration, the absorption bands are attributed to f - f electron transition from ground state 6H5/2 to excited states, and narrow characteristic emission lines in Fig. 4(b) are due to 4G5/2
4. Conclusions
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→ 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ion [27,28].
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In summary, La2Zr2O7:Bi3+, La2Zr2O7:Sm3+, and La2Zr2O7:Sm3+, Bi3+ phosphors are synthesized by high temperature solid-state reaction method in air. X-ray diffraction confirms that all samples are single phase formation. La2Zr2O7:Bi3+ phosphor with excitation at 312 nm shows blue light with PL band peaking at ~ 462 nm in the range of 370 - 610 nm due to the 3P1 → 1S0 electron transition of Bi3+ ion and D → 1S0 transition between Bi3+ and Zr4+ ions. La2Zr2O7:Sm3+ phosphor with excitation at 407 nm shows reddish orange light in the range of 550 - 750 nm because of the 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ion. The optimal Bi3+ and Sm3+ ions concentrations are about 1 mol% and 5 mol%, respectively. La2Zr2O7:Sm3+, Bi3+ phosphor with excitation at 312 nm shows a systematically tunable emission with changing Bi3+ or Sm3+ ion concentration and only emits reddish
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ACCEPTED MANUSCRIPT orange light under excitation at 407 nm. The luminous mechanisms of Bi3+ and Sm3+ ions are explained by their energy level diagrams. Acknowledgment This work was financially supported by the National Natural Science Foundation of China (No.
Foundation of Jiang’xi Educational Committee (No. GJJ160748). References [1] J. Zhao, C. Guo, T. Li, X. Su, N. Zhang, J. Chen, Dyes Pigments. 132 (2016) 159–166.
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11464021), Natural Science Foundation of Jiangxi Province of China (No. 20171BAB201018), and
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[11] M. Pokhrel, M.G. Brik, Y. Mao, J. Am. Ceram. Soc. 98(10) (2015) 3192–3201. [12] K. Tezuka, Y. Hinatsu, J. Solid State Chem. 143 (1999) 140-143. [13] M. Uno, A. Kosuga, M. Okui, K. Horisaka, H. Muta, K. Kurosaki, S. Yamanaka, J. Alloys Compd. 420(420) (2006) 291-297.
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[14] N. Zotov, A. Guignard, G. Mauer, R. Vaßen, J. Am. Ceram. Soc. 99(3) (2016) 1086–1091. [15] R.D. Shannon, Acta Cryst. A 32 (1976) 751-767. [16] R. Cao, G. Chen, X. Yu, P. Tang, Z. Luo, S. Guo, G. Zheng, Mater. Chem. Phys. 171 (2016) 222-226.
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[17] Q. Xu, D. Xu, J. Sun, Opt. Mater. 42 (2015) 210-214. [18] C. Gheorghe, S. Hau, L. Gheorghe, F. Voicu, M. Greculeasa, A. Achim, M. Enculescu, J. Lumin. 186 (2017) 175-182. [19] G. Liu, B. Jacquier, Spectroscopic Properties of Rare Earths in Optical Materials, Springer, Berlin, 2005. [20] R. Cao, J. Huang, X. Ceng, Z. Hu, T. Chen, W. Hu, X. Zhang, Optik. 135 (2017) 124-128. [21] H.T. Sun, J.J. Zhou, J.R. Qiu, Prog. Mater Sci. 64 (2014) 1–72. [22] R. Cao, G. Quan, Z. Shi, Z. Luo, Q. Hu, S. Guo, J. Lumin. 181 (2017) 332-336. [23] A.M. Srivastava, W.W. Beers, J. Lumin. 81 (1999) 293 - 300. [24] V. Babin, K. Chernenko, P. Demchenko, E. Mihokova, M. Nikl, I. Pashuk, T. Shalapska, A. Voloshinovskii, S. Zazubovich, J. Lumin. 176 (2016) 324-330. [25] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer-Verlag. Berlin-Heidelberg. 1994. [26] H. Zhou, M. Jiang, Y. Jin, RSC Adv. 4 (2014) 45786-45790.
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ACCEPTED MANUSCRIPT Figure captions Fig. 1. The unit cell of La2Zr2O7 drawn on the basis of ICSD #154752, [ZrO6] and [LaO8] polyhedra. Fig. 2. XRD patterns of JCPDS card no. 71- 2363 (La2Zr2O7), La2Zr2O7, La2-xZr2O7:xBi3+ (x = 1 and 4 mol%) La2-yZr2O7:ySm3+ (x = 3 and 6 mol%), and La1.92Zr2O7:3%Bi3+, 5%Sm3+ phosphors. Fig. 3. EDS spectrum and SEM image of La2Zr2O7:Bi3+, Sm3+ phosphor.
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Fig. 4. PLE and PL spectra of (a) La1.95Zr2O7:5%Sm3+ (λex = 407 nm and λem = 605 nm) and (b) La1.99Zr2O7:1%Bi3+ (λex = 312 nm and λem = 462 nm) phosphors at room temperture. The inset: The corresponding CIE chromaticity diagrams.
Fig. 5(a) PL spectra of La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm). (b) PL
relations between PL intensity and Bi3+ or Sm3+ ion concentration.
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spectra of La2-yZr2O7:ySm3+ (1 ≤ y ≤ 7 mol%) phosphors at room temperture (λex = 407 nm). The inset: The
and the CIE chromaticity diagram.
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Fig. 6. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm)
Fig. 7. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 407 nm). The inset: The relation between PL intensity and Bi3+ ion concentration.
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Fig. 8. The energy level diagrams of Bi3+ and Sm3+ ions.
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Figures
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Fig. 1. The unit cell of La2Zr2O7 drawn on the basis of ICSD #154752, [ZrO6] and [LaO8] polyhedra.
Fig. 2. XRD patterns of JCPDS card no. 71- 2363 (La2Zr2O7), La2Zr2O7, La2-xZr2O7:xBi3+ (x = 1 and 4 mol%)
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La2-yZr2O7:ySm3+ (x = 3 and 6 mol%), and La1.92Zr2O7:3%Bi3+, 5%Sm3+ phosphors.
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Fig. 3. EDS spectrum and SEM image of La2Zr2O7:Bi3+, Sm3+ phosphor.
Fig. 4. PLE and PL spectra of (a) La1.95Zr2O7:5%Sm3+ (λex = 407 nm and λem = 605 nm) and (b)
La1.99Zr2O7:1%Bi3+ (λex = 312 nm and λem = 462 nm) phosphors at room temperture. The inset: The corresponding CIE chromaticity diagrams.
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Fig. 5(a) PL spectra of La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm). (b) PL spectra of La2-yZr2O7:ySm3+ (1 ≤ y ≤ 7 mol%) phosphors at room temperture (λex = 407 nm). The inset: The
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relations between PL intensity and Bi3+ or Sm3+ ion concentration.
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Fig. 6. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm)
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and the CIE chromaticity diagram.
Fig. 7. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 407 nm). The inset: The relation between PL intensity and Bi3+ ion concentration.
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Fig. 8. The energy level diagrams of Bi3+ and Sm3+ ions.
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ACCEPTED MANUSCRIPT Table Table 1. The CIE chromaticity coordinates of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors CIE chromaticity coordinate x
y
0.5
0.1635
0.1558
1.0
0.1640
0.1568
2.0
0.1704
0.1583
3.0
0.1916
0.1744
4.0
0.2577
0.2245
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(mol%)
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Bi3+
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ACCEPTED MANUSCRIPT Highlights 1. La2Zr2O7:Sm3+, Bi3+ phosphors are synthesized by solid-state reaction method in air. 2. La2Zr2O7:Bi3+, La2Zr2O7:Sm3+, and La2Zr2O7:Sm3+, Bi3+ phosphors are compared and analyzed.
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3. The luminous mechanism is explained by the energy level diagrams of Bi3+ and Sm3+ ions.
S0022-3697(17)32441-1
DOI:
10.1016/j.jpcs.2018.03.002
Reference:
PCS 8472
To appear in:
Journal of Physics and Chemistry of Solids
Received Date: 17 December 2017 Revised Date:
1 March 2018
Accepted Date: 2 March 2018
Please cite this article as: R. Cao, G. Quan, Z. Shi, T. Chen, Z. Luo, G. Zheng, Z. Hu, Synthesis and 3+ 3+ 3+ 3+ luminescence properties of La2Zr2O7:R (R = Sm , Bi , Sm /Bi ) phosphor, Journal of Physics and Chemistry of Solids (2018), doi: 10.1016/j.jpcs.2018.03.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis and luminescence properties of La2Zr2O7:R (R = Sm3+, Bi3+, Sm3+/Bi3+) phosphor Renping Cao*1, Guanjun Quan1, Zhihui Shi1, Ting Chen1, Zhiyang Luo2, Guotai Zheng1, Zuofu Hu1
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College of Mathematics and Physics, Jinggangshan University, Ji’an 343009, China
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College of Mechanical Manufacture and Automation, Jinggangshan University, Ji’an 343009, China *corresponding author: E-mail: [email protected]; Tel/fax: +86 796 8124959
Abstract: La2Zr2O7:R (R = Sm3+, Bi3+, Sm3+/Bi3+) phosphors are synthesized by solid-state reaction method in air. Blue emission band peaking at ~ 462 nm of La2Zr2O7:Bi3+ phosphor with excitation at 312 nm is observed in the
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range of 370 - 610 nm due to 3P1 → 1S0 transition of Bi3+ ion and D → 1S0 transition between Bi3+ and Zr4+ ions. La2Zr2O7:Sm3+ phosphor with excitation at 407 nm shows reddish orange light in the range of 550 - 750 nm owing
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to 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ion. Tunable emission from blue to white of La2Zr2O7:Sm3+, Bi3+ phosphor with excitation at 312 nm can be observed due to the changing Bi3+ or Sm3+ ion concentration. La2Zr2O7:Sm3+, Bi3+ phosphor with excitation at 407 nm only emits reddish orange because Bi3+ has no absorption at 407 nm. The energy transfer from Bi3+ to Sm3+ is discussed. The luminous mechanism is explained by the energy level diagrams of Bi3+ and Sm3+ ions.
1. Introduction
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Keywords: Phosphor; La2Zr2O7; Bi3+ ion; Sm3+ ion; Tunable emission
In the recent years, rare-earth doped luminescent materials have attracted much attention due to the applications in many fields such as cathode ray tubes, plasma display panels, light-emitting diodes,
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X-ray detectors, field emission displays, and fluorescent lamps [1-3]. In luminescent materials, except for luminescent active ions, varieties of hosts used to fabricate luminescent materials are also an
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important influence factor to the luminescence properties [4-6]. Rare-earth zirconates (Re2Zr2O7) with a pyrochlore structure have been extensively investigated in
recent years for their characteristic properties (e.g., excellent stability, magnetic, electronic, and optical properties) and potential applications in many fields (e.g., high temperature heating elements, oxidation catalysts, and host materials for luminescence centers) [7-10]. La2Zr2O7, which has excellent thermal and high phase stabilities, is one of the rare-earth zirconates and becomes a very promising host material for luminescence centers [11]. Up to now, the luminescent properties of rare-earth ion doped La2Zr2O7 have been reported widely. In 1999, Tezuka et al. researched the luminescence properties of Pr4+-doped La2Zr2O7 phosphor [12]. In 2006, Zhang et al. reported the synthesis and luminescence properties of Eu3+, Dy3+-doped La2Zr2O7 nanocrystal [7]. In 2015, Singh et al. reported the synthesis 1
ACCEPTED MANUSCRIPT and luminescence properties of La2Zr2O7:Gd3+ phosphor powder [8]. Sm3+ ion shows red emission in the range of 570- 750 nm and Bi3+ ion in some hosts may show emission in the range of 380- 650 nm. Tunable emission may be occurred by changing the Sm3+ or Bi3+ content. Energy transfer (ET) from Bi3+ to Sm3+ ions is helpful for the emission property improvement of phosphors. Thus, La2Zr2O7:Sm3+, Bi3+ phosphor is taken as an object of study, which has rarely been reported.
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In this work, a series of La2Zr2O7:R (R = Sm3+, Bi3+, Sm3+/Bi3+) phosphors are synthesized by high temperature solid-state reaction method in air. Their crystal structures and luminescence properties are investigated. Luminescence properties of La2Zr2O7:Sm3+, La2Zr2O7:Bi3+, and La2Zr2O7:Sm3+, Bi3+ phosphors are investigated, respectively. The influences of Bi3+ and Sm3+ ions concentration to
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luminescence properties are discussed. Tunable emission properties of La2Zr2O7:Sm3+, Bi3+ phosphor is researched with changing Bi3+ or Sm3+ ion content. The ET from Bi3+ to Sm3+ is discussed. The
2. Experimental section 2.1. Raw materials and synthesis
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luminous mechanisms of Bi3+ and Sm3+ ions are explained by their energy level diagrams.
All the chemicals (La2O3 (99.95%), ZrO2 (99.9%), Sm2O3 (99.95%), and Bi2O3 (99.99%)) are purchased from the Aladdin Chemical Reagent Company in Shanghai, China. All raw materials are not
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further purified. La2-xZr2O7:xBi3+ (x = 0, 0.5, 1, 2, 3, and 4 mol%), La2-yZr2O7:ySm3+ (x = 1, 2, 3, 4, 5, 6, and 7 mol%), and La1.95-xZr2O7:xBi3+, 5%Sm3+ (x = 0.5, 1, 2, 3, and 4 mol%) phosphors are synthesized by high temperature solid-state reaction method in air. The stoichiometric amount of raw
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materials (5g) are well ground in an agate mortar, then sintered at 650 ºC for 6 h, subsequently reground and sintered at 1350 ºC for 5 h in air. Repeated grindings are performed between two sintering
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processes to improve the homogeneity. All products are obtained after natural cooling to room temperature.
2.2. Measurements and characterization The crystal structures of all samples are checked by X-Ray Powder Diffraction (XRD) (Philips
Model PW1830) with Cu-Kα radiation at 40 kV and 40 mA at room temperature. The data are collected in the 2θ range of 10 - 90º. The size and morphology of the phosphors are measured by scanning electron microscopy (Phenom Prox SEM) with 15 kV. Energy Disperse Spectroscopy (EDS) is investigated via Phenom Prox EDS. Luminescence properties of samples are investigated by using a steady-state FLS980 spectrofluorimeter (Edinburgh Instruments, UK, Edinburgh) with a high spectral
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The unit cell of La2Zr2O7 in Fig. 1 is drawn on the basis of the Inorganic Crystal Structure Database (ICSD) #154752. La2Zr2O7 has a cubic crystal system. The space-group of La2Zr2O7 is Fd -3m (227) and its lattice parameters are a = 10.7930 Å, V = 1257.26 Å3, and Z = 8 [13]. The crystal structure of La2Zr2O7 is composed of [LaO8] and [ZrO6] coordination polyhedra [12-14]. La3+ ion is
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located within distorted cube and Zr4+ ion is located within trigonal antiprism. La3+ and Zr4+ ion sites can be substituted by other elements with similar ionic radii. According to the valence state and ionic
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radius similar principles (CN = 8) (La3+: ~ 1.16 Å, Zr3+: ~ 0.84 Å, Bi3+: ~ 1.17 Å, and Sm3+: ~ 1.08 Å) [15], it is inferred that Bi3+ and Sm3+ ions will replace for La3+ ion sites when they are doped into host La2Zr2O7 lattice.
According to XRD patterns of Joint Committee on Powder Diffraction Standards (JCPDS) card no. 71- 2363 (La2Zr2O7), La2Zr2O7, La2-xZr2O7:xBi3+ (x = 1 and 4 mol%), La2-yZr2O7:ySm3+ (y = 3 and 6
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mol%), and La1.92Zr2O7:3%Bi3+, 5%Sm3+ phosphors in Fig. 2, it can be confirmed the conformity of XRD patterns of these phosphors with the standard pattern of JCPDS card (no. 71- 2363). The XRD patterns of other La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%), La2-yZr2O7:ySm3+ (1 ≤ y ≤ 7 mol%), and
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La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors are not shown in Fig. 2, but their XRD patterns are also in line with that of JCPDS card (no. 71- 2363). We do not observe other crystalline
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phases in Fig. 2. X-ray diffraction showed single phase formation. It can be inferred that the doping of Bi3+ and Sm3+ ions does not cause significant influence on the La2Zr2O7 crystal structure. According to EDS spectrum and SEM image of La2Zr2O7:Bi3+, Sm3+ phosphor in Fig. 3, the
dopants (Bi3+ and Sm3+ ions) are doped into the host La2Zr2O7 lattice, the shape of phosphor is granular, and the size of phosphor is in the range of 200-300 nm. 3.2. Bi3+ or Sm3+-doped La2Zr2O7 phosphor Photoluminescence excitation (PLE) and photoluminescence (PL) spectra of La1.95Zr2O7:5%Sm3+ (λex = 407 nm and λem = 605 nm) phosphor at room temperature are shown in Fig. 4(a). La2Zr2O7:Sm3+ phosphor with excitation at 407 nm shows reddish orange light and its chromaticity coordinate is
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bands within the range 300 - 550 nm are assigned to the 6H5/2 → (4H9/2, 4F9/2, 6P7/2, 4F7/2, 6P5/2, 4G9/2, and 4I11/2) transitions of Sm3+ ions, respectively [19,20].
PLE and PL spectra of La1.99Zr2O7:1%Bi3+ (λex = 312 nm and λem = 462 nm) phosphor at room
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temperature are shown in Fig. 4(b). La2Zr2O7:Bi3+ phosphor with excitation at 312 nm shows blue light and its Commission internationale de l'Éclairage (CIE) chromaticity coordinate is about (0.1542, 0.1431). Emission of Bi3+ ion can be observed owing to the 3P1, 0 → 1S0 transitions and the 3P0 → 1S0
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transition mainly occurs at low temperatures. So, PL band peaking at ~ 462 nm of La2Zr2O7:Bi3+ phosphor in the range of 370 - 610 nm is attributed to the 3P1 → 1S0 electron transition of Bi3+ ion at the room temperature [21,22]. In addition, charge transfer transition between Bi3+ (6s2) and the Zr4+ (4d0) ions also exhibits very efficient luminescence, so, the emission in La2Zr2O7:Bi3+ can be assigned to D → 1S0 transition at the same time [23]. When monitored at 462 nm, PLE spectrum of La2Zr2O7:Bi3+
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phosphor contains two PLE bands peaking at ~ 252 and 312 nm in the range of 220 - 310 nm, which are assigned to the O2- → Bi3+ charge transfer (~ 252 nm) and the 1S0 → 3P1 electron transition of Bi3+ ion (~ 312 nm), respectively [24]. In addition, it can be found that there is an overlap between PL band
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Bi3+ ion and PLE band of Sm3+ ion in the range of 380-550 nm, which indicates that ET between Bi3+ and Sm3+ ions is possible formed when Bi3+ and Sm3+ ions are co-doped into host lattice.
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QEs of La2Zr2O7:R (R = Sm3+ or Bi3+) phosphor are measured directily and its computational formula is as follows:
η = ∫Ldirect / (∫Ewithout - ∫Edirect)
(1)
where η is the quantum yield. Ldirect is the complete emission spectrum of the sample being measured, collected using the sphere. Edirect is the emission spectra of the excitation light, recorded with the sample in place, and collected using the sphere. Ewithout is the emission spectra of the excitation light, recorded with the equipment blank sample in place, and collected using the sphere. QEs of La2Zr2O7:R (R = Sm3+ or Bi3+) phosphor are 25.2% and 32.6%, respectively. Fig. 5 shows PL spectra of La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%) (λex = 312 nm) and
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intensity is proportional to Bi3+ or Sm3+ ion concentration. The latter observation is due to the concentration quenching of Bi3+ or Sm3+ ion. Therefore, the optimal Bi3+ and Sm3+ ion concentrations are about 1mol% and 5mol%, respectively. According to the formula suggested by Blasse et al [25]:
(2)
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Rc ≈ 2[3V/(4πXcN)]1/3
where V is the unit cell volume of host lattice, Xc is the critical concentration, N is the number of sites available for the dopant in the unit cell. Here, V, Xc, and N values of Bi3+ and Sm3+ ions are (1257.26,
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0.01, and 8) and (1257.26, 0.05, and 8), respectively. So, the critical transfer distances of Bi3+ and Sm3+ ions in host lattice are about 31.18 and 18.17 Å, respectively. 3.3. Bi3+ and Sm3+ co-doped La2Zr2O7 phosphor
Fig. 6 shows PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors at room temperature (λex = 312 nm) and the CIE chromaticity diagram. La2Zr2O7:xBi3+, 5%Sm3+ phosphor with
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excitation at 312 nm shows a systematically tunable emission from blue to white light with increasing Bi3+ ion concentration in the range of 0.5 - 4%. As shown in Table 1, the corresponding CIE chromaticity coordinates are changed from (0.1635, 0.1558) to (0.2577, 0.2245). PL spectral shape and
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peak positions of La1.95-xZr2O7:xBi3+, 5%Sm3+ phosphors are the same with changing Bi3+ ion concentration. PL intensity increases with increasing Bi3+ ion concentration from 0 to 1.0 mol%
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because of ET from Bi3+ to Sm3+, and decreases with further increasing Bi3+ ion concentration due to concentration quenching (CQ). The optimal Bi3+ content is 1.0 mol%. The ET may be explained by PLE and PL spectra in Fig. 4. The CQ may be estimated by the critical distance (Rc), which can be calculated by the equation (1). V and N are 1257.26 Å3 and 8, respectively. Xc is 0.06, which is the sum of Sm3+ ang Bi3+. So, the Rc is determined to be ~ 17.1 Å. So, the nonradiative ET mechanism from Bi3+ to Sm3+ ions may belong to the multipolar interaction because the Rc value is much longer than 5 Å. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperature (λex = 407 nm) and the relation between PL intensity and Bi3+ ion concentration are shown in Fig. 7. The
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Now we explain the luminous mechanism according to the energy level diagrams of Bi3+ and Sm3+ ions in Fig. 8. Bi3+ ion has the [Xe]4f145d106s2 electronic configuration. The ground state 1S0 derives from the 6s2 configuration and four excited states 3P0, 1, 2 and 1P1 come from the 6s6p electronic configuration [26]. The 1S0 → 3P1 transition may be allowed due to the spin–orbit mixing of the 3P1 and P1 states, so, PLE band peaking at 312 nm in Fig. 4(a) is assigned to the 1S0 → 3P1 transition. Broad
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PL band peaking in the region from near ultraviolet (UV) to yellow light with excitation UV light can
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be observed owing to the 3P1, 0 → 1S0 transitions of Bi3+ ion in different host. PL band is dominated by the 3P0 → 1S0 transition at low temperatures because the 3P0 state acts as an optical trap. With increasing temperature, thermal population of the higher energy 3P1 state results in the occurrence of the 3P1 → 1S0 transition. In addition, charge transfer transition between Bi3+ (6s2) and the Zr4+ (4d0) ions also exhibits very efficient luminescence. Thus, PL band peaking at ~ 462 nm in Fig. 4(a) is
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attributed to the 3P1 → 1S0 transition of Bi3+ ion and D → 1S0 transition between Bi3+ and Zr4+ ions. In Sm3+ ion with 4f5 configuration, the absorption bands are attributed to f - f electron transition from ground state 6H5/2 to excited states, and narrow characteristic emission lines in Fig. 4(b) are due to 4G5/2
4. Conclusions
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→ 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ion [27,28].
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In summary, La2Zr2O7:Bi3+, La2Zr2O7:Sm3+, and La2Zr2O7:Sm3+, Bi3+ phosphors are synthesized by high temperature solid-state reaction method in air. X-ray diffraction confirms that all samples are single phase formation. La2Zr2O7:Bi3+ phosphor with excitation at 312 nm shows blue light with PL band peaking at ~ 462 nm in the range of 370 - 610 nm due to the 3P1 → 1S0 electron transition of Bi3+ ion and D → 1S0 transition between Bi3+ and Zr4+ ions. La2Zr2O7:Sm3+ phosphor with excitation at 407 nm shows reddish orange light in the range of 550 - 750 nm because of the 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, and 11/2) transitions of Sm3+ ion. The optimal Bi3+ and Sm3+ ions concentrations are about 1 mol% and 5 mol%, respectively. La2Zr2O7:Sm3+, Bi3+ phosphor with excitation at 312 nm shows a systematically tunable emission with changing Bi3+ or Sm3+ ion concentration and only emits reddish
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ACCEPTED MANUSCRIPT orange light under excitation at 407 nm. The luminous mechanisms of Bi3+ and Sm3+ ions are explained by their energy level diagrams. Acknowledgment This work was financially supported by the National Natural Science Foundation of China (No.
Foundation of Jiang’xi Educational Committee (No. GJJ160748). References [1] J. Zhao, C. Guo, T. Li, X. Su, N. Zhang, J. Chen, Dyes Pigments. 132 (2016) 159–166.
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11464021), Natural Science Foundation of Jiangxi Province of China (No. 20171BAB201018), and
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[3] Z. Xia, Q. Liu, Prog. Mater Sci. 84 (2016) 59–117.
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[11] M. Pokhrel, M.G. Brik, Y. Mao, J. Am. Ceram. Soc. 98(10) (2015) 3192–3201. [12] K. Tezuka, Y. Hinatsu, J. Solid State Chem. 143 (1999) 140-143. [13] M. Uno, A. Kosuga, M. Okui, K. Horisaka, H. Muta, K. Kurosaki, S. Yamanaka, J. Alloys Compd. 420(420) (2006) 291-297.
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[14] N. Zotov, A. Guignard, G. Mauer, R. Vaßen, J. Am. Ceram. Soc. 99(3) (2016) 1086–1091. [15] R.D. Shannon, Acta Cryst. A 32 (1976) 751-767. [16] R. Cao, G. Chen, X. Yu, P. Tang, Z. Luo, S. Guo, G. Zheng, Mater. Chem. Phys. 171 (2016) 222-226.
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[17] Q. Xu, D. Xu, J. Sun, Opt. Mater. 42 (2015) 210-214. [18] C. Gheorghe, S. Hau, L. Gheorghe, F. Voicu, M. Greculeasa, A. Achim, M. Enculescu, J. Lumin. 186 (2017) 175-182. [19] G. Liu, B. Jacquier, Spectroscopic Properties of Rare Earths in Optical Materials, Springer, Berlin, 2005. [20] R. Cao, J. Huang, X. Ceng, Z. Hu, T. Chen, W. Hu, X. Zhang, Optik. 135 (2017) 124-128. [21] H.T. Sun, J.J. Zhou, J.R. Qiu, Prog. Mater Sci. 64 (2014) 1–72. [22] R. Cao, G. Quan, Z. Shi, Z. Luo, Q. Hu, S. Guo, J. Lumin. 181 (2017) 332-336. [23] A.M. Srivastava, W.W. Beers, J. Lumin. 81 (1999) 293 - 300. [24] V. Babin, K. Chernenko, P. Demchenko, E. Mihokova, M. Nikl, I. Pashuk, T. Shalapska, A. Voloshinovskii, S. Zazubovich, J. Lumin. 176 (2016) 324-330. [25] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer-Verlag. Berlin-Heidelberg. 1994. [26] H. Zhou, M. Jiang, Y. Jin, RSC Adv. 4 (2014) 45786-45790.
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[28] N. Ben Hassen, M. Ferhi, K. Horchani-Naifer, M. Férid, Opt. Mater. 46 (2015) 355-360.
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ACCEPTED MANUSCRIPT Figure captions Fig. 1. The unit cell of La2Zr2O7 drawn on the basis of ICSD #154752, [ZrO6] and [LaO8] polyhedra. Fig. 2. XRD patterns of JCPDS card no. 71- 2363 (La2Zr2O7), La2Zr2O7, La2-xZr2O7:xBi3+ (x = 1 and 4 mol%) La2-yZr2O7:ySm3+ (x = 3 and 6 mol%), and La1.92Zr2O7:3%Bi3+, 5%Sm3+ phosphors. Fig. 3. EDS spectrum and SEM image of La2Zr2O7:Bi3+, Sm3+ phosphor.
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Fig. 4. PLE and PL spectra of (a) La1.95Zr2O7:5%Sm3+ (λex = 407 nm and λem = 605 nm) and (b) La1.99Zr2O7:1%Bi3+ (λex = 312 nm and λem = 462 nm) phosphors at room temperture. The inset: The corresponding CIE chromaticity diagrams.
Fig. 5(a) PL spectra of La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm). (b) PL
relations between PL intensity and Bi3+ or Sm3+ ion concentration.
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spectra of La2-yZr2O7:ySm3+ (1 ≤ y ≤ 7 mol%) phosphors at room temperture (λex = 407 nm). The inset: The
and the CIE chromaticity diagram.
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Fig. 6. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm)
Fig. 7. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 407 nm). The inset: The relation between PL intensity and Bi3+ ion concentration.
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Fig. 8. The energy level diagrams of Bi3+ and Sm3+ ions.
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Figures
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Fig. 1. The unit cell of La2Zr2O7 drawn on the basis of ICSD #154752, [ZrO6] and [LaO8] polyhedra.
Fig. 2. XRD patterns of JCPDS card no. 71- 2363 (La2Zr2O7), La2Zr2O7, La2-xZr2O7:xBi3+ (x = 1 and 4 mol%)
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La2-yZr2O7:ySm3+ (x = 3 and 6 mol%), and La1.92Zr2O7:3%Bi3+, 5%Sm3+ phosphors.
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Fig. 3. EDS spectrum and SEM image of La2Zr2O7:Bi3+, Sm3+ phosphor.
Fig. 4. PLE and PL spectra of (a) La1.95Zr2O7:5%Sm3+ (λex = 407 nm and λem = 605 nm) and (b)
La1.99Zr2O7:1%Bi3+ (λex = 312 nm and λem = 462 nm) phosphors at room temperture. The inset: The corresponding CIE chromaticity diagrams.
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Fig. 5(a) PL spectra of La2-xZr2O7:xBi3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm). (b) PL spectra of La2-yZr2O7:ySm3+ (1 ≤ y ≤ 7 mol%) phosphors at room temperture (λex = 407 nm). The inset: The
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relations between PL intensity and Bi3+ or Sm3+ ion concentration.
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Fig. 6. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 312 nm)
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and the CIE chromaticity diagram.
Fig. 7. PL spectra of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0 ≤ x ≤ 4 mol%) phosphors at room temperture (λex = 407 nm). The inset: The relation between PL intensity and Bi3+ ion concentration.
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Fig. 8. The energy level diagrams of Bi3+ and Sm3+ ions.
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ACCEPTED MANUSCRIPT Table Table 1. The CIE chromaticity coordinates of La1.95-xZr2O7:xBi3+, 5%Sm3+ (0.5 ≤ x ≤ 4 mol%) phosphors CIE chromaticity coordinate x
y
0.5
0.1635
0.1558
1.0
0.1640
0.1568
2.0
0.1704
0.1583
3.0
0.1916
0.1744
4.0
0.2577
0.2245
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(mol%)
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Bi3+
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ACCEPTED MANUSCRIPT Highlights 1. La2Zr2O7:Sm3+, Bi3+ phosphors are synthesized by solid-state reaction method in air. 2. La2Zr2O7:Bi3+, La2Zr2O7:Sm3+, and La2Zr2O7:Sm3+, Bi3+ phosphors are compared and analyzed.
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3. The luminous mechanism is explained by the energy level diagrams of Bi3+ and Sm3+ ions.