- Email: [email protected]
Luminescent properties and energy transfer in novel single-phase multicolor tunable Sr3Y(BO3)3:Tb3+,Eu3+ phosphors
Journal of Alloys and Compounds 805 (2019) 12e18
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Luminescent properties and energy transfer in novel single-phase multicolor tunable Sr3Y(BO3)3:Tb3þ,Eu3þ phosphors Xiulan Wu, Jinle Zheng*, Qiang Ren, Jianfeng Zhu, Yuhan Ren, Ou Hai** School of Materials Science and Engineering, Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, Shaanxi University of Science and Technology, Xi'an, 710021, People's Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 April 2019 Received in revised form 6 July 2019 Accepted 6 July 2019 Available online 8 July 2019
A novel multicolor tunable phosphors Sr3Y(BO3)3:xTb3þ,yEu3þ (SYBO:xTb3þ,yEu3þ) had been obtained by conventional solid state reaction. The XRD patterns, scanning electron microscope (SEM) and the luminescence spectral were used to explore the phase composition and crystal structure, luminescence properties as well as the energy transfer and fluorescence lifetimes in detail. Under 376 nm wavelength excitation, the phosphors included green and red color derived from the representative emission wavelengths of the Tb3þ and Eu3þ, respectively. Both the luminescence spectral and the fluorescence lifetimes demonstrated energy transfer in the SYBO:xTb3þ,yEu3þ phosphors. When the doped Eu3þ concentration was 0.5 mol, the energy transfer efficiency was as high as 96.48% and 98.34%, respectively. Moreover, the energy transfer mechanism from Tb3þ to Eu3þ in the SYBO:xTb3þ,yEu3þ phosphors was proved to be the dipoleedipole interaction. With the increase of the Eu3þ concentration, the color of the SYBO:xTb3þ,yEu3þ phosphors could tune from green to light-white, and then to red owing to the existing energy transfer. Those results indicated that the SYBO:xTb3þ,yEu3þ phosphors could be as promising multicolor tunable candidates for WLEDs under UV light. © 2019 Elsevier B.V. All rights reserved.
Keywords: Phosphors Sr3Y(BO3)3:xTb3þ,yEu3þ Fluorescence lifetimes Energy transfer Multicolor tunable
1. Introduction In recent decades, many rare earth ions doped phosphors had been broadly researched and gained applications in many promising fields, such as plasma display panel (PDP) and liquid crystal displays (LCD), even white light diodes (WLEDs) [1e5]. WLEDs served as the fourth generation of illumination energies due to the good brightness, energy saving, long fluorescence lifetime and environmental friendliness [6e9]. Presently, the commercial WLEDs were combined blue-emitting InGaN chip with yellow phosphors [10e12]. However, the approach had low color rendering index and high correlated color temperature (CCT) owing to the insufficient in red section [13e15]. A new approach that used ultraviolet (UV) LED chips to combine tricolor phosphors could overcome the shortcomings of the former [16,17]. Therefore, a single-phased multicolor tunable phosphor prepared and used for WLEDs was a very essential subject. Tb3þ and Eu3þ doped inorganic phosphors had been extensively
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Zheng), [email protected] (O. Hai). https://doi.org/10.1016/j.jallcom.2019.07.061 0925-8388/© 2019 Elsevier B.V. All rights reserved.
researched because of better fluorescence efficiencies and more ideal emission colors when excited by UV light [18,19]. In recent researches such as Mg3In4P6O24:Tb3þ,Eu3þ [20], Sr3La(PO4)3:Tb3þ,Eu3þ [21], Y3Al2Ga3O12:Tb3þ,Eu3þ [22], K2Ln(PO4)(WO4):Tb3þ,Eu3þ [23], the sensitizer Tb3þ improved the emission strength of Eu3þ as well as broadened the absorption range [24e27]. In addition, after extensive literature reviewing, a series of rare earth doped Sr3Y(BO3)3 (SYBO) phosphors were studied, such as SYBO:Dy3þ [28], SYBO:Ce3þ [29], (Sr,Ba)3(Y,La)(BO3)3:Ce3þ [30], SYBO:Er3þ [31], SYBO:Tm3þ [32]. All researches exhibited that SYBO was one of the most desirable rare earth luminescent phosphors due to its lower synthesis temperature, stable physicochemical properties and excellent optical properties of rare earth ions doped phosphors. In this paper, we prepared the multicolor tunable SYBO:xTb3þ,yEu3þ phosphors by conventional solid state reaction. The effective energy transfer in the SYBO:xTb3þ,yEu3þ phosphors were systematically determined by the fluorescence spectra and the fluorescence lifetime. As well, the multicolor phosphors could tune by adjusting the Eu3þ concentration. All showed that the SYBO:xTb3þ,yEu3þ multicolor phosphors were promising application materials for synthesizing UV LEDs.
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
13
2. Experiment
3. Results and discussion
A series of SYBO:xTb3þ,yEu3þ phosphors were prepared by a conventional solid state method. The Y2O3, Tb4O7, Eu2O3 (rare earth oxides) of spectrographically pure (99.99%) and SrCO3, H3BO3 of analytical reagent grade were invoked as the starting materials and weighted accordingly to the stoichiometric ratio. The company of Sinopharm Chemical Reagent Co., Ltd. provided all chemical reagents. Then, the starting materials were ground by grinding 30 min in the agate mortar and placed it in a corundum crucible. This powder mixtures controlled to be 10 C/min rate until 1250 C and calcined in the air for 5 h. Lastly, the phosphors were cooled to the room temperature and reground in the powder form. The phase structure of SYBO:xTb3þ,yEu3þ phosphors were recorded by XRD (Cu ka radiation, l ¼ 0.15406 nm, D/Max-2200, Rigaku, Japan). The morphology structure of the samples was observed by the scanning electron microscope (SEM) (FEI Verios 460, American). The luminescence spectra of the samples were investigated by Hitachi F-4600 fluorescence spectrophotometer (150 W Xe lamp was the light source). In addition, the fluorescence lifetimes curves were researched by Edinburgh Instruments FS5 spectrofluorimeter (150 W Xe lamp was the excitation source). Above researched processes were investigated at room temperature.
Fig. 1(a) presented the XRD images of SYBO, SYBO:0.15 Tb3þ, SYBO:0.2Eu3þ, SYBO:0.15 Tb3þ,0.2Eu3þ samples and the standard data PDF#50e0098 of Ba3Dy(BO3)3. In fact, there wasn't the standard card of SYBO in the existing database, however we found a standard card of the isostructural structure compound Ba3Dy(BO3)3 [33,34]. All diffraction peaks of the SYBO host material was slightly shifted to higher diffraction angles similarly when compared with the Ba3Dy(BO3)3 standard card because of the effective ionic radii value of Sr was smaller than Ba, Y and Dy are very close (Some effective ionic radiuses were showed in Table 1). Therefore, the prepared sample was the SYBO pure phase. All the XRD images of the Tb3þ and Eu3þ doped phosphors accorded well with the SYBO indicating that Tb3þ, Eu3þ singly doped or Tb3þ/Eu3þ co-doped did not appear any impurities or significant changes in the SYBO host material. Fig. 1(b) showed the SYBO structure position and the coordination sites of the Sr2þ and Y3þ ions. According to the previous Wyckoff position reports [30], Sr2þ occupied 18f, it's
Table 1 The effective ionic radius (Å) of Sr3Y(BO3)3 host material and other ions. Site
CN
Sr2þ
Y3þ
Tb3þ
Ce3þ
Ba2þ
Dy3þ
18f 3a/3b
8 6
1.26 e
e 0.9
1.04 0.923
1.143 1.01
1.42 e
e 0.91
Fig. 1. (a) XRD images for the as-prepared phosphors of SYBO, SYBO:0.15 Tb3þ, SYBO:0.2Eu3þ, SYBO:0.15 Tb3þ,0.2Eu3þ and the standard data of Ba3Dy(BO3)3 (PDF#50e0098) as a reference. (b) Crystal structure of Sr3Y(BO3)3 and the coordination sites of the Sr2þ and Y3þ ions. (c) SEM and (d) EDS images of the SYBO:0.15 Tb3þ,0.2Eu3þ phosphor.
14
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
coordination number (CN) was 8; Y3þ occupied the two sites of 3a and 3b, it's coordination number was 6. Table 1 showed the effective ionic radius of SYBO host material and other ions. Take into account of the ionic radius and the valence state of the Tb3þ and Eu3þ ions with the host material cations Sr2þ and Y3þ, which manifested that Tb3þ and Eu3þ would substitute for the Y3þ ion. Fig. 1(c) and (d) showed SEM and the energy dispersive spectrometer (EDS) patterns of SYBO:0.15 Tb3þ,0.2Eu3þ phosphor, respectively. SEM presented that the phosphor showed inhomogeneity morphology and consisted of many 5e10 mm particles, which were best to get a good luminescence property. EDS proved that the phosphor was consisted of the Sr, Y, B, O host elements and the Tb, Eu rare elements. The phosphor proportion was Sr: Y: B: O ¼ 7.87: 3.32 : 9.04:77.84 z 3 : 1: 3 : 9. The result was basically accorded with the theoretical proportion of SYBO except for the doped rare earth elements Tb and Eu, which was slight error. Combined the EDS and XRD in Fig. 1(a) for further demonstrated that the prepared phosphors were the pure phase, which was beneficial to analysis the luminescence spectral and energy transfer mechanism. Fig. 2 exhibited the excitation and emission spectra of the different rare ions doped phosphors SYBO:0.15 Tb3þ and SYBO:0.2Eu3þ, and co-doped sample SYBO:0.05 Tb3þ,0.03Eu3þ. In Fig. 2(a), the excitation spectrum of SYBO:0.05 Tb3þ monitored at 547 nm had a broaden absorption from 325 nm to 400 nm. Two stronger peaks located at 352 nm and 376 nm, which were ascribed to the 4f8-4f75d transition spin-forbidden of Tb3þ ions. Under 376 nm wavelength excitation, the main peaks located at 490 nm, 547 nm, 585 nm, and 625 nm were ascribed to the transitions 5 D4/7FJ (J ¼ 6, 5, 4, 3) of the doped Tb3þ ions. According to the magnetic dipole transition rule and Laporte's forbidden transition, the phosphors displayed bright green [35]. Fig. 2(b) presented the excitation and emission spectra of SYBO:0.2Eu3þ phosphors. The excitation spectra monitored at 614 nm showed classes of sharp peaks covering from 325 nm to 550 nm. And these sharp peaks located in the wavelengths of 361 nm, 382 nm, 393 nm, 466 nm and 534 nm, which attribute to 7F0/5D4, 3G5, 5L6, 5D2, 5D1 characteristic transitions of Eu3þ ions, respectively. Upon the excitation wavelength at 393 nm, the emission spectrum depicted two strong
Fig. 2. The excitation and emission spectra of (a) SYBO:0.15 Tb3þ, (b)SYBO:0.2Eu3þ, and (c) SYBO:0.15 Tb3þ,0.2Eu3þ phosphors.
peaks at 594 nm and 614 nm and two weak peaks at 655 nm and 707 nm, which derived from the transition 5D0-7FJ (J ¼ 1, 2, 3, 4) of the doped Eu3þ. In order to verify that the adding sensitizer Tb3þ could increase the absorption intensity of the activator Eu3þ emission spectrum. There was a partial overlap region between the emission spectrum of SYBO:0.15 Tb3þ and the excitation spectrum of SYBO:0.2Eu3þ. According to the Dexter's theory indicated that energy transfer existed in the SYBO:xTb3þ,yEu3þ phosphors [36]. This conclusion could be further affirmed by the spectra of the SYBO:0.15 Tb3þ,0.2Eu3þ phosphors in Fig. 2(c). Under detecting at 547 nm and 614 nm, two excitation spectra included the character bands of the SYBO:0.15 Tb3þ and SYBO:0.2Eu3þ phosphors. Moreover, under the wavelength of 376 nm excitation, the emission spectra had the main character peaks of Tb3þ (576 nm) and Eu3þ (614 nm). This phenomenon showed that the SYBO:xTb3þ,yEu3þ phosphors might exist energy transfer and could be served as UV excitation multicolor tunable emitting phosphors in WLEDs. Fig. 3 exhibited the emission spectra of SYBO:xTb3þ at different concentration under 376 nm excitation and inset visually showed the main peak 547 nm emission intensity of the Tb3þ as a function of the Tb3þ concentration. As the Tb3þ concentration increased, the Tb3þ relative emission intensity increased firstly and then decreased; when x ¼ 0.15 mol, the intensity reached to maximum value, which was caused the concentration quenching effect. The effect could be well clarified by the critical distance (Rc) between Tb3þ-Tb3þ, which could be estimated by formula (1) [27,37]:
1=3 3V Rc ¼ 2 4pXcN
(1)
where V was the volume of unit cell, Xc was the critical concentration of Tb3þ. N was the number of sites that could be substituted by Tb3þ. In SYBO material, V ¼ 1253.693 Å3 [30], Xc ¼ 0.15 mol, N ¼ 6. After calculating, the Rc of SYBO:xTb3þ was 13.856 Å. Fig. 4(a) demonstrated the emission spectra of the SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) phosphors at 376 nm wavelength excitation. The emission spectra contained the characteristic sharp bands of Tb3þ and Eu3þ.With increasing of the Eu3þ concentration, the Eu3þ relative intensity of that at 614 nm increased, while Tb3þ at 547 nm decreased simultaneously, manifesting that energy transfer might exist in the
Fig. 3. The emission spectra of phosphors SYBO: xTb3þ (y ¼ 0.01, 0.04, 0.07, 0.1, 0.15, 0.2, 0.3) and inset show the relative emission strength at 547 nm.
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
15
Fig. 4. (a) The emission spectra of phosphors SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) excited at wavelength of 376 nm. (b)The energy transfer efficiency from Tb3þ to Eu3þ, emission intensity of Tb3þ ions at 547 nm and Eu3þ ions at 614 nm in SYBO:0.15 Tb3þ,yEu3þ phosphors.
SYBO:0.15 Tb3þ,yEu3þ phosphors. In addition, the energy transfer (hET) efficiency from the sensitizer Tb3þ to the activator Eu3þ ions in SYBO:xTb3þ,yEu3þ phosphors, which could be estimated by formula (2) [37,38]:
hET ¼ 1
I I0
(2)
where I0 and I were the emission intensities of Tb3þ ion without and with Eu3þ ion. Fig. 4(b) depicted the variations of Tb3þ and Eu3þ emission intensities, as well as the hET values of Tb3þ-Eu3þ in SYBO:0.15 Tb3þ, yTb3þ phosphors. The Tb3þ emission intensity reduced, while the Eu3þ and the hET efficiency increased with the increasing of Eu3þ. In addition, the hET efficiency maximum reached to 96.48% when the doped Eu3þ was 0.5 mol. Moreover, there was an effective energy transfer inSYBO:xTb3þ,yEu3þ phosphors, which could also be demonstrated by the subsequent fluorescence lifetimes. The fluorescence lifetimes of phosphors not only were used as an important performance indicator in the preparation of white LEDs but also could prove the existence of energy transfer. Fig. 5
showed the fluorescence decay curves of Tb3þ emission in SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.1, 0.2, 0.3 and 0.5). The fluorescence decay curves are fitted with double-exponential using formula (3), as well the fluorescence lifetimes (t) of the phosphors can be estimated by formula (4) [39,40]:
t t þ A2 exp It ¼ A1 exp
t1
t ¼ A1 t21 þ A2 t22
(3)
t2
. ðA1 t1 þ A2 t2 Þ
(4)
where It was the instant emission intensity, t was time, A1 and A2 were constants, t1 and t2 were the rapid and slow lifetimes, respectively. Table 2 listed the fitting values of A1, A2, t1, t2 and t of the fluorescence lifetime curves. The average lifetimes decreased from 2.904 ms to 0.057 ms with the Eu3þ increased from 0 mol to 0.5 mol in SYBO:0.15 Tb3þ,yEu3þ phosphors. In addition, the fluorescence lifetimes energy transfer (hT) efficiency could also be estimated by formula (5) [41]:
hT ¼ 1
tS tS0
(5)
where ts0 and ts were the fluorescence lifetimes of the Tb3þ without and with the Eu3þ, respectively. The fluorescence lifetimes hT efficiency were also listed in Table 2. The hT efficiency increased with the increasing of the Eu3þconcentration and the highest was 98.34% when the doped content of the Eu3þ ions was 0.5 mol. All results strongly demonstrated that the energy transfer existed in SYBO:xTb3þ,yEu3þ and the fluorescence lifetimes were enough to apply to the promoting of WLEDs. The energy transfer in SYBO:xTb3þ, yEu3þ phosphors included the exchange interaction electric multipolar interaction mechanism. It could be analyzed by the combined formula (6) of Dexter's
Table 2 The fitting parameters value and average lifetime of Tb3þ in SYBO:0.15 Tb3þ, yEu3þ.
Fig. 5. The decay curves of Tb3þ ions in SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.1, 0.2, 0.3 and 0.5) phosphors (excited at 376 nm and monitored at 547 nm).
y/mol
A1
A2
t1/ms
t2/ms
tav/ms
h/%
0 0.1 0.2 0.3 0.5
208.883 699.44 590.794 671.035 609.763
98.963 39.405 18.139 4.654 0.949
3.8718 7.0633 11.9496 10.4194 10.0855
2912.2022 1878.653 1156.3166 669.9902 580.8526
2.904 1.762 0.868 0.214 0.057
e 39.33 70.11 90.63 98.34
16
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
energy transfer and Reisfeld's approximation formula [42e44]:
I0 fC n=3 I
(6)
In formula (6), C was the sum concentration of the doped ions and n was a parameter. Fig. 6 showed the relationships I0/I-C and I0/ I-Cn/3 (n ¼ 6, 8, 10). The relationships between I0/I-C and n ¼ 6, 8, and 10 were corresponding to the exchange interaction, the dipoledipole, the dipole-quadrupole and the quadrupole-quadrupole interaction, respectively. Obviously, the fitting parameter R2 was best only when n ¼ 6, implying that the electric dipoleedipole interaction was the main energy transfer mechanism in SYBO:xTb3þ,yEu3þ phosphors. Fig. 7 depicted the CIE chromaticity coordinate positions and the digital photographs of the SYBO:xTb3þ,yEu3þ phosphors under the wavelength of 376 nm excitation. Table 3 listed the CIE chromaticity coordinate as well as the CCT [45] values of the SYBO:0.15 Tb3þ,yTb3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) and SYBO:0.2Eu3þ phosphors. The CCT could be estimated by the following formula (7) [37]:
CCT ¼ 437n3 þ 601n2 6861n þ 5514:31
(7)
where n ¼ (x-xe)/(y-ye), (xe, ye) was the coordinate of the epicenter and its values was xe ¼ 0.3320, ye ¼ 0.1858. Moreover, the CCT firstly decreased and then increased, and it reached to maximums 1974 K when y ¼ 0.2 mol. With the increasing of Eu3þ, the color of the SYBO:xTb3þ,yEu3þ phosphors could tune from green (0.289, 0.457), light-white (0.373, 0.383) and finally adjust to
red (0.633, 0.365); the CIE tunable range was broader than the Y3Al2Ga3O12:Tb3þ,Eu3þ(from (0.4273, 0.5123) to (0.6193, 0.3801)) [22] and Gd2O2CN2:Tb3þ,Eu3þ (from (0.3134, 0.5454) to (0.5682, 0.3322)) [39] phosphors. SYBO:0.2Eu3þ (0.633, 0.365) was closer the National Television System Committee (NTSC) standard red phosphor (0.67, 0.33) than that two phosphors. The multicolor single-phase emissions phosphors were potentially attracted applications such as photoelectric equipment and liquid crystal displays.
4. Conclusions In conclusion, we had prepared a classes of multicolor tunable SYBO:xTb3þ,yEu3þ phosphors and investigated the luminescence properties. Under 376 nm excitation, SYBO:xTb3þ phosphors appeared intense green light, the critical quenching of the Tb3þ concentration was 0.15 mol and the critical distance between Tb3þTb3þ was 13.856 Å. According to analysis the luminescence spectra and the fluorescence lifetime curves, the energy transfer mechanism from Tb3þ to Eu3þin SYBO:xTb3þ,yEu3þ via dipoleedipole interaction as well as the energy transfer efficiency was as high as 96.48% and 98.34%. As the increase of the Eu3þ concentrations in the SYBO:xTb3þ,yEu3þ phosphors and depending the energy transfer, CIE coordinates could adjust from (0.289, 0.457), (0.373, 0.383) to (0.633, 0.365), which was corresponding to the color from green, light-white finally to red. All results showed that the SYBO:xTb3þ,yEu3þ phosphors could act as UV light excited multicolor tunable materials for WLEDs.
Fig. 6. The dependence of Is0/Is of Tb3þ on (a) C(Tb3þþEu3þ), (b) C(Tb3þþEu3þ)6/3, (c) C(Tb3þþEu3þ)8/3 and (d) C(Tb3þþEu3þ)10/3.
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11] Fig. 7. The CIE chromaticity coordinate positions and the digital photographs of the SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) and SYBO:0.2Eu3þ phosphors.
[12]
[13] Table 3 The CIE chromaticity coordinate and CCT values of SYBO:xTb3þ,yEu3þphosphors. Sample
CIE coordinates (x, y)
CCT (K)
SYBO:0.15 Tb3þ SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.2Eu3þ
(0.289, (0.316, (0.373, (0.427, (0.484. (0.513, (0.539, (0.633,
6773 6016 4232 2607 1974 2625 3632 5228
0.01Eu3þ 0.05Eu3þ 0.1Eu3þ 0.2Eu3þ 0.3Eu3þ 0.5Eu3þ
0.457) 0.445) 0.383) 0.355) 0.332) 0.322) 0.324) 0.365)
[14]
[15]
[16]
[17]
Acknowledgement
[18]
This work was financially supported by the Innovation of Science and Technology Plan Projects of Shaanxi Province, China (Grant No. 2013KTDZ03-02-01, 2017TSCXL-GY-07-02), Scientific Research Program Funded by Shaanxi Provincial Education Department (Program No. 18JK0115), Research Starting Foundation from Shaanxi University of Science and Technology (Grant no.2016BJ-41), and the Graduate Innovation Fund of Shaanxi University of Science and Technology (Grant no. SUST-A04).
[21]
Appendix A. Supplementary data
[22]
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.07.061.
[23]
[19]
[20]
References [24] [1] C. Ji, Z. Huang, X. Tian, W. Xie, J. Wen, H. He, C. Zhou, T. Zeng, Synthesis and
17
photoluminescence properties of a novel BaGe4O9:Eu3þ red emitting phosphor for warm white LEDs, Dyes Pigments 160 (2019) 772e778, https:// doi.org/10.1016/j.dyepig.2018.09.012. Z. Wang, F. Yuan, X. Li, Y. Li, H. Zhong, L. Fan, 53% Efficient Red Emissive Carbon Quantum Dots for High Color Rendering and Stable Warm WhiteLight-Emitting Diodes, 2017, pp. 1e7, https://doi.org/10.1002/ adma.201702910, 1702910. S.J. Park, B.S. Je, J.W. Jang, M.S. Oh, M.S. Koo, S.J. Yang, H.K. Yang, Green and red emitting YBO3:Ln3þ (Ln ¼ Eu, Tb) phosphors for detection of latent fingerprint, J. Alloy. Comp. 789 (2019) 367e374, https://doi.org/10.1016/ j.jallcom.2019.03.029. S. Liao, W. Zhang, J. Zhang, Site-sensitive energy transfer from Ce3þ to Tb3þ/ Mn2þ based on an efficient phosphor Li4SrCa(SiO4)2:Ce3þ, Ceram. Int. 44 (2018) 18413e18419, https://doi.org/10.1016/j.ceramint.2018.07.058. W. Zhang, H. Shen, X. li Hu, Y. Wang, J. fu Li, Z. jie Zhu, Z. yu You, C. yang Tu, Solid-state synthesis, structure and spectroscopic analysis of Dy:CaYAl3O7 phosphors, J. Alloy. Comp. 781 (2019) 255e260, https://doi.org/10.1016/ j.jallcom.2018.12.113. S. Zhu, X. Zhang, W. Li, M. Liu, L. Cheng, X. Mi, L. Lu, Phase transformation and luminescence properties of Y2.94Al5-xGaxO12:0.06Ce3þ phosphors, Ceram. Int. 45 (2018) 4964e4971, https://doi.org/10.1016/j.ceramint.2018.11.196. D.K. Singh, J. Manam, Efficient dual emission mode of green emitting perovskite BaTiO3: Er3þ phosphors for display and temperature sensing applications, Ceram. Int. 44 (2018) 10912e10920, https://doi.org/10.1016/ j.ceramint.2018.03.151. D.A. Hakeem, D.H. Kim, S.W. Kim, K. Park, Crystal structure and photoluminescence properties of novel garnet Y2-xLaCaGa3ZrO12:xLn3þ (Ln ¼ Eu and Tb) phosphors, Dyes Pigments 163 (2019) 715e724, https://doi.org/ 10.1016/j.dyepig.2018.12.045. Z. Leng, H. Xiong, L. Li, N. Zhang, Y. Liu, S. Gan, Facile controlled synthesis different morphologies of LuBO3:Ln3þ (Ln ¼ Eu, Tb) phosphors and tunable luminescent properties, J. Alloy. Comp. 646 (2015) 632e638, https://doi.org/ 10.1016/j.jallcom.2015.06.162. X. Huang, H. Guo, LiCa3MgV3O12:Sm3þ: a new high-efficiency white-emitting phosphor, Ceram. Int. 44 (2018) 10340e10344, https://doi.org/10.1016/ j.ceramint.2018.03.043. Q. Cheng, F. Ren, Q. Lin, H. Tong, X. Miao, High quantum efficiency red emitting a-phase La2W2O9:Eu3þ phosphor, J. Alloy. Comp. 772 (2018) 905e911, https://doi.org/10.1016/j.jallcom.2018.08.320. C. La, S. Po, Luminescence property and energy transfer behavior of apatitetype, Mater. Res. Bull. 108 (2018) 101e105, https://doi.org/10.1016/ j.materresbull.2018.08.040. X. Huang, H. Guo, A novel highly efficient single-composition tunable whitelight-emitting LiCa3MgV3O12:Eu3þ phosphor, Dyes Pigments 154 (2018) 82e86, https://doi.org/10.1016/j.dyepig.2018.02.047. J. Zhou, Z. Xia, Multi-color emission evolution and energy transfer behavior of La3GaGe5O16:Tb3þ,Eu3þ phosphors, Mater. Chem. C (2014) 2, https://doi.org/ 10.1039/C4TC01091D. X. Wu, Y. Jiao, O. Hai, Q. Ren, F. Lin, H. Li, Effect of single and composite fluxes on the morphology and luminescence properties of layered perovskite Sr1.95TiO4:0.05Sm3þ phosphor, J. Lumin. 192 (2017) 626e633, https://doi.org/ 10.1016/j.jlumin.2017.07.054. L. Li, X. Tang, Z. Wu, Y. Zheng, S. Jiang, X. Tang, G. Xiang, X. Zhou, Simultaneously tuning emission color and realizing optical thermometry via efficient Tb3þ/Eu3þ energy transfer in whitlockite-type phosphate multifunctional phosphors, J. Alloy. Comp. 780 (2019) 266e275, https://doi.org/10.1016/ j.jallcom.2018.11.378. W. Ma, J. Zhang, X. Zhang, X. Zhang, Y. Liu, S. Liao, S. Lian, Highly efficient and thermal stable La2Si2O7:Ce3þ,Tb3þ,Eu3þ phosphors: emission color tuning through terbium bridge, J. Alloy. Comp. 785 (2019) 53e61, https://doi.org/ 10.1016/j.jallcom.2019.01.194. T. Dogan, L. Tormo, S. Akca, N. Kucuk, J.G. Guinea, Y. Karabulut, M. Ayvacikli, M. Oglakci, M. Topaksu, N. Can, Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3þ phosphors prepared via wet-chemical synthesis, Ceram. Int. 45 (2019) 4918e4925, https://doi.org/10.1016/j.ceramint.2018.11.191. D. Zhang, G. Li, W. Yang, W. Huang, Z. Leng, S. Fang, L. Li, Tunable photoluminescence properties and energy transfer of Ca5(BO3)3F:Tb3þ/Eu3þ phosphors for solid state lighting, J. Lumin. 208 (2019) 155e163, https://doi.org/ 10.1016/j.jlumin.2018.12.022. J. Zhang, G.M. Cai, G.X. Zhang, Z.P. Jin, Insight into crystal structure and Eu/Tb doped luminescence property of a new phosphate, J. Alloy. Comp. 762 (2018) 444e455, https://doi.org/10.1016/j.jallcom.2018.05.079. X. Zhang, J. Zhang, Y. Chen, M. Gong, Energy transfer and multicolor tunable emission in single-phase Tb3þ, Eu3þ co-doped Sr3La(PO4)3 phosphors, Ceram. Int. 42 (2016) 13919e13924, https://doi.org/10.1016/j.ceramint.2016.05.202. Z. Li, B. Zhong, Y. Cao, S. Zhang, Y. Lv, Z. Mu, Z. Hu, Y. Hu, Energy transfer and tunable luminescence properties in Y3Al2Ga3O12:Tb3þ,Eu3þ phosphors, J. Alloy. Comp. 787 (2019) 672e682, https://doi.org/10.1016/ j.jallcom.2019.02.154. D. Wen, J. Feng, J. Li, J. Shi, M. Wu, Q. Su, K2Ln(PO4)(WO4):Tb3þ,Eu3þ (Ln ¼ Y, Gd and Lu) phosphors: highly efficient pure red and tuneable emission for white light-emitting diodes, J. Mater. Chem. C. 3 (2015) 2107e2114, https:// doi.org/10.1039/c4tc02406k. J.Y. Si, N. Liu, S.Y. Song, G.M. Cai, N. Yang, Z. Li, Investigation on Eu/Tb activated photoluminescent properties of Li3Sc(BO3)2 based phosphors, J. Alloy. Comp.
18
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
719 (2017) 171e181, https://doi.org/10.1016/j.jallcom.2017.05.161. [25] Z. Chen, X. Chen, S. Huang, Y. Pan, A novel tunable green-to-red emitting phosphor Ca4Lao(BO3)3:Tb,Eu via energy transfer with high quantum yield, Ceram. Int. 42 (2016) 13476e13484, https://doi.org/10.1016/ j.ceramint.2016.05.139. [26] Y. Zhang, X. Zhang, H. Zhang, Z.-C. Wu, Y. Liu, L. Ma, X. Wang, W.-R. Liu, B. Lei, Enhanced absorption of Sr3Lu2(BO3)4:Ce3þ,Tb3þ phosphor with energy transfer for UV-pumped white LEDs, J. Alloy. Comp. 789 (2019) 215e220, https://doi.org/10.1016/j.jallcom.2019.03.088. [27] X. Wu, J. Zheng, Q. Ren, W. Bai, Y. Ren, O. Hai, Synthesis and luminescent properties of a novel orange-red Ba3Y(BO3)3:Sm3þ phosphors for white LEDs, Polyhedron 164 (2019) 17e22, https://doi.org/10.1016/j.poly.2019.02.031. [28] T. Jiang, Y. Chen, X. Gong, Y. Lin, J. Huang, Z. Luo, Y. Huang, Spectroscopic Properties of Dy3þ-Doped Sr3Y(BO3)3 Crystal, vol 91, 2019, pp. 171e176, https://doi.org/10.1016/j.optmat.2019.03.004. [29] R. Simura, S. Kawai, K. Sugiyama, T. Yanagida, T. Sugawara, T. Shishido, A. Yoshikawa, Valence state of dopant and scintillation properties of Ce-doped Sr3Y(BO3)3 crystal, J. Cryst. Growth 362 (2013) 296e299, https://doi.org/ 10.1016/j.jcrysgro.2011.11.089. [30] K.A. Denault, Z. Cheng, J. Brgoch, S.P. Denbaars, R. Seshadri, Structurecomposition relationships and optical properties in cerium-substituted (Sr,Ba)3(Y,La)(BO3)3 borate phosphors, J. Mater. Chem. C. 1 (2013) 7339e7345, https://doi.org/10.1039/c3tc31621a. [31] D. Zhao, G. Wang, Growth and Spectroscopic Characterization of Er3þ : Sr3Y(BO3)3 Crystal, vol 130, 2010, pp. 424e428, https://doi.org/10.1016/ j.jlumin.2009.10.007. [32] X. Meng, L. Zhang, G. Wang, Growth and Spectral Properties of Tm3þ-Doped Sr3Y(BO3)3 Crystal, vol 481, 2009, pp. 354e357, https://doi.org/10.1016/ j.jallcom.2009.02.136. [33] H. Xu, Z. Xia, H. Liu, L. Liao, Luminescence properties and energy transfer in La5-x-ySi2BO13:xCe3þ, yTb3þ phosphor, ECS J. Solid State Sci. Technol. 2 (2013) R186eR189, https://doi.org/10.1149/2.035309jss. [34] X. Wu, Y. Jiao, Q. Ren, O. Hai, F. Lin, H. Li, W. Bai, Photoluminescence and energy transfer in Sr3La(BO3)3:Ce, Sm and Sr2TiO4:Sm, Eu phosphors, Optic Laser. Technol. 108 (2018) 456e465, https://doi.org/10.1016/ j.optlastec.2018.07.043. [35] B. Li, X. Huang, H. Guo, Y. Zeng, Energy transfer and tunable photoluminescence of LaBWO6:Tb3þ,Eu3þ phosphors for near-UV white LEDs, Dyes
Pigments 150 (2018) 67e72, https://doi.org/10.1016/j.dyepig.2017.11.003. [36] M. Chen, Z. Xia, Q. Liu, Luminescence properties and energy transfer of Ce3þ/ Tb3þ co-doped Ca6Ba(PO4)4O phosphor for near-UV pumped light-emitting diodes, J. Mater. Chem. C. 3 (2015) 4197e4204, https://doi.org/10.1039/ c5tc00358j. [37] X. Wu, W. Bai, O. Hai, Q. Ren, F. Lin, Y. Jiao, Structure, luminescence properties and energy transfer of Dy3þ and Eu3þ codoped KBa(VO4) phosphor, J. Solid State Chem. 265 (2018) 109e116, https://doi.org/10.1016/j.jssc.2018.05.033. [38] Y. Fang, X. Tian, J. Liu, Y. Zhang, Y. Liu, G. Zhao, J. Zou, N. Vainos, J. Hou, Trichromatic emission from a single-phase Na5Y4(SiO4)4F:Eu2þ,Tb3þ,Eu3þ phosphor for white-light-emitting diodes, J. Lumin. 207 (2018) 34e40, https:// doi.org/10.1016/j.jlumin.2018.10.010. , F. Tessier, G. Chen, Novel color-tunable [39] S. Yuan, L. Wang, Y. Yang, F. Chevire Gd2O2CN2:Tb3þ,Eu3þ phosphors: characterization and photoluminescence properties, Ceram. Int. 42 (2016) 12508e12511, https://doi.org/10.1016/ j.ceramint.2016.04.059. [40] Q. Ren, F. Lin, X. Wu, O. Hai, T. Wei, Y. Jiao, H. Li, Synthesis and luminescent properties of KGd(MoO4)2:Sm3þ red phosphor for white light emitting diodes, Mater. Res. Bull. 90 (2017) 66e72, https://doi.org/10.1016/ j.materresbull.2017.02.023. [41] H. Lai, J. Zhang, D. Hou, H. Guan, X. Ye, Luminescence characteristics and energy transfer of Eu2þ/Tb3þ doped single phase multi-color phosphor, Ceram. Int. 44 (2018) 15072e15078, https://doi.org/10.1016/ j.ceramint.2018.05.140. [42] Z. Xia, Y. Liang, D. Yu, M. Zhang, W. Huang, M. Tong, J. Wu, J. Zhao, Photoluminescence properties and energy transfer in color tunable BaY2Si3O10: Ce,Tb phosphors, Optic Laser. Technol. 56 (2014) 387e392, https://doi.org/ 10.1016/j.optlastec.2013.09.014. [43] M. Jiao, Y. Jia, W. Lü, W. Lv, Q. Zhao, B. Shao, H. You, Sr3GdNa(PO4)3F: Eu2þ,Mn2þ: a potential color tunable phosphor for white LEDs, J. Mater. Chem. C. 2 (2014) 90e97, https://doi.org/10.1039/c3tc31837k. [44] X. Wu, Y. Jiao, O. Hai, Q. Ren, F. Lin, H. Li, Photoluminescence, energy transfer, color tunable properties of Sr3La(BO3)3:Ce, Tb phosphors, J. Alloy. Comp. 730 (2018) 521e527, https://doi.org/10.1016/j.jallcom.2017.10.022. [45] H. Xiong, Y. Zhang, Y. Liu, T. Gao, L. Zhang, Z.A. Qiao, L. Zhang, S. Gan, Q. Huo, Self-template construction of honeycomb-like mesoporous YPO4:Ln3þ (Ln ¼ Eu, Tb) phosphors with tuneable luminescent properties, J. Alloy. Comp. 782 (2019) 845e851, https://doi.org/10.1016/j.jallcom.2018.12.107.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Luminescent properties and energy transfer in novel single-phase multicolor tunable Sr3Y(BO3)3:Tb3þ,Eu3þ phosphors Xiulan Wu, Jinle Zheng*, Qiang Ren, Jianfeng Zhu, Yuhan Ren, Ou Hai** School of Materials Science and Engineering, Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials, Shaanxi University of Science and Technology, Xi'an, 710021, People's Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 April 2019 Received in revised form 6 July 2019 Accepted 6 July 2019 Available online 8 July 2019
A novel multicolor tunable phosphors Sr3Y(BO3)3:xTb3þ,yEu3þ (SYBO:xTb3þ,yEu3þ) had been obtained by conventional solid state reaction. The XRD patterns, scanning electron microscope (SEM) and the luminescence spectral were used to explore the phase composition and crystal structure, luminescence properties as well as the energy transfer and fluorescence lifetimes in detail. Under 376 nm wavelength excitation, the phosphors included green and red color derived from the representative emission wavelengths of the Tb3þ and Eu3þ, respectively. Both the luminescence spectral and the fluorescence lifetimes demonstrated energy transfer in the SYBO:xTb3þ,yEu3þ phosphors. When the doped Eu3þ concentration was 0.5 mol, the energy transfer efficiency was as high as 96.48% and 98.34%, respectively. Moreover, the energy transfer mechanism from Tb3þ to Eu3þ in the SYBO:xTb3þ,yEu3þ phosphors was proved to be the dipoleedipole interaction. With the increase of the Eu3þ concentration, the color of the SYBO:xTb3þ,yEu3þ phosphors could tune from green to light-white, and then to red owing to the existing energy transfer. Those results indicated that the SYBO:xTb3þ,yEu3þ phosphors could be as promising multicolor tunable candidates for WLEDs under UV light. © 2019 Elsevier B.V. All rights reserved.
Keywords: Phosphors Sr3Y(BO3)3:xTb3þ,yEu3þ Fluorescence lifetimes Energy transfer Multicolor tunable
1. Introduction In recent decades, many rare earth ions doped phosphors had been broadly researched and gained applications in many promising fields, such as plasma display panel (PDP) and liquid crystal displays (LCD), even white light diodes (WLEDs) [1e5]. WLEDs served as the fourth generation of illumination energies due to the good brightness, energy saving, long fluorescence lifetime and environmental friendliness [6e9]. Presently, the commercial WLEDs were combined blue-emitting InGaN chip with yellow phosphors [10e12]. However, the approach had low color rendering index and high correlated color temperature (CCT) owing to the insufficient in red section [13e15]. A new approach that used ultraviolet (UV) LED chips to combine tricolor phosphors could overcome the shortcomings of the former [16,17]. Therefore, a single-phased multicolor tunable phosphor prepared and used for WLEDs was a very essential subject. Tb3þ and Eu3þ doped inorganic phosphors had been extensively
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (J. Zheng), [email protected] (O. Hai). https://doi.org/10.1016/j.jallcom.2019.07.061 0925-8388/© 2019 Elsevier B.V. All rights reserved.
researched because of better fluorescence efficiencies and more ideal emission colors when excited by UV light [18,19]. In recent researches such as Mg3In4P6O24:Tb3þ,Eu3þ [20], Sr3La(PO4)3:Tb3þ,Eu3þ [21], Y3Al2Ga3O12:Tb3þ,Eu3þ [22], K2Ln(PO4)(WO4):Tb3þ,Eu3þ [23], the sensitizer Tb3þ improved the emission strength of Eu3þ as well as broadened the absorption range [24e27]. In addition, after extensive literature reviewing, a series of rare earth doped Sr3Y(BO3)3 (SYBO) phosphors were studied, such as SYBO:Dy3þ [28], SYBO:Ce3þ [29], (Sr,Ba)3(Y,La)(BO3)3:Ce3þ [30], SYBO:Er3þ [31], SYBO:Tm3þ [32]. All researches exhibited that SYBO was one of the most desirable rare earth luminescent phosphors due to its lower synthesis temperature, stable physicochemical properties and excellent optical properties of rare earth ions doped phosphors. In this paper, we prepared the multicolor tunable SYBO:xTb3þ,yEu3þ phosphors by conventional solid state reaction. The effective energy transfer in the SYBO:xTb3þ,yEu3þ phosphors were systematically determined by the fluorescence spectra and the fluorescence lifetime. As well, the multicolor phosphors could tune by adjusting the Eu3þ concentration. All showed that the SYBO:xTb3þ,yEu3þ multicolor phosphors were promising application materials for synthesizing UV LEDs.
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
13
2. Experiment
3. Results and discussion
A series of SYBO:xTb3þ,yEu3þ phosphors were prepared by a conventional solid state method. The Y2O3, Tb4O7, Eu2O3 (rare earth oxides) of spectrographically pure (99.99%) and SrCO3, H3BO3 of analytical reagent grade were invoked as the starting materials and weighted accordingly to the stoichiometric ratio. The company of Sinopharm Chemical Reagent Co., Ltd. provided all chemical reagents. Then, the starting materials were ground by grinding 30 min in the agate mortar and placed it in a corundum crucible. This powder mixtures controlled to be 10 C/min rate until 1250 C and calcined in the air for 5 h. Lastly, the phosphors were cooled to the room temperature and reground in the powder form. The phase structure of SYBO:xTb3þ,yEu3þ phosphors were recorded by XRD (Cu ka radiation, l ¼ 0.15406 nm, D/Max-2200, Rigaku, Japan). The morphology structure of the samples was observed by the scanning electron microscope (SEM) (FEI Verios 460, American). The luminescence spectra of the samples were investigated by Hitachi F-4600 fluorescence spectrophotometer (150 W Xe lamp was the light source). In addition, the fluorescence lifetimes curves were researched by Edinburgh Instruments FS5 spectrofluorimeter (150 W Xe lamp was the excitation source). Above researched processes were investigated at room temperature.
Fig. 1(a) presented the XRD images of SYBO, SYBO:0.15 Tb3þ, SYBO:0.2Eu3þ, SYBO:0.15 Tb3þ,0.2Eu3þ samples and the standard data PDF#50e0098 of Ba3Dy(BO3)3. In fact, there wasn't the standard card of SYBO in the existing database, however we found a standard card of the isostructural structure compound Ba3Dy(BO3)3 [33,34]. All diffraction peaks of the SYBO host material was slightly shifted to higher diffraction angles similarly when compared with the Ba3Dy(BO3)3 standard card because of the effective ionic radii value of Sr was smaller than Ba, Y and Dy are very close (Some effective ionic radiuses were showed in Table 1). Therefore, the prepared sample was the SYBO pure phase. All the XRD images of the Tb3þ and Eu3þ doped phosphors accorded well with the SYBO indicating that Tb3þ, Eu3þ singly doped or Tb3þ/Eu3þ co-doped did not appear any impurities or significant changes in the SYBO host material. Fig. 1(b) showed the SYBO structure position and the coordination sites of the Sr2þ and Y3þ ions. According to the previous Wyckoff position reports [30], Sr2þ occupied 18f, it's
Table 1 The effective ionic radius (Å) of Sr3Y(BO3)3 host material and other ions. Site
CN
Sr2þ
Y3þ
Tb3þ
Ce3þ
Ba2þ
Dy3þ
18f 3a/3b
8 6
1.26 e
e 0.9
1.04 0.923
1.143 1.01
1.42 e
e 0.91
Fig. 1. (a) XRD images for the as-prepared phosphors of SYBO, SYBO:0.15 Tb3þ, SYBO:0.2Eu3þ, SYBO:0.15 Tb3þ,0.2Eu3þ and the standard data of Ba3Dy(BO3)3 (PDF#50e0098) as a reference. (b) Crystal structure of Sr3Y(BO3)3 and the coordination sites of the Sr2þ and Y3þ ions. (c) SEM and (d) EDS images of the SYBO:0.15 Tb3þ,0.2Eu3þ phosphor.
14
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
coordination number (CN) was 8; Y3þ occupied the two sites of 3a and 3b, it's coordination number was 6. Table 1 showed the effective ionic radius of SYBO host material and other ions. Take into account of the ionic radius and the valence state of the Tb3þ and Eu3þ ions with the host material cations Sr2þ and Y3þ, which manifested that Tb3þ and Eu3þ would substitute for the Y3þ ion. Fig. 1(c) and (d) showed SEM and the energy dispersive spectrometer (EDS) patterns of SYBO:0.15 Tb3þ,0.2Eu3þ phosphor, respectively. SEM presented that the phosphor showed inhomogeneity morphology and consisted of many 5e10 mm particles, which were best to get a good luminescence property. EDS proved that the phosphor was consisted of the Sr, Y, B, O host elements and the Tb, Eu rare elements. The phosphor proportion was Sr: Y: B: O ¼ 7.87: 3.32 : 9.04:77.84 z 3 : 1: 3 : 9. The result was basically accorded with the theoretical proportion of SYBO except for the doped rare earth elements Tb and Eu, which was slight error. Combined the EDS and XRD in Fig. 1(a) for further demonstrated that the prepared phosphors were the pure phase, which was beneficial to analysis the luminescence spectral and energy transfer mechanism. Fig. 2 exhibited the excitation and emission spectra of the different rare ions doped phosphors SYBO:0.15 Tb3þ and SYBO:0.2Eu3þ, and co-doped sample SYBO:0.05 Tb3þ,0.03Eu3þ. In Fig. 2(a), the excitation spectrum of SYBO:0.05 Tb3þ monitored at 547 nm had a broaden absorption from 325 nm to 400 nm. Two stronger peaks located at 352 nm and 376 nm, which were ascribed to the 4f8-4f75d transition spin-forbidden of Tb3þ ions. Under 376 nm wavelength excitation, the main peaks located at 490 nm, 547 nm, 585 nm, and 625 nm were ascribed to the transitions 5 D4/7FJ (J ¼ 6, 5, 4, 3) of the doped Tb3þ ions. According to the magnetic dipole transition rule and Laporte's forbidden transition, the phosphors displayed bright green [35]. Fig. 2(b) presented the excitation and emission spectra of SYBO:0.2Eu3þ phosphors. The excitation spectra monitored at 614 nm showed classes of sharp peaks covering from 325 nm to 550 nm. And these sharp peaks located in the wavelengths of 361 nm, 382 nm, 393 nm, 466 nm and 534 nm, which attribute to 7F0/5D4, 3G5, 5L6, 5D2, 5D1 characteristic transitions of Eu3þ ions, respectively. Upon the excitation wavelength at 393 nm, the emission spectrum depicted two strong
Fig. 2. The excitation and emission spectra of (a) SYBO:0.15 Tb3þ, (b)SYBO:0.2Eu3þ, and (c) SYBO:0.15 Tb3þ,0.2Eu3þ phosphors.
peaks at 594 nm and 614 nm and two weak peaks at 655 nm and 707 nm, which derived from the transition 5D0-7FJ (J ¼ 1, 2, 3, 4) of the doped Eu3þ. In order to verify that the adding sensitizer Tb3þ could increase the absorption intensity of the activator Eu3þ emission spectrum. There was a partial overlap region between the emission spectrum of SYBO:0.15 Tb3þ and the excitation spectrum of SYBO:0.2Eu3þ. According to the Dexter's theory indicated that energy transfer existed in the SYBO:xTb3þ,yEu3þ phosphors [36]. This conclusion could be further affirmed by the spectra of the SYBO:0.15 Tb3þ,0.2Eu3þ phosphors in Fig. 2(c). Under detecting at 547 nm and 614 nm, two excitation spectra included the character bands of the SYBO:0.15 Tb3þ and SYBO:0.2Eu3þ phosphors. Moreover, under the wavelength of 376 nm excitation, the emission spectra had the main character peaks of Tb3þ (576 nm) and Eu3þ (614 nm). This phenomenon showed that the SYBO:xTb3þ,yEu3þ phosphors might exist energy transfer and could be served as UV excitation multicolor tunable emitting phosphors in WLEDs. Fig. 3 exhibited the emission spectra of SYBO:xTb3þ at different concentration under 376 nm excitation and inset visually showed the main peak 547 nm emission intensity of the Tb3þ as a function of the Tb3þ concentration. As the Tb3þ concentration increased, the Tb3þ relative emission intensity increased firstly and then decreased; when x ¼ 0.15 mol, the intensity reached to maximum value, which was caused the concentration quenching effect. The effect could be well clarified by the critical distance (Rc) between Tb3þ-Tb3þ, which could be estimated by formula (1) [27,37]:
1=3 3V Rc ¼ 2 4pXcN
(1)
where V was the volume of unit cell, Xc was the critical concentration of Tb3þ. N was the number of sites that could be substituted by Tb3þ. In SYBO material, V ¼ 1253.693 Å3 [30], Xc ¼ 0.15 mol, N ¼ 6. After calculating, the Rc of SYBO:xTb3þ was 13.856 Å. Fig. 4(a) demonstrated the emission spectra of the SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) phosphors at 376 nm wavelength excitation. The emission spectra contained the characteristic sharp bands of Tb3þ and Eu3þ.With increasing of the Eu3þ concentration, the Eu3þ relative intensity of that at 614 nm increased, while Tb3þ at 547 nm decreased simultaneously, manifesting that energy transfer might exist in the
Fig. 3. The emission spectra of phosphors SYBO: xTb3þ (y ¼ 0.01, 0.04, 0.07, 0.1, 0.15, 0.2, 0.3) and inset show the relative emission strength at 547 nm.
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
15
Fig. 4. (a) The emission spectra of phosphors SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) excited at wavelength of 376 nm. (b)The energy transfer efficiency from Tb3þ to Eu3þ, emission intensity of Tb3þ ions at 547 nm and Eu3þ ions at 614 nm in SYBO:0.15 Tb3þ,yEu3þ phosphors.
SYBO:0.15 Tb3þ,yEu3þ phosphors. In addition, the energy transfer (hET) efficiency from the sensitizer Tb3þ to the activator Eu3þ ions in SYBO:xTb3þ,yEu3þ phosphors, which could be estimated by formula (2) [37,38]:
hET ¼ 1
I I0
(2)
where I0 and I were the emission intensities of Tb3þ ion without and with Eu3þ ion. Fig. 4(b) depicted the variations of Tb3þ and Eu3þ emission intensities, as well as the hET values of Tb3þ-Eu3þ in SYBO:0.15 Tb3þ, yTb3þ phosphors. The Tb3þ emission intensity reduced, while the Eu3þ and the hET efficiency increased with the increasing of Eu3þ. In addition, the hET efficiency maximum reached to 96.48% when the doped Eu3þ was 0.5 mol. Moreover, there was an effective energy transfer inSYBO:xTb3þ,yEu3þ phosphors, which could also be demonstrated by the subsequent fluorescence lifetimes. The fluorescence lifetimes of phosphors not only were used as an important performance indicator in the preparation of white LEDs but also could prove the existence of energy transfer. Fig. 5
showed the fluorescence decay curves of Tb3þ emission in SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.1, 0.2, 0.3 and 0.5). The fluorescence decay curves are fitted with double-exponential using formula (3), as well the fluorescence lifetimes (t) of the phosphors can be estimated by formula (4) [39,40]:
t t þ A2 exp It ¼ A1 exp
t1
t ¼ A1 t21 þ A2 t22
(3)
t2
. ðA1 t1 þ A2 t2 Þ
(4)
where It was the instant emission intensity, t was time, A1 and A2 were constants, t1 and t2 were the rapid and slow lifetimes, respectively. Table 2 listed the fitting values of A1, A2, t1, t2 and t of the fluorescence lifetime curves. The average lifetimes decreased from 2.904 ms to 0.057 ms with the Eu3þ increased from 0 mol to 0.5 mol in SYBO:0.15 Tb3þ,yEu3þ phosphors. In addition, the fluorescence lifetimes energy transfer (hT) efficiency could also be estimated by formula (5) [41]:
hT ¼ 1
tS tS0
(5)
where ts0 and ts were the fluorescence lifetimes of the Tb3þ without and with the Eu3þ, respectively. The fluorescence lifetimes hT efficiency were also listed in Table 2. The hT efficiency increased with the increasing of the Eu3þconcentration and the highest was 98.34% when the doped content of the Eu3þ ions was 0.5 mol. All results strongly demonstrated that the energy transfer existed in SYBO:xTb3þ,yEu3þ and the fluorescence lifetimes were enough to apply to the promoting of WLEDs. The energy transfer in SYBO:xTb3þ, yEu3þ phosphors included the exchange interaction electric multipolar interaction mechanism. It could be analyzed by the combined formula (6) of Dexter's
Table 2 The fitting parameters value and average lifetime of Tb3þ in SYBO:0.15 Tb3þ, yEu3þ.
Fig. 5. The decay curves of Tb3þ ions in SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.1, 0.2, 0.3 and 0.5) phosphors (excited at 376 nm and monitored at 547 nm).
y/mol
A1
A2
t1/ms
t2/ms
tav/ms
h/%
0 0.1 0.2 0.3 0.5
208.883 699.44 590.794 671.035 609.763
98.963 39.405 18.139 4.654 0.949
3.8718 7.0633 11.9496 10.4194 10.0855
2912.2022 1878.653 1156.3166 669.9902 580.8526
2.904 1.762 0.868 0.214 0.057
e 39.33 70.11 90.63 98.34
16
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
energy transfer and Reisfeld's approximation formula [42e44]:
I0 fC n=3 I
(6)
In formula (6), C was the sum concentration of the doped ions and n was a parameter. Fig. 6 showed the relationships I0/I-C and I0/ I-Cn/3 (n ¼ 6, 8, 10). The relationships between I0/I-C and n ¼ 6, 8, and 10 were corresponding to the exchange interaction, the dipoledipole, the dipole-quadrupole and the quadrupole-quadrupole interaction, respectively. Obviously, the fitting parameter R2 was best only when n ¼ 6, implying that the electric dipoleedipole interaction was the main energy transfer mechanism in SYBO:xTb3þ,yEu3þ phosphors. Fig. 7 depicted the CIE chromaticity coordinate positions and the digital photographs of the SYBO:xTb3þ,yEu3þ phosphors under the wavelength of 376 nm excitation. Table 3 listed the CIE chromaticity coordinate as well as the CCT [45] values of the SYBO:0.15 Tb3þ,yTb3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) and SYBO:0.2Eu3þ phosphors. The CCT could be estimated by the following formula (7) [37]:
CCT ¼ 437n3 þ 601n2 6861n þ 5514:31
(7)
where n ¼ (x-xe)/(y-ye), (xe, ye) was the coordinate of the epicenter and its values was xe ¼ 0.3320, ye ¼ 0.1858. Moreover, the CCT firstly decreased and then increased, and it reached to maximums 1974 K when y ¼ 0.2 mol. With the increasing of Eu3þ, the color of the SYBO:xTb3þ,yEu3þ phosphors could tune from green (0.289, 0.457), light-white (0.373, 0.383) and finally adjust to
red (0.633, 0.365); the CIE tunable range was broader than the Y3Al2Ga3O12:Tb3þ,Eu3þ(from (0.4273, 0.5123) to (0.6193, 0.3801)) [22] and Gd2O2CN2:Tb3þ,Eu3þ (from (0.3134, 0.5454) to (0.5682, 0.3322)) [39] phosphors. SYBO:0.2Eu3þ (0.633, 0.365) was closer the National Television System Committee (NTSC) standard red phosphor (0.67, 0.33) than that two phosphors. The multicolor single-phase emissions phosphors were potentially attracted applications such as photoelectric equipment and liquid crystal displays.
4. Conclusions In conclusion, we had prepared a classes of multicolor tunable SYBO:xTb3þ,yEu3þ phosphors and investigated the luminescence properties. Under 376 nm excitation, SYBO:xTb3þ phosphors appeared intense green light, the critical quenching of the Tb3þ concentration was 0.15 mol and the critical distance between Tb3þTb3þ was 13.856 Å. According to analysis the luminescence spectra and the fluorescence lifetime curves, the energy transfer mechanism from Tb3þ to Eu3þin SYBO:xTb3þ,yEu3þ via dipoleedipole interaction as well as the energy transfer efficiency was as high as 96.48% and 98.34%. As the increase of the Eu3þ concentrations in the SYBO:xTb3þ,yEu3þ phosphors and depending the energy transfer, CIE coordinates could adjust from (0.289, 0.457), (0.373, 0.383) to (0.633, 0.365), which was corresponding to the color from green, light-white finally to red. All results showed that the SYBO:xTb3þ,yEu3þ phosphors could act as UV light excited multicolor tunable materials for WLEDs.
Fig. 6. The dependence of Is0/Is of Tb3þ on (a) C(Tb3þþEu3þ), (b) C(Tb3þþEu3þ)6/3, (c) C(Tb3þþEu3þ)8/3 and (d) C(Tb3þþEu3þ)10/3.
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11] Fig. 7. The CIE chromaticity coordinate positions and the digital photographs of the SYBO:0.15 Tb3þ,yEu3þ (y ¼ 0, 0.01, 0.05, 0.1, 0.2, 0.3 and 0.5) and SYBO:0.2Eu3þ phosphors.
[12]
[13] Table 3 The CIE chromaticity coordinate and CCT values of SYBO:xTb3þ,yEu3þphosphors. Sample
CIE coordinates (x, y)
CCT (K)
SYBO:0.15 Tb3þ SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.15 Tb3þ, SYBO:0.2Eu3þ
(0.289, (0.316, (0.373, (0.427, (0.484. (0.513, (0.539, (0.633,
6773 6016 4232 2607 1974 2625 3632 5228
0.01Eu3þ 0.05Eu3þ 0.1Eu3þ 0.2Eu3þ 0.3Eu3þ 0.5Eu3þ
0.457) 0.445) 0.383) 0.355) 0.332) 0.322) 0.324) 0.365)
[14]
[15]
[16]
[17]
Acknowledgement
[18]
This work was financially supported by the Innovation of Science and Technology Plan Projects of Shaanxi Province, China (Grant No. 2013KTDZ03-02-01, 2017TSCXL-GY-07-02), Scientific Research Program Funded by Shaanxi Provincial Education Department (Program No. 18JK0115), Research Starting Foundation from Shaanxi University of Science and Technology (Grant no.2016BJ-41), and the Graduate Innovation Fund of Shaanxi University of Science and Technology (Grant no. SUST-A04).
[21]
Appendix A. Supplementary data
[22]
Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.07.061.
[23]
[19]
[20]
References [24] [1] C. Ji, Z. Huang, X. Tian, W. Xie, J. Wen, H. He, C. Zhou, T. Zeng, Synthesis and
17
photoluminescence properties of a novel BaGe4O9:Eu3þ red emitting phosphor for warm white LEDs, Dyes Pigments 160 (2019) 772e778, https:// doi.org/10.1016/j.dyepig.2018.09.012. Z. Wang, F. Yuan, X. Li, Y. Li, H. Zhong, L. Fan, 53% Efficient Red Emissive Carbon Quantum Dots for High Color Rendering and Stable Warm WhiteLight-Emitting Diodes, 2017, pp. 1e7, https://doi.org/10.1002/ adma.201702910, 1702910. S.J. Park, B.S. Je, J.W. Jang, M.S. Oh, M.S. Koo, S.J. Yang, H.K. Yang, Green and red emitting YBO3:Ln3þ (Ln ¼ Eu, Tb) phosphors for detection of latent fingerprint, J. Alloy. Comp. 789 (2019) 367e374, https://doi.org/10.1016/ j.jallcom.2019.03.029. S. Liao, W. Zhang, J. Zhang, Site-sensitive energy transfer from Ce3þ to Tb3þ/ Mn2þ based on an efficient phosphor Li4SrCa(SiO4)2:Ce3þ, Ceram. Int. 44 (2018) 18413e18419, https://doi.org/10.1016/j.ceramint.2018.07.058. W. Zhang, H. Shen, X. li Hu, Y. Wang, J. fu Li, Z. jie Zhu, Z. yu You, C. yang Tu, Solid-state synthesis, structure and spectroscopic analysis of Dy:CaYAl3O7 phosphors, J. Alloy. Comp. 781 (2019) 255e260, https://doi.org/10.1016/ j.jallcom.2018.12.113. S. Zhu, X. Zhang, W. Li, M. Liu, L. Cheng, X. Mi, L. Lu, Phase transformation and luminescence properties of Y2.94Al5-xGaxO12:0.06Ce3þ phosphors, Ceram. Int. 45 (2018) 4964e4971, https://doi.org/10.1016/j.ceramint.2018.11.196. D.K. Singh, J. Manam, Efficient dual emission mode of green emitting perovskite BaTiO3: Er3þ phosphors for display and temperature sensing applications, Ceram. Int. 44 (2018) 10912e10920, https://doi.org/10.1016/ j.ceramint.2018.03.151. D.A. Hakeem, D.H. Kim, S.W. Kim, K. Park, Crystal structure and photoluminescence properties of novel garnet Y2-xLaCaGa3ZrO12:xLn3þ (Ln ¼ Eu and Tb) phosphors, Dyes Pigments 163 (2019) 715e724, https://doi.org/ 10.1016/j.dyepig.2018.12.045. Z. Leng, H. Xiong, L. Li, N. Zhang, Y. Liu, S. Gan, Facile controlled synthesis different morphologies of LuBO3:Ln3þ (Ln ¼ Eu, Tb) phosphors and tunable luminescent properties, J. Alloy. Comp. 646 (2015) 632e638, https://doi.org/ 10.1016/j.jallcom.2015.06.162. X. Huang, H. Guo, LiCa3MgV3O12:Sm3þ: a new high-efficiency white-emitting phosphor, Ceram. Int. 44 (2018) 10340e10344, https://doi.org/10.1016/ j.ceramint.2018.03.043. Q. Cheng, F. Ren, Q. Lin, H. Tong, X. Miao, High quantum efficiency red emitting a-phase La2W2O9:Eu3þ phosphor, J. Alloy. Comp. 772 (2018) 905e911, https://doi.org/10.1016/j.jallcom.2018.08.320. C. La, S. Po, Luminescence property and energy transfer behavior of apatitetype, Mater. Res. Bull. 108 (2018) 101e105, https://doi.org/10.1016/ j.materresbull.2018.08.040. X. Huang, H. Guo, A novel highly efficient single-composition tunable whitelight-emitting LiCa3MgV3O12:Eu3þ phosphor, Dyes Pigments 154 (2018) 82e86, https://doi.org/10.1016/j.dyepig.2018.02.047. J. Zhou, Z. Xia, Multi-color emission evolution and energy transfer behavior of La3GaGe5O16:Tb3þ,Eu3þ phosphors, Mater. Chem. C (2014) 2, https://doi.org/ 10.1039/C4TC01091D. X. Wu, Y. Jiao, O. Hai, Q. Ren, F. Lin, H. Li, Effect of single and composite fluxes on the morphology and luminescence properties of layered perovskite Sr1.95TiO4:0.05Sm3þ phosphor, J. Lumin. 192 (2017) 626e633, https://doi.org/ 10.1016/j.jlumin.2017.07.054. L. Li, X. Tang, Z. Wu, Y. Zheng, S. Jiang, X. Tang, G. Xiang, X. Zhou, Simultaneously tuning emission color and realizing optical thermometry via efficient Tb3þ/Eu3þ energy transfer in whitlockite-type phosphate multifunctional phosphors, J. Alloy. Comp. 780 (2019) 266e275, https://doi.org/10.1016/ j.jallcom.2018.11.378. W. Ma, J. Zhang, X. Zhang, X. Zhang, Y. Liu, S. Liao, S. Lian, Highly efficient and thermal stable La2Si2O7:Ce3þ,Tb3þ,Eu3þ phosphors: emission color tuning through terbium bridge, J. Alloy. Comp. 785 (2019) 53e61, https://doi.org/ 10.1016/j.jallcom.2019.01.194. T. Dogan, L. Tormo, S. Akca, N. Kucuk, J.G. Guinea, Y. Karabulut, M. Ayvacikli, M. Oglakci, M. Topaksu, N. Can, Cathodoluminescence and thermoluminescence of ZnB2O4:Eu3þ phosphors prepared via wet-chemical synthesis, Ceram. Int. 45 (2019) 4918e4925, https://doi.org/10.1016/j.ceramint.2018.11.191. D. Zhang, G. Li, W. Yang, W. Huang, Z. Leng, S. Fang, L. Li, Tunable photoluminescence properties and energy transfer of Ca5(BO3)3F:Tb3þ/Eu3þ phosphors for solid state lighting, J. Lumin. 208 (2019) 155e163, https://doi.org/ 10.1016/j.jlumin.2018.12.022. J. Zhang, G.M. Cai, G.X. Zhang, Z.P. Jin, Insight into crystal structure and Eu/Tb doped luminescence property of a new phosphate, J. Alloy. Comp. 762 (2018) 444e455, https://doi.org/10.1016/j.jallcom.2018.05.079. X. Zhang, J. Zhang, Y. Chen, M. Gong, Energy transfer and multicolor tunable emission in single-phase Tb3þ, Eu3þ co-doped Sr3La(PO4)3 phosphors, Ceram. Int. 42 (2016) 13919e13924, https://doi.org/10.1016/j.ceramint.2016.05.202. Z. Li, B. Zhong, Y. Cao, S. Zhang, Y. Lv, Z. Mu, Z. Hu, Y. Hu, Energy transfer and tunable luminescence properties in Y3Al2Ga3O12:Tb3þ,Eu3þ phosphors, J. Alloy. Comp. 787 (2019) 672e682, https://doi.org/10.1016/ j.jallcom.2019.02.154. D. Wen, J. Feng, J. Li, J. Shi, M. Wu, Q. Su, K2Ln(PO4)(WO4):Tb3þ,Eu3þ (Ln ¼ Y, Gd and Lu) phosphors: highly efficient pure red and tuneable emission for white light-emitting diodes, J. Mater. Chem. C. 3 (2015) 2107e2114, https:// doi.org/10.1039/c4tc02406k. J.Y. Si, N. Liu, S.Y. Song, G.M. Cai, N. Yang, Z. Li, Investigation on Eu/Tb activated photoluminescent properties of Li3Sc(BO3)2 based phosphors, J. Alloy. Comp.
18
X. Wu et al. / Journal of Alloys and Compounds 805 (2019) 12e18
719 (2017) 171e181, https://doi.org/10.1016/j.jallcom.2017.05.161. [25] Z. Chen, X. Chen, S. Huang, Y. Pan, A novel tunable green-to-red emitting phosphor Ca4Lao(BO3)3:Tb,Eu via energy transfer with high quantum yield, Ceram. Int. 42 (2016) 13476e13484, https://doi.org/10.1016/ j.ceramint.2016.05.139. [26] Y. Zhang, X. Zhang, H. Zhang, Z.-C. Wu, Y. Liu, L. Ma, X. Wang, W.-R. Liu, B. Lei, Enhanced absorption of Sr3Lu2(BO3)4:Ce3þ,Tb3þ phosphor with energy transfer for UV-pumped white LEDs, J. Alloy. Comp. 789 (2019) 215e220, https://doi.org/10.1016/j.jallcom.2019.03.088. [27] X. Wu, J. Zheng, Q. Ren, W. Bai, Y. Ren, O. Hai, Synthesis and luminescent properties of a novel orange-red Ba3Y(BO3)3:Sm3þ phosphors for white LEDs, Polyhedron 164 (2019) 17e22, https://doi.org/10.1016/j.poly.2019.02.031. [28] T. Jiang, Y. Chen, X. Gong, Y. Lin, J. Huang, Z. Luo, Y. Huang, Spectroscopic Properties of Dy3þ-Doped Sr3Y(BO3)3 Crystal, vol 91, 2019, pp. 171e176, https://doi.org/10.1016/j.optmat.2019.03.004. [29] R. Simura, S. Kawai, K. Sugiyama, T. Yanagida, T. Sugawara, T. Shishido, A. Yoshikawa, Valence state of dopant and scintillation properties of Ce-doped Sr3Y(BO3)3 crystal, J. Cryst. Growth 362 (2013) 296e299, https://doi.org/ 10.1016/j.jcrysgro.2011.11.089. [30] K.A. Denault, Z. Cheng, J. Brgoch, S.P. Denbaars, R. Seshadri, Structurecomposition relationships and optical properties in cerium-substituted (Sr,Ba)3(Y,La)(BO3)3 borate phosphors, J. Mater. Chem. C. 1 (2013) 7339e7345, https://doi.org/10.1039/c3tc31621a. [31] D. Zhao, G. Wang, Growth and Spectroscopic Characterization of Er3þ : Sr3Y(BO3)3 Crystal, vol 130, 2010, pp. 424e428, https://doi.org/10.1016/ j.jlumin.2009.10.007. [32] X. Meng, L. Zhang, G. Wang, Growth and Spectral Properties of Tm3þ-Doped Sr3Y(BO3)3 Crystal, vol 481, 2009, pp. 354e357, https://doi.org/10.1016/ j.jallcom.2009.02.136. [33] H. Xu, Z. Xia, H. Liu, L. Liao, Luminescence properties and energy transfer in La5-x-ySi2BO13:xCe3þ, yTb3þ phosphor, ECS J. Solid State Sci. Technol. 2 (2013) R186eR189, https://doi.org/10.1149/2.035309jss. [34] X. Wu, Y. Jiao, Q. Ren, O. Hai, F. Lin, H. Li, W. Bai, Photoluminescence and energy transfer in Sr3La(BO3)3:Ce, Sm and Sr2TiO4:Sm, Eu phosphors, Optic Laser. Technol. 108 (2018) 456e465, https://doi.org/10.1016/ j.optlastec.2018.07.043. [35] B. Li, X. Huang, H. Guo, Y. Zeng, Energy transfer and tunable photoluminescence of LaBWO6:Tb3þ,Eu3þ phosphors for near-UV white LEDs, Dyes
Pigments 150 (2018) 67e72, https://doi.org/10.1016/j.dyepig.2017.11.003. [36] M. Chen, Z. Xia, Q. Liu, Luminescence properties and energy transfer of Ce3þ/ Tb3þ co-doped Ca6Ba(PO4)4O phosphor for near-UV pumped light-emitting diodes, J. Mater. Chem. C. 3 (2015) 4197e4204, https://doi.org/10.1039/ c5tc00358j. [37] X. Wu, W. Bai, O. Hai, Q. Ren, F. Lin, Y. Jiao, Structure, luminescence properties and energy transfer of Dy3þ and Eu3þ codoped KBa(VO4) phosphor, J. Solid State Chem. 265 (2018) 109e116, https://doi.org/10.1016/j.jssc.2018.05.033. [38] Y. Fang, X. Tian, J. Liu, Y. Zhang, Y. Liu, G. Zhao, J. Zou, N. Vainos, J. Hou, Trichromatic emission from a single-phase Na5Y4(SiO4)4F:Eu2þ,Tb3þ,Eu3þ phosphor for white-light-emitting diodes, J. Lumin. 207 (2018) 34e40, https:// doi.org/10.1016/j.jlumin.2018.10.010. , F. Tessier, G. Chen, Novel color-tunable [39] S. Yuan, L. Wang, Y. Yang, F. Chevire Gd2O2CN2:Tb3þ,Eu3þ phosphors: characterization and photoluminescence properties, Ceram. Int. 42 (2016) 12508e12511, https://doi.org/10.1016/ j.ceramint.2016.04.059. [40] Q. Ren, F. Lin, X. Wu, O. Hai, T. Wei, Y. Jiao, H. Li, Synthesis and luminescent properties of KGd(MoO4)2:Sm3þ red phosphor for white light emitting diodes, Mater. Res. Bull. 90 (2017) 66e72, https://doi.org/10.1016/ j.materresbull.2017.02.023. [41] H. Lai, J. Zhang, D. Hou, H. Guan, X. Ye, Luminescence characteristics and energy transfer of Eu2þ/Tb3þ doped single phase multi-color phosphor, Ceram. Int. 44 (2018) 15072e15078, https://doi.org/10.1016/ j.ceramint.2018.05.140. [42] Z. Xia, Y. Liang, D. Yu, M. Zhang, W. Huang, M. Tong, J. Wu, J. Zhao, Photoluminescence properties and energy transfer in color tunable BaY2Si3O10: Ce,Tb phosphors, Optic Laser. Technol. 56 (2014) 387e392, https://doi.org/ 10.1016/j.optlastec.2013.09.014. [43] M. Jiao, Y. Jia, W. Lü, W. Lv, Q. Zhao, B. Shao, H. You, Sr3GdNa(PO4)3F: Eu2þ,Mn2þ: a potential color tunable phosphor for white LEDs, J. Mater. Chem. C. 2 (2014) 90e97, https://doi.org/10.1039/c3tc31837k. [44] X. Wu, Y. Jiao, O. Hai, Q. Ren, F. Lin, H. Li, Photoluminescence, energy transfer, color tunable properties of Sr3La(BO3)3:Ce, Tb phosphors, J. Alloy. Comp. 730 (2018) 521e527, https://doi.org/10.1016/j.jallcom.2017.10.022. [45] H. Xiong, Y. Zhang, Y. Liu, T. Gao, L. Zhang, Z.A. Qiao, L. Zhang, S. Gan, Q. Huo, Self-template construction of honeycomb-like mesoporous YPO4:Ln3þ (Ln ¼ Eu, Tb) phosphors with tuneable luminescent properties, J. Alloy. Comp. 782 (2019) 845e851, https://doi.org/10.1016/j.jallcom.2018.12.107.