- Email: [email protected]
Enhancement of the persistent luminescence of Sr2MgSi2O7:Eu2+,Dy3+ by Cu nanoparticles
Journal Pre-proof Enhancement of the persistent luminescence of Sr2MgSi2O7:Eu nanoparticles
2+ 3+ ,Dy by Cu
Ou Hai, Enlong Yang, Qiang Ren, Xiulan Wu, Yuhan Ren, Yujing Zhao, Jianfeng Zhu PII:
S0022-2313(19)31635-7
DOI:
https://doi.org/10.1016/j.jlumin.2019.116965
Reference:
LUMIN 116965
To appear in:
Journal of Luminescence
Received Date: 20 August 2019 Revised Date:
11 December 2019
Accepted Date: 11 December 2019
Please cite this article as: O. Hai, E. Yang, Q. Ren, X. Wu, Y. Ren, Y. Zhao, J. Zhu, Enhancement of 2+ 3+ the persistent luminescence of Sr2MgSi2O7:Eu ,Dy by Cu nanoparticles, Journal of Luminescence (2020), doi: https://doi.org/10.1016/j.jlumin.2019.116965. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier B.V.
Enhancement of the persistent luminescence of Sr2MgSi2O7:Eu2+,Dy3+ by Cu nanoparticles Ou Hai*, Enlong Yang*, Qiang Ren, Xiulan Wu, Yuhan Ren, Yujing Zhao, Jianfeng Zhu 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 Abstract: The persistent luminescence (PersL) phosphors are excellent energy-saving and environment-friendly materials. Here, Cu nanoparticles(CuNP) were deposited on the surface of Sr2MgSi2O7:Eu2+,Dy3+ (SMS) in the CuCl2 solution by photo-reduction deposition method for the first time, the initial brightness increases 1.1 times and the light response ranges are broadened to visible light. With the increasing of CuCl2 concentration, the PersL intensity of SMS increases to its maximum and then decreases, reaches the best at 0.3mmol/L CuCl2 solution. The changes of PersL intensity and absorption intensity indicate that CuNP can produce plasma effect (PE) on the surface of SMS, which efficiently increase the number of photo-generated electrons and holes, results more electrons can be trapped. For long afterglow materials, more electrons are captured by traps means that more electrons can be released to produce afterglow after remove the external light, thereby the PersL performance are effectively improved. In this paper, we used a simple method to improve the PersL performance of SMS and discussed the influence mechanism of *Corresponding author. Tel:8615091890116; 8613119136072; Email address: [email protected](O. Hai); [email protected](Enlong. Y).
CuNP in SMS. This result is attributed to the unique luminescence mechanism of long afterglow materials and the PE of CuNP. Our researches promote the application of SMS and provide a strategy for improving PersL of various long afterglow materials. Keywords:
Persistent
luminescence;
Cu
nanoparticles;
Plasmon
effect;
Photoluminescence; Afterglow phosphors 1. Introduction Long afterglow luminescence material, also called long phosphor powder, is an important energy-saving and environmental material. As a kind of excellent energy storage materials, long afterglow materials can store light energy and gradually release from several minutes to hours after being excited [1]. Nowadays, this material has been widely used in some field, such as traffic, safety, medical, electrical appliances and information storage [2-6]. Furthermore, it is reported to be a new photocatalysis material [7]. Silicates doped with the rare earth elements have been reported as a new kind of afterglow materials. The Eu2+ and Dy3+ co-dope Sr2MgSi2O7:Eu2+,Dy3+(SMS) materials have good chemical stability, thermal stability and low cost, which has attracted the attention of many researches [8, 9]. But its PersL performance is less than aluminate systems. Currently, the main methods to improve the PersL are ion doping, change of the synthesis methods and so on [10-12]. However, these methods are complex and high cost. Therefore, it is still a challenge to improve the PersL of SMS. For long afterglow materials, there are electrons and holes in the luminescence center. The excited electrons can be captured by the traps inside the materials when the material excited by the light source and the recombination of
electrons and holes can produce visible light after the excitation stops [8, 13]. In recent years, due to its unique optical properties, the PE of metals nanoparticles has been widely studied, such as photocatalysis and plasma-enhanced fluorescence [14-17]. In the photocatalysis filed, it has been proved that the PE produce by CuNP can promote the separation of electrons and holes for photocatalysis materials and result in more electrons available [18, 19]. In other words, the mobility of electrons can be increased by CuNP. However, for long afterglow materials, the study of PE enhancing PersL is weak relatively and the enhancement mechanism of PE is also rarely reported. In this paper, we took SMS as the research object. CuNP were deposited on the surface of SMS by traditional photo-reduction deposition method for the first time. The PE is achieved on the surface of SMS by controlling the deposition amounts of Cu, which can enhance the PersL performance and broaden the light response range of SMS. Furthermore, with the amounts of Cu deposition increase, the PersL intensity first increases and then decreases, reaching the best at 0.3mmol/L CuCl2 concentration. The initial brightness of SMS was increased by a factor of 1.1 at 0.3mmol/L CuCl2 concentration. In this paper, we provide a method for enhancing of the PersL and discuss the enhancement mechanism of Cu through the luminescence characteristic of long afterglow materials.
2. Experiments and measurements 2.1 Synthesis of SrMgSi2O7:Eu2+,Dy3+ Polycrystalline
powders
Sr1.96MgSi2O7:0.02Eu2+,0.02Dy3+(SMS)
were
synthesized via high-temperature solid-state synthesis according to the starting reagents:SrCO3(AR),
MgO(AR),
SiO2(AR),
H3BO3(AR),
Eu2O3(99.99%)
Dy2O3(99.9%) from Sinopharm Chemical Reagent Co., Ltd. (China). Additionally, 3mol% H3BO3 was added as flux. The reacted product was sintered at a temperature of 1240 3
, holding time is 2h, the heating rate is 5
/min, and then cooled at a rate of
/min. The entire sintering process was carried out in reducing gas flow
(10at.%H2+90at.%Ar). Then sample was added to the alcohol and was washed for 30minutes in ultrasonic wave. Finally, samples were obtained for the experiment. 2.2 Synthesis of Cu/SrMgSi2O7:Eu2+,Dy3+ The
Cu/SrMgSi2O7:Eu2+,Dy3+(Cu/SMS)
were
synthesized
through
the
photo-reduction deposition method. The brief experimental steps are shown in Fig.1. 1g SMS and 10ml various mole concentration of CuCl2 solutions (0.2, 0.25, 0.30, 0.35, 0.5, and 1.5mmol/L) were mixed in the light reactor. 100ml deionized water were added to the above reactor and the mixed solution was stirred in the dark for 10min to achieve pre-adsorption. A 250w uv light with main wavelength of 365nm was used as a reducing light. The mixture was reduced for 30min in an ultrasound apparatus and the Cu2+ was reduced into zerovalent Cu. The mixtures were then dried in a vacuum oven at 80˚C and were labeled as Cu/SMS-1, Cu/SMS-2, Cu/SMS-3, Cu/SMS-4, Cu/SMS-5 and Cu/SMS-6 respectively. Finally, we got the samples with different amounts of Cu deposition.
Fig.1. The flow chart of photo-reduction deposition method for Cu/SMS preparation. 2.3 Measurements The samples were characterized by X-ray powder diffraction (Rigaku D/Max-2200 type, Japan) with Cu Kα radiation (λ=1.5406Å). The surface morphologies of the samples were observed by scanning (FESEM, FEI . Verious 460, American)
and
transmission
electron
microscopy(TEM;
FEI
Tecnai
G2
hight-resolution transmission electron microscope). The uv-vis diffuse-reflection spectra were obtained on a uv-vis-near-IR spectrometer (Edinburgh FS5). The PL spectra were measured by the Hitachi F4600 Fluorescence spectrometer. The persistent luminescence curves were obtained by a PersL material optical test system using an artificial light as a light source with the irradiation time of 10min. All of the above measurements were taken at room temperature. 3. Results and discussion 3.1 Structure and Morphology of SMS and Cu/SMS The SMS was synthesized by high temperature solid state reaction method at
1240 . The XRD pattern (Fig. 2(a)) shows that the initial sample have a pure diffraction peaks, all of which are indexed to tetragonal Sr2MgSiO7 structure (space group:P-421m,No,113,JCPDS card: 75-1736). This indicates that the crystal structure of the host material was not changed by doped Eu2+ and Dy3+. Fig. 2(b) shows that the shape of SMS is blocky and the surface is smooth with no impurities attached, which provides an advantage for Cu deposition. The photoluminescence (PL) spectrum of SMS is shown in Fig. 2(c) with the excitation and emission are located at 361nm and 465nm respectively, which belongs to the characteristic peak of Eu2+ doped in the Sr2MgSi2O7 matrix [11, 12]. As shown in Fig. 2(d), the final material has a good PersL, which is attributed to a suitable trap depth produced by the introduction of Dy3+ [20].
Fig.2. (a) The XRD pattern of SMS; (b) The SEM image of SMS; (c) The excitation and emission spectrums of SMS; (d) The PersL curve of SMS. Fig. 3(a) and (b) shows the TEM images of SMS without Cu and Cu/SMS-3 respectively. It can be seen from Fig. 3(b) that after treatment with CuCl2 solution, many black particles distribute on the surface of SMS. Fig. 3(c) and (d) display the TEM images of Cu/SMS-3 and the result shows that CuNP distribute on the surface of SMS evenly with the shape of spherical. In this study, the grain size and distribution of Cu particles have a great impact on the PersL performance. We made a measure for the grain size of CuNP and the distance between different CuNP. As shown in the inset bar chart, the diameter is about 3nm and the distance is about 4-5nm. According to previous reports, we can conclude that the shape of CuNP has a great impact on the experimental results, which will be further studied in our following work. In order to prove that different amounts of Cu were deposited on the surface of SMS, the energy dispersive X-ray spectroscopy (EDS) was used for elemental mapping. Fig. 4(a) and (b) show the SEM images of SMS and Cu/SMS-3. Fig. 4(c) shows the elemental O mapping image of Cu/SMS-3. Fig. 4(d), (e) and (f) shows the elemental Cu mapping images in Cu/SMS-1, Cu/SMS-3 and Cu/SMS-6 respectively, indicating that CuNP are deposited on the surface of SMS with different amounts. Furthermore, as can be seen in the Fig. 4(f), large amounts of Cu were deposited on the surface of the SMS and the color of the sample became blue significantly. As the amounts of Cu deposition increases, the absorption light area of SMS reduced gradually. For long persistence materials, the effective contact area between SMS and
light reduced, which partly affects the luminescence performance.
Fig. 3. (a) The TEM image of SMS; (b), (c) and (d) are the TEM images of Cu/SMS-3.
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 4. (a) and (b) are the SEM images of SMS and Cu/SMS-3 respectively; (c) The elemental O mapping image in Cu/SMS-3; (d), (e) and (f) are the elemental Ag mapping images in Cu/SMS-1, Cu/SMS-3 and Cu/SMS-6 respectively.
3.2 Chemical Composition of Cu/SMS To investigate the surface elemental composite and the valence state of Cu on the surface of SMS, XPS and AES analyses were used to characterize the Cu/SMS-3. Fig. 5(a) shows the full surface survey of Cu/SMS-3, which confirms the presence of various elements (O, Si, Sr, Mg and Cu) on the surface of SMS. The high resolution spectrums of O, Sr, Si and Mg in SMS are shown in Fig. 5(b), these peaks are assigned to 530eV, 132ev, 100ev and 1300ev respectively, indicating the sample has good crystallinity, which is agreement with previous reports [21]. Fig. 5(c) shows the high resolution spectrum of Cu2p2/3, the binding energy peak at 932.6eV, which indicates the possibility of Cu0 and Cu+ [19]. Combing with the auger electron spectrum of Cu(Fig. 5(d)), Cu0 was found on the surface of SMS with the binding
energy is 568.3ev, which can be confirmed by the previous research [22-24]. The results of XPS and AES analysis provide a favorable evidence for the existence of metallic Cu.
Fig.5. (a) The full spectrum of Cu/SMS-3; (b) The high resolution spectrums of O1s, Sr3d, Si2p and Mg1s respectively; (c) and (d) are the high resolution spectrum of Cu2p and the LMM Auger spectrum of Cu respectively.
3.3 Absorption spectra Fig. 6(a) shows the uv-vis absorption spectrum of SMS and Cu/SMS. Compared with the initial sample, the absorption intensity gradually increases with the increasing of Cu deposition amounts. To make it clear that Cu promotes the absorption of SMS, Fig. 6(b) shows the absorption of SMS, Cu/SMS-1 and Cu/SMS-6 respectively, and
we can see that the absorption of samples in uv region is significantly enhanced after Cu deposition. When the CuNP are excited, it can generate a PE and form an electrostatic field on the surface of the SMS, which effectively promotes the separation and transfer of electrons and holes in the luminescence center. More electrons are excited and captured by traps, resulting in an increase in the absorption intensity. This is consistent with the results of PersL.
Fig. 6. (a) The absorption spectrum of SMS and Cu/SMS; (b) The absorption spectrum of SMS, Cu/SMS-3 and Cu/SMS-6. 3.4 Photoluminescence(PL) performance Fig. 7(a) and (b) shows the excitation and emission spectra of SMS and Cu/SMS respectively. All samples were excited at 365nm and monitored at 468nm. The excitation range is mainly between 250nm and 450nm. The emission spectra of these phosphors have a broad band peak around 470nm, which is attributed to the electrical transitions 4f65d1→4f7 of Eu2+ [25]. Compared with the initial sample, deposition of Cu had no obvious effect on the position of the peak, but the intensities of the excitation and emission are obviously decreased. This is consistent with our expectation and the change of PL spectrums is attributed to the PE of CuNP. CuNP on
the surface of SMS allows more photo-generated electrons to be transferred and then captured, reducing recombination rate of electrons and holes. More electrons are captured by traps, resulting in lower emission spectra.
Fig. 7. (a) and (b) are the excitation and emission spectra of SMS and Cu/SMS respectively. 3.5 The persistent luminescence curves After removing the excitation light source, the change of afterglow luminescence with the time is called PersL performance. All samples were excited under 25W uv lamp for 10 minutes. Fig. 8(a) presents the afterglow decay curves of the SMS and Cu/SMS. Obviously, appropriate amounts of Cu deposition can improve the PersL of SMS. When the CuCl2 concentration is 0.3mmol/L, the PersL performance is the best, and the initial luminescence increased by 1.1 times. Fig. 8(b) shows the PersL curves of SMS and Cu/SMS-3 within 30min, and the luminescence intensity of Cu/SMS-3 is significantly better than SMS. This is because CuNP produce PE after excited, which forms a near electrostatic filed on the surface of SMS, promoting the separation of electrons and holes. For long persistence luminescent materials, there are traps to capture electrons in the luminescent center [8]. When the excitation stops, the
recombination of the captured electrons and holes will produce afterglow. Due to the PE of Cu, the electrostatic filed produced by Cu promotes the separation of electrons and holes, so that more electrons are transferred and captured by traps, thus improves PersL performance. In order to accurately study the effect of different amounts of Cu deposition on the PerL of SMS, the luminescence intensity at 0min and 5min (Fig. 8(c)) show that with the increase of Cu amounts, the PersL performance increases to its maximum and then decreases, reaching the best in the 0.3mmol/L CuCl2 solution. However, with a large amount of Cu deposited on the surface of SMS, the PersL decreased gradually and lower than SMS. This may be because the amounts of Cu deposition are too much, which reduces the effective contact area between SMS and light and less light can reach the luminescence center. For long afterglow materials, different trap depth has great influence on the luminescence performance [4, 26]. In order to further study the effect of Cu on the depth of traps, we used the following equation to analyze the long afterglow curve [20]. I =Ic+A1exp(-t/τ1) + A2exp(-t/τ2)
(1)
where I is the luminescence intensity, t is the time, A1 and A2 are the constants, τ1 and τ2 are the decay constants, respectively. It is well known that τ1 and τ2 represents the fast and slow decay process respectively. It can be seen from the fitting results in Table1, as the concentration of CuCl2 solution increases, τ1 and τ2 decrease first and then increase. According to above conclusion, more electrons are captured due to the PE of Cu, which means that they are more likely to be released, so the proper Cu
reduce the depth of the trap. The normalized decay curves and the fitting process are shown in Fig. S1.
Fig. 8. (a) The PersL curves of SMS and Cu/SMS; (b) The PersL curves of SMS and Cu/SMS-3; (c) The luminescence intensity of SMS a0min and 5min.
Table 1 The fitting results of the decay curves treated by different CuCl2 concentration. CuCl2 (mmol/L)
τ1
τ2
0 0.2 0.25 0.3 0.35 0.8 1.5
9.21 6.55 6.16 5.43 5.91 6.25 4.91
92.94 67.96 64.30 59.98 59.86 66.91 43.98
3.6 The mechanism of Cu enhancing persistent luminescence performance As a kind of plasma material, CuNP can promote the separation and inhibit the recombination of photo-generated electrons and holes in semiconductor materials, which has been proved in photocatalysis field [14, 27-29]. In other words, the mobility of photo-generated electrons can be increased by PE of CuNP. For SMS, there are free electrons and traps in the luminescence center and these electrons can be captured by traps after being excited. However, according previous studies, the emission mechanism of long afterglow material is still debatable [9, 12]. Here, the emission mechanism of SMS and the enhancement mechanism of Cu are proposed as follows (Fig. 9). When electrons in the ground state 4f of Eu2+ are excited to the energy level of 5d, some of them return to the grate state forming a unique emission of Eu2+ [30]. Another part are transferred to the conduction band and captured by traps(Vo" or DySr ) of SMS (The path is represented by a solid black line). Meanwhile, Eu2+ becomes Eu3+, and Dy3+ becomes Dy2+, which can be confirmed from previous reports [21]. After the external light source is removed, these captured
electrons are released and recombined with Eu2+ to produce PersL (The path is represented by a red dotted line). As shown in Fig. 9, When the Cu/SMS excited by the light, the luminescence center of SMS can generate the separation of electrons and holes. At the same time, CuNP can produce PE, which produces an electrostatic field on the surface of SMS [31]. Under an external electrostatic field, these excited electrons are more easily separated, transferred and captured by traps. This indicates that more electrons are captured by traps than that in the absence of electrostatic field. For long afterglow materials, more electrons are captured by traps means that more electrons can be released after remove the external light, thus results in a better PersL.
Fig.9. The Schematic diagram of Cu enhancing PersL performance, the purple sphere is SMS, the green sphere is Cu nanoparticles, the black dotted line represents the plasma enhancement effect. 4. Conclusions In summary, Cu/SMS phosphors with varying amounts of Cu deposition were
synthesized by a simple method. XPS and AES confirmed the presence of Cu0 on the surface of SMS. The PersL intensity is effectively improved and the initial brightness is increased by 1.1 times in 0.3mm/L CuCl2 solution. The light response range of SMS is broadened to visible light after Cu deposited. With the number of captured electrons and holes increasing, they are more likely to be released, thus reduce the depth of the trap. The improvement of PersL performance is attributed to the unique luminescence mechanism of SMS and PE of Cu. Our researches promote the application of long afterglow materials and provide a strategy to enhance the PersL performance for various afterglow materials. Acknowledgements This work was financially supported by Natural Science Foundation of Shaanxi Province (Grant No. 2019JQ-785), 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). References: [1] Y. Li, M. Gecevicius, J. Qiu, Long persistent phosphors—from fundamentals to applications, Chemical Society Reviews, 45 (2016) 2090-2136. [2] O. Hai, H. Jiang, Q. Zhang, Q. Ren, X. Wu, J. Hu, Effect of cooling rate on the microstructure and luminescence properties of Sr2MgSi2O7:Eu(2+),Dy(3+) materials, Luminescence:the journal of biological and chemical luminescence, 32(2017) 1442-1447.
[3] M.A. Tshabalala, H.C. Swart, F.B. Dejene, E. Coetsee, O.M. Ntwaeaborwa, Structure, surface analysis, photoluminescent properties and decay characteristics of Tb3+-Eu3+ co-activated Sr2MgSi2O7 phosphor, Applied Surface Science, 360 (2016) 409-418. [4] J. Ueda, S. Miyano, S. Tanabe, Formation of Deep Electron Traps by Yb(3+) Codoping Leads to Super-Long Persistent Luminescence in Ce(3+)-Doped Yttrium Aluminum Gallium Garnet Phosphors, ACS Appl Mater Interfaces, 10 (2018) 20652-20660. [5] H. Wu, Y. Hu, B. Zeng, Z. Mou, L. Deng, Tunable luminescent properties by adjusting the Sr/Ba ratio in Sr1.97−xBaxMgSi2O7:Eu2+0.01,Dy3+0.02 phosphors, Journal of Physics and Chemistry of Solids, 72 (2011) 1284-1289. [6] Y. Zhuang, Y. Lv, L. Wang, W. Chen, T.L. Zhou, T. Takeda, N. Hirosaki, R.J. Xie, Trap Depth Engineering of SrSi2O2N2:Ln(2+),Ln(3+) (Ln(2+) = Yb, Eu; Ln(3+) = Dy, Ho,Er) Persistent Luminescence Materials for Information Storage Applications, ACS Appl Mater Interfaces, 10 (2018) 1854-1864. [7] G Cui, X Yang, Y Zhang, Y Fan, P Chen, H Cui, Y Liu, X Shi, Q Shang, B Tang. Round-the-clock photocatalytic hydrogen production with high efficiency by a long afterglow
material[J].
Angewandte
Chemie
International
Edition,
58(2019):1340-1344. [8] O. Hai, Q. Ren, X. Wu, Q. Zhang, Z. Zhang, Z. Zhang, Insights into the element gradient in the grain and luminescence mechanism of the long afterglow material Sr2MgSi2O7:Eu2+,Dy3+, Journal of Alloys and Compounds, 779 (2019) 892-899.
[9] O. Hai, Z. zhang, Q. Ren, X. Wu, Q. Zhang, B. Zeng, D. Li, The preparation and functional studies of the porous long afterglow luminescent materials, Dyes and Pigments, 156 (2018) 160-166. [10] E. Finley, A. Cobb, A. Duke, A. Paterson, J. Brgoch, Optimizing Blue Persistent Luminescence in (Sr1−δBaδ)2MgSi2O7:Eu2+,Dy3+ via Solid Solution for Use in Point-of-Care Diagnostics, ACS Applied Materials & Interfaces, 8 (2016) 26956-26963. [11] H. Wu, Y. Hu, Y. Wang, C. Fu, Influence on the luminescence properties of the lattice defects in Sr2MgSi2O7:Eu2+,M (M=Dy3+,La3+ or Na1+), Journal of Alloys and Compounds, 497 (2010) 330-335. [12] L. Xiao, J. Zhou, G. Liu, L. Wang, Luminescent properties of R+ doped Sr2MgSi2O7:Eu2+,Dy3+(R+ = Li+, Ag+) phosphors, Journal of Alloys and Compounds, 712 (2017) 24-29. [13] B. Liu, C. Shi, M. Yin, L. Dong, Z. Xiao, The trap states in the Sr2MgSi2O7 and (Sr,Ca)MgSi2O7 long afterglow phosphor activated by Eu2+ and Dy3+, Journal of Alloys and Compounds, 387 (2005) 65-69. [14] S. Chen, X. Li, W. Zhou, S. Zhang, Y. Fang, Carbon-coated Cu-TiO2 nanocomposite with enhanced photostability and photocatalytic activity, Applied Surface Science, 466 (2019) 254-261. [15] Y. Gan, M. Zhang, J. Xiong, J. Zhu, W. Li, C. Zhang, G. Cheng, Impact of Cu particles on adsorption and photocatalytic capability of mesoporous Cu@TiO2 hybrid towards ciprofloxacin antibiotic removal, Journal of the Taiwan Institute of Chemical
Engineers, 96 (2019) 229-242. [16] W. Ye, Q. Huang, X. Jiao, X. Liu, G. Hu, Plasmon-enhanced fluorescence of CaF 2:Eu
2+
nanocrystals by Ag nanoparticles, Journal of Alloys and Compounds, 719
(2017) 159-170. [17] B. Zhang, Y. Chen, J. Li, E. Pippel, H. Yang, Z. Gao, Y. Qin, High Efficiency Cu-ZnO Hydrogenation Catalyst: The Tailoring of Cu-ZnO Interface Sites by Molecular Layer Deposition, ACS Catalysis, 5 (2015) 5567-5573. [18] P.K. Baruah, A.K. Sharma, A. Khare, Effective control of particle size, surface plasmon resonance and stoichiometry of Cu@CuxO nanoparticles synthesized by laser ablation of Cu in distilled water, Optics & Laser Technology, 108 (2018) 574-582. [19] J. Qiu, N.E. Richey, J.S. DuChene, Y. Zhai, Y. Zhang, L. McElwee-White, W.D. Wei, Surface Plasmon-Mediated Chemical Solution Deposition of Cu Nanoparticle Films, The Journal of Physical Chemistry C, 120 (2016) 20775-20780. [20] H. Wu, Y. Hu, Y. Wang, B. Zeng, Z. Mou, L. Deng, W. Xie, Influence on luminescent properties of the Sr2MgSi2O7:Eu2+ by Dy3+,Nd3+ co-doping, Journal of Alloys and Compounds, 486 (2009) 549-553. [21] G Cui, X Yang, Y Zhang, Y Fan, P Chen, H Cui, Y Liu, X Shi, Q Shang, B Tang. Round-the-clock photocatalytic hydrogen production with high efficiency by a long afterglow
material[J].
Angewandte
Chemie
International
Edition,
58(2019):1340-1344.. [22] T. Ghodselahi, H. Zahrabi, M.H. Saani, M.A. Vesaghi, CO Gas Sensor Properties
of Cu@CuO Core–Shell Nanoparticles Based on Localized Surface Plasmon Resonance, The Journal of Physical Chemistry C, 115 (2011) 22126-22130. [23] J. Gong, H. Yue, Y. Zhao, S. Zhao, L. Zhao, J. Lv, S. Wang, X. Ma, Synthesis of ethanol via syngas on Cu/SiO2 catalysts with balanced Cu0-Cu+ sites, J Am Chem Soc, 134 (2012) 13922-13925. [24] J. Hernandez, P. Wrschka, G.S. Oehrlein, Surface Chemistry Studies of Copper Chemical Mechanical Planarization, Journal of The Electrochemical Society, 148 (2001) G389. [25] R. Shrivastava, J. Kaur, Characterisation and Mechanoluminescence studies of Sr2MgSi2O7:Eu2+,Dy3+, Journal of Radiation Research and Applied Sciences, 8 (2019) 201-207. [26] E. Finley, A. Mansouri Tehrani, J. Brgoch, Intrinsic Defects Drive Persistent Luminescence in Monoclinic SrAl2O4:Eu2+, The Journal of Physical Chemistry C, 122 (2018) 16309-16314. [27] X. Guo, X. Li, L. Qin, S.-Z. Kang, G. Li, A highly active nano-micro hybrid derived from Cu-bridged TiO2/porphyrin for enhanced photocatalytic hydrogen production, Applied Catalysis B: Environmental, 243 (2019) 1-9. [28] O. Mekasuwandumrong, N. Jantarasorn, J. Panpranot, M. Ratova, P. Kelly, P. Praserthdam, Synthesis of Cu/TiO2 catalysts by reactive magnetron sputtering deposition and its application for photocatalytic reduction of CO2 and H2O to CH4, Ceramics International, (2019). [29] N.T. Thanh Truc, T.-D. Pham, D. Van Thuan, L.T. Son, D.T. Tran, M.V. Nguyen,
V.N. Nguyen, N.M. Dang, H.T. Trang, Superior activity of Cu-NiWO4/g-C3N4 Z direct system for photocatalytic decomposition of VOCs in aerosol under visible light, Journal of Alloys and Compounds, 798 (2019) 12-18. [30] H. Terraschke, C. Wickleder, UV, Blue, Green, Yellow, Red, and Small: Newest Developments on Eu2+-Doped Nanophosphors, Chemical Reviews, 115 (2015) 11352-11378. [31] O. Hai, E. Yang, Q. Ren, X. Wu, Y, Han. Y, Zhao. J, Zhu. Plasma effect: A simple method for improving the persistent luminescence and light response range of persistent luminescent materials. Journal of luminescence, 2020.
Highlights [1] The plasma effect of Cu is applied to long afterglow materials. [2] The effect mechanism of Cu in Sr2MgSi2O7:Eu2+, Dy3+ was discussed. [3] A new method is provided to enhance the persistent luminescence performance.
Dear Editors, We submit our manuscript entitled “Enhancement of the persistent luminescence of Sr2MgSi2O7:Eu2+,Dy3+ by Cu nanoparticles” to “Journal of Luminescence” for publication. No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. We deeply appreciate your review for our manuscript, and we look forward to receiving comments. If you have any queries, please don’t hesitate to contact us. Thank you and best regards. Corresponding author: Enlong Y E-mail: [email protected]
Conflict of Interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled. Ou Hai, Enlong Y
2+ 3+ ,Dy by Cu
Ou Hai, Enlong Yang, Qiang Ren, Xiulan Wu, Yuhan Ren, Yujing Zhao, Jianfeng Zhu PII:
S0022-2313(19)31635-7
DOI:
https://doi.org/10.1016/j.jlumin.2019.116965
Reference:
LUMIN 116965
To appear in:
Journal of Luminescence
Received Date: 20 August 2019 Revised Date:
11 December 2019
Accepted Date: 11 December 2019
Please cite this article as: O. Hai, E. Yang, Q. Ren, X. Wu, Y. Ren, Y. Zhao, J. Zhu, Enhancement of 2+ 3+ the persistent luminescence of Sr2MgSi2O7:Eu ,Dy by Cu nanoparticles, Journal of Luminescence (2020), doi: https://doi.org/10.1016/j.jlumin.2019.116965. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier B.V.
Enhancement of the persistent luminescence of Sr2MgSi2O7:Eu2+,Dy3+ by Cu nanoparticles Ou Hai*, Enlong Yang*, Qiang Ren, Xiulan Wu, Yuhan Ren, Yujing Zhao, Jianfeng Zhu 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 Abstract: The persistent luminescence (PersL) phosphors are excellent energy-saving and environment-friendly materials. Here, Cu nanoparticles(CuNP) were deposited on the surface of Sr2MgSi2O7:Eu2+,Dy3+ (SMS) in the CuCl2 solution by photo-reduction deposition method for the first time, the initial brightness increases 1.1 times and the light response ranges are broadened to visible light. With the increasing of CuCl2 concentration, the PersL intensity of SMS increases to its maximum and then decreases, reaches the best at 0.3mmol/L CuCl2 solution. The changes of PersL intensity and absorption intensity indicate that CuNP can produce plasma effect (PE) on the surface of SMS, which efficiently increase the number of photo-generated electrons and holes, results more electrons can be trapped. For long afterglow materials, more electrons are captured by traps means that more electrons can be released to produce afterglow after remove the external light, thereby the PersL performance are effectively improved. In this paper, we used a simple method to improve the PersL performance of SMS and discussed the influence mechanism of *Corresponding author. Tel:8615091890116; 8613119136072; Email address: [email protected](O. Hai); [email protected](Enlong. Y).
CuNP in SMS. This result is attributed to the unique luminescence mechanism of long afterglow materials and the PE of CuNP. Our researches promote the application of SMS and provide a strategy for improving PersL of various long afterglow materials. Keywords:
Persistent
luminescence;
Cu
nanoparticles;
Plasmon
effect;
Photoluminescence; Afterglow phosphors 1. Introduction Long afterglow luminescence material, also called long phosphor powder, is an important energy-saving and environmental material. As a kind of excellent energy storage materials, long afterglow materials can store light energy and gradually release from several minutes to hours after being excited [1]. Nowadays, this material has been widely used in some field, such as traffic, safety, medical, electrical appliances and information storage [2-6]. Furthermore, it is reported to be a new photocatalysis material [7]. Silicates doped with the rare earth elements have been reported as a new kind of afterglow materials. The Eu2+ and Dy3+ co-dope Sr2MgSi2O7:Eu2+,Dy3+(SMS) materials have good chemical stability, thermal stability and low cost, which has attracted the attention of many researches [8, 9]. But its PersL performance is less than aluminate systems. Currently, the main methods to improve the PersL are ion doping, change of the synthesis methods and so on [10-12]. However, these methods are complex and high cost. Therefore, it is still a challenge to improve the PersL of SMS. For long afterglow materials, there are electrons and holes in the luminescence center. The excited electrons can be captured by the traps inside the materials when the material excited by the light source and the recombination of
electrons and holes can produce visible light after the excitation stops [8, 13]. In recent years, due to its unique optical properties, the PE of metals nanoparticles has been widely studied, such as photocatalysis and plasma-enhanced fluorescence [14-17]. In the photocatalysis filed, it has been proved that the PE produce by CuNP can promote the separation of electrons and holes for photocatalysis materials and result in more electrons available [18, 19]. In other words, the mobility of electrons can be increased by CuNP. However, for long afterglow materials, the study of PE enhancing PersL is weak relatively and the enhancement mechanism of PE is also rarely reported. In this paper, we took SMS as the research object. CuNP were deposited on the surface of SMS by traditional photo-reduction deposition method for the first time. The PE is achieved on the surface of SMS by controlling the deposition amounts of Cu, which can enhance the PersL performance and broaden the light response range of SMS. Furthermore, with the amounts of Cu deposition increase, the PersL intensity first increases and then decreases, reaching the best at 0.3mmol/L CuCl2 concentration. The initial brightness of SMS was increased by a factor of 1.1 at 0.3mmol/L CuCl2 concentration. In this paper, we provide a method for enhancing of the PersL and discuss the enhancement mechanism of Cu through the luminescence characteristic of long afterglow materials.
2. Experiments and measurements 2.1 Synthesis of SrMgSi2O7:Eu2+,Dy3+ Polycrystalline
powders
Sr1.96MgSi2O7:0.02Eu2+,0.02Dy3+(SMS)
were
synthesized via high-temperature solid-state synthesis according to the starting reagents:SrCO3(AR),
MgO(AR),
SiO2(AR),
H3BO3(AR),
Eu2O3(99.99%)
Dy2O3(99.9%) from Sinopharm Chemical Reagent Co., Ltd. (China). Additionally, 3mol% H3BO3 was added as flux. The reacted product was sintered at a temperature of 1240 3
, holding time is 2h, the heating rate is 5
/min, and then cooled at a rate of
/min. The entire sintering process was carried out in reducing gas flow
(10at.%H2+90at.%Ar). Then sample was added to the alcohol and was washed for 30minutes in ultrasonic wave. Finally, samples were obtained for the experiment. 2.2 Synthesis of Cu/SrMgSi2O7:Eu2+,Dy3+ The
Cu/SrMgSi2O7:Eu2+,Dy3+(Cu/SMS)
were
synthesized
through
the
photo-reduction deposition method. The brief experimental steps are shown in Fig.1. 1g SMS and 10ml various mole concentration of CuCl2 solutions (0.2, 0.25, 0.30, 0.35, 0.5, and 1.5mmol/L) were mixed in the light reactor. 100ml deionized water were added to the above reactor and the mixed solution was stirred in the dark for 10min to achieve pre-adsorption. A 250w uv light with main wavelength of 365nm was used as a reducing light. The mixture was reduced for 30min in an ultrasound apparatus and the Cu2+ was reduced into zerovalent Cu. The mixtures were then dried in a vacuum oven at 80˚C and were labeled as Cu/SMS-1, Cu/SMS-2, Cu/SMS-3, Cu/SMS-4, Cu/SMS-5 and Cu/SMS-6 respectively. Finally, we got the samples with different amounts of Cu deposition.
Fig.1. The flow chart of photo-reduction deposition method for Cu/SMS preparation. 2.3 Measurements The samples were characterized by X-ray powder diffraction (Rigaku D/Max-2200 type, Japan) with Cu Kα radiation (λ=1.5406Å). The surface morphologies of the samples were observed by scanning (FESEM, FEI . Verious 460, American)
and
transmission
electron
microscopy(TEM;
FEI
Tecnai
G2
hight-resolution transmission electron microscope). The uv-vis diffuse-reflection spectra were obtained on a uv-vis-near-IR spectrometer (Edinburgh FS5). The PL spectra were measured by the Hitachi F4600 Fluorescence spectrometer. The persistent luminescence curves were obtained by a PersL material optical test system using an artificial light as a light source with the irradiation time of 10min. All of the above measurements were taken at room temperature. 3. Results and discussion 3.1 Structure and Morphology of SMS and Cu/SMS The SMS was synthesized by high temperature solid state reaction method at
1240 . The XRD pattern (Fig. 2(a)) shows that the initial sample have a pure diffraction peaks, all of which are indexed to tetragonal Sr2MgSiO7 structure (space group:P-421m,No,113,JCPDS card: 75-1736). This indicates that the crystal structure of the host material was not changed by doped Eu2+ and Dy3+. Fig. 2(b) shows that the shape of SMS is blocky and the surface is smooth with no impurities attached, which provides an advantage for Cu deposition. The photoluminescence (PL) spectrum of SMS is shown in Fig. 2(c) with the excitation and emission are located at 361nm and 465nm respectively, which belongs to the characteristic peak of Eu2+ doped in the Sr2MgSi2O7 matrix [11, 12]. As shown in Fig. 2(d), the final material has a good PersL, which is attributed to a suitable trap depth produced by the introduction of Dy3+ [20].
Fig.2. (a) The XRD pattern of SMS; (b) The SEM image of SMS; (c) The excitation and emission spectrums of SMS; (d) The PersL curve of SMS. Fig. 3(a) and (b) shows the TEM images of SMS without Cu and Cu/SMS-3 respectively. It can be seen from Fig. 3(b) that after treatment with CuCl2 solution, many black particles distribute on the surface of SMS. Fig. 3(c) and (d) display the TEM images of Cu/SMS-3 and the result shows that CuNP distribute on the surface of SMS evenly with the shape of spherical. In this study, the grain size and distribution of Cu particles have a great impact on the PersL performance. We made a measure for the grain size of CuNP and the distance between different CuNP. As shown in the inset bar chart, the diameter is about 3nm and the distance is about 4-5nm. According to previous reports, we can conclude that the shape of CuNP has a great impact on the experimental results, which will be further studied in our following work. In order to prove that different amounts of Cu were deposited on the surface of SMS, the energy dispersive X-ray spectroscopy (EDS) was used for elemental mapping. Fig. 4(a) and (b) show the SEM images of SMS and Cu/SMS-3. Fig. 4(c) shows the elemental O mapping image of Cu/SMS-3. Fig. 4(d), (e) and (f) shows the elemental Cu mapping images in Cu/SMS-1, Cu/SMS-3 and Cu/SMS-6 respectively, indicating that CuNP are deposited on the surface of SMS with different amounts. Furthermore, as can be seen in the Fig. 4(f), large amounts of Cu were deposited on the surface of the SMS and the color of the sample became blue significantly. As the amounts of Cu deposition increases, the absorption light area of SMS reduced gradually. For long persistence materials, the effective contact area between SMS and
light reduced, which partly affects the luminescence performance.
Fig. 3. (a) The TEM image of SMS; (b), (c) and (d) are the TEM images of Cu/SMS-3.
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 4. (a) and (b) are the SEM images of SMS and Cu/SMS-3 respectively; (c) The elemental O mapping image in Cu/SMS-3; (d), (e) and (f) are the elemental Ag mapping images in Cu/SMS-1, Cu/SMS-3 and Cu/SMS-6 respectively.
3.2 Chemical Composition of Cu/SMS To investigate the surface elemental composite and the valence state of Cu on the surface of SMS, XPS and AES analyses were used to characterize the Cu/SMS-3. Fig. 5(a) shows the full surface survey of Cu/SMS-3, which confirms the presence of various elements (O, Si, Sr, Mg and Cu) on the surface of SMS. The high resolution spectrums of O, Sr, Si and Mg in SMS are shown in Fig. 5(b), these peaks are assigned to 530eV, 132ev, 100ev and 1300ev respectively, indicating the sample has good crystallinity, which is agreement with previous reports [21]. Fig. 5(c) shows the high resolution spectrum of Cu2p2/3, the binding energy peak at 932.6eV, which indicates the possibility of Cu0 and Cu+ [19]. Combing with the auger electron spectrum of Cu(Fig. 5(d)), Cu0 was found on the surface of SMS with the binding
energy is 568.3ev, which can be confirmed by the previous research [22-24]. The results of XPS and AES analysis provide a favorable evidence for the existence of metallic Cu.
Fig.5. (a) The full spectrum of Cu/SMS-3; (b) The high resolution spectrums of O1s, Sr3d, Si2p and Mg1s respectively; (c) and (d) are the high resolution spectrum of Cu2p and the LMM Auger spectrum of Cu respectively.
3.3 Absorption spectra Fig. 6(a) shows the uv-vis absorption spectrum of SMS and Cu/SMS. Compared with the initial sample, the absorption intensity gradually increases with the increasing of Cu deposition amounts. To make it clear that Cu promotes the absorption of SMS, Fig. 6(b) shows the absorption of SMS, Cu/SMS-1 and Cu/SMS-6 respectively, and
we can see that the absorption of samples in uv region is significantly enhanced after Cu deposition. When the CuNP are excited, it can generate a PE and form an electrostatic field on the surface of the SMS, which effectively promotes the separation and transfer of electrons and holes in the luminescence center. More electrons are excited and captured by traps, resulting in an increase in the absorption intensity. This is consistent with the results of PersL.
Fig. 6. (a) The absorption spectrum of SMS and Cu/SMS; (b) The absorption spectrum of SMS, Cu/SMS-3 and Cu/SMS-6. 3.4 Photoluminescence(PL) performance Fig. 7(a) and (b) shows the excitation and emission spectra of SMS and Cu/SMS respectively. All samples were excited at 365nm and monitored at 468nm. The excitation range is mainly between 250nm and 450nm. The emission spectra of these phosphors have a broad band peak around 470nm, which is attributed to the electrical transitions 4f65d1→4f7 of Eu2+ [25]. Compared with the initial sample, deposition of Cu had no obvious effect on the position of the peak, but the intensities of the excitation and emission are obviously decreased. This is consistent with our expectation and the change of PL spectrums is attributed to the PE of CuNP. CuNP on
the surface of SMS allows more photo-generated electrons to be transferred and then captured, reducing recombination rate of electrons and holes. More electrons are captured by traps, resulting in lower emission spectra.
Fig. 7. (a) and (b) are the excitation and emission spectra of SMS and Cu/SMS respectively. 3.5 The persistent luminescence curves After removing the excitation light source, the change of afterglow luminescence with the time is called PersL performance. All samples were excited under 25W uv lamp for 10 minutes. Fig. 8(a) presents the afterglow decay curves of the SMS and Cu/SMS. Obviously, appropriate amounts of Cu deposition can improve the PersL of SMS. When the CuCl2 concentration is 0.3mmol/L, the PersL performance is the best, and the initial luminescence increased by 1.1 times. Fig. 8(b) shows the PersL curves of SMS and Cu/SMS-3 within 30min, and the luminescence intensity of Cu/SMS-3 is significantly better than SMS. This is because CuNP produce PE after excited, which forms a near electrostatic filed on the surface of SMS, promoting the separation of electrons and holes. For long persistence luminescent materials, there are traps to capture electrons in the luminescent center [8]. When the excitation stops, the
recombination of the captured electrons and holes will produce afterglow. Due to the PE of Cu, the electrostatic filed produced by Cu promotes the separation of electrons and holes, so that more electrons are transferred and captured by traps, thus improves PersL performance. In order to accurately study the effect of different amounts of Cu deposition on the PerL of SMS, the luminescence intensity at 0min and 5min (Fig. 8(c)) show that with the increase of Cu amounts, the PersL performance increases to its maximum and then decreases, reaching the best in the 0.3mmol/L CuCl2 solution. However, with a large amount of Cu deposited on the surface of SMS, the PersL decreased gradually and lower than SMS. This may be because the amounts of Cu deposition are too much, which reduces the effective contact area between SMS and light and less light can reach the luminescence center. For long afterglow materials, different trap depth has great influence on the luminescence performance [4, 26]. In order to further study the effect of Cu on the depth of traps, we used the following equation to analyze the long afterglow curve [20]. I =Ic+A1exp(-t/τ1) + A2exp(-t/τ2)
(1)
where I is the luminescence intensity, t is the time, A1 and A2 are the constants, τ1 and τ2 are the decay constants, respectively. It is well known that τ1 and τ2 represents the fast and slow decay process respectively. It can be seen from the fitting results in Table1, as the concentration of CuCl2 solution increases, τ1 and τ2 decrease first and then increase. According to above conclusion, more electrons are captured due to the PE of Cu, which means that they are more likely to be released, so the proper Cu
reduce the depth of the trap. The normalized decay curves and the fitting process are shown in Fig. S1.
Fig. 8. (a) The PersL curves of SMS and Cu/SMS; (b) The PersL curves of SMS and Cu/SMS-3; (c) The luminescence intensity of SMS a0min and 5min.
Table 1 The fitting results of the decay curves treated by different CuCl2 concentration. CuCl2 (mmol/L)
τ1
τ2
0 0.2 0.25 0.3 0.35 0.8 1.5
9.21 6.55 6.16 5.43 5.91 6.25 4.91
92.94 67.96 64.30 59.98 59.86 66.91 43.98
3.6 The mechanism of Cu enhancing persistent luminescence performance As a kind of plasma material, CuNP can promote the separation and inhibit the recombination of photo-generated electrons and holes in semiconductor materials, which has been proved in photocatalysis field [14, 27-29]. In other words, the mobility of photo-generated electrons can be increased by PE of CuNP. For SMS, there are free electrons and traps in the luminescence center and these electrons can be captured by traps after being excited. However, according previous studies, the emission mechanism of long afterglow material is still debatable [9, 12]. Here, the emission mechanism of SMS and the enhancement mechanism of Cu are proposed as follows (Fig. 9). When electrons in the ground state 4f of Eu2+ are excited to the energy level of 5d, some of them return to the grate state forming a unique emission of Eu2+ [30]. Another part are transferred to the conduction band and captured by traps(Vo" or DySr ) of SMS (The path is represented by a solid black line). Meanwhile, Eu2+ becomes Eu3+, and Dy3+ becomes Dy2+, which can be confirmed from previous reports [21]. After the external light source is removed, these captured
electrons are released and recombined with Eu2+ to produce PersL (The path is represented by a red dotted line). As shown in Fig. 9, When the Cu/SMS excited by the light, the luminescence center of SMS can generate the separation of electrons and holes. At the same time, CuNP can produce PE, which produces an electrostatic field on the surface of SMS [31]. Under an external electrostatic field, these excited electrons are more easily separated, transferred and captured by traps. This indicates that more electrons are captured by traps than that in the absence of electrostatic field. For long afterglow materials, more electrons are captured by traps means that more electrons can be released after remove the external light, thus results in a better PersL.
Fig.9. The Schematic diagram of Cu enhancing PersL performance, the purple sphere is SMS, the green sphere is Cu nanoparticles, the black dotted line represents the plasma enhancement effect. 4. Conclusions In summary, Cu/SMS phosphors with varying amounts of Cu deposition were
synthesized by a simple method. XPS and AES confirmed the presence of Cu0 on the surface of SMS. The PersL intensity is effectively improved and the initial brightness is increased by 1.1 times in 0.3mm/L CuCl2 solution. The light response range of SMS is broadened to visible light after Cu deposited. With the number of captured electrons and holes increasing, they are more likely to be released, thus reduce the depth of the trap. The improvement of PersL performance is attributed to the unique luminescence mechanism of SMS and PE of Cu. Our researches promote the application of long afterglow materials and provide a strategy to enhance the PersL performance for various afterglow materials. Acknowledgements This work was financially supported by Natural Science Foundation of Shaanxi Province (Grant No. 2019JQ-785), 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). References: [1] Y. Li, M. Gecevicius, J. Qiu, Long persistent phosphors—from fundamentals to applications, Chemical Society Reviews, 45 (2016) 2090-2136. [2] O. Hai, H. Jiang, Q. Zhang, Q. Ren, X. Wu, J. Hu, Effect of cooling rate on the microstructure and luminescence properties of Sr2MgSi2O7:Eu(2+),Dy(3+) materials, Luminescence:the journal of biological and chemical luminescence, 32(2017) 1442-1447.
[3] M.A. Tshabalala, H.C. Swart, F.B. Dejene, E. Coetsee, O.M. Ntwaeaborwa, Structure, surface analysis, photoluminescent properties and decay characteristics of Tb3+-Eu3+ co-activated Sr2MgSi2O7 phosphor, Applied Surface Science, 360 (2016) 409-418. [4] J. Ueda, S. Miyano, S. Tanabe, Formation of Deep Electron Traps by Yb(3+) Codoping Leads to Super-Long Persistent Luminescence in Ce(3+)-Doped Yttrium Aluminum Gallium Garnet Phosphors, ACS Appl Mater Interfaces, 10 (2018) 20652-20660. [5] H. Wu, Y. Hu, B. Zeng, Z. Mou, L. Deng, Tunable luminescent properties by adjusting the Sr/Ba ratio in Sr1.97−xBaxMgSi2O7:Eu2+0.01,Dy3+0.02 phosphors, Journal of Physics and Chemistry of Solids, 72 (2011) 1284-1289. [6] Y. Zhuang, Y. Lv, L. Wang, W. Chen, T.L. Zhou, T. Takeda, N. Hirosaki, R.J. Xie, Trap Depth Engineering of SrSi2O2N2:Ln(2+),Ln(3+) (Ln(2+) = Yb, Eu; Ln(3+) = Dy, Ho,Er) Persistent Luminescence Materials for Information Storage Applications, ACS Appl Mater Interfaces, 10 (2018) 1854-1864. [7] G Cui, X Yang, Y Zhang, Y Fan, P Chen, H Cui, Y Liu, X Shi, Q Shang, B Tang. Round-the-clock photocatalytic hydrogen production with high efficiency by a long afterglow
material[J].
Angewandte
Chemie
International
Edition,
58(2019):1340-1344. [8] O. Hai, Q. Ren, X. Wu, Q. Zhang, Z. Zhang, Z. Zhang, Insights into the element gradient in the grain and luminescence mechanism of the long afterglow material Sr2MgSi2O7:Eu2+,Dy3+, Journal of Alloys and Compounds, 779 (2019) 892-899.
[9] O. Hai, Z. zhang, Q. Ren, X. Wu, Q. Zhang, B. Zeng, D. Li, The preparation and functional studies of the porous long afterglow luminescent materials, Dyes and Pigments, 156 (2018) 160-166. [10] E. Finley, A. Cobb, A. Duke, A. Paterson, J. Brgoch, Optimizing Blue Persistent Luminescence in (Sr1−δBaδ)2MgSi2O7:Eu2+,Dy3+ via Solid Solution for Use in Point-of-Care Diagnostics, ACS Applied Materials & Interfaces, 8 (2016) 26956-26963. [11] H. Wu, Y. Hu, Y. Wang, C. Fu, Influence on the luminescence properties of the lattice defects in Sr2MgSi2O7:Eu2+,M (M=Dy3+,La3+ or Na1+), Journal of Alloys and Compounds, 497 (2010) 330-335. [12] L. Xiao, J. Zhou, G. Liu, L. Wang, Luminescent properties of R+ doped Sr2MgSi2O7:Eu2+,Dy3+(R+ = Li+, Ag+) phosphors, Journal of Alloys and Compounds, 712 (2017) 24-29. [13] B. Liu, C. Shi, M. Yin, L. Dong, Z. Xiao, The trap states in the Sr2MgSi2O7 and (Sr,Ca)MgSi2O7 long afterglow phosphor activated by Eu2+ and Dy3+, Journal of Alloys and Compounds, 387 (2005) 65-69. [14] S. Chen, X. Li, W. Zhou, S. Zhang, Y. Fang, Carbon-coated Cu-TiO2 nanocomposite with enhanced photostability and photocatalytic activity, Applied Surface Science, 466 (2019) 254-261. [15] Y. Gan, M. Zhang, J. Xiong, J. Zhu, W. Li, C. Zhang, G. Cheng, Impact of Cu particles on adsorption and photocatalytic capability of mesoporous Cu@TiO2 hybrid towards ciprofloxacin antibiotic removal, Journal of the Taiwan Institute of Chemical
Engineers, 96 (2019) 229-242. [16] W. Ye, Q. Huang, X. Jiao, X. Liu, G. Hu, Plasmon-enhanced fluorescence of CaF 2:Eu
2+
nanocrystals by Ag nanoparticles, Journal of Alloys and Compounds, 719
(2017) 159-170. [17] B. Zhang, Y. Chen, J. Li, E. Pippel, H. Yang, Z. Gao, Y. Qin, High Efficiency Cu-ZnO Hydrogenation Catalyst: The Tailoring of Cu-ZnO Interface Sites by Molecular Layer Deposition, ACS Catalysis, 5 (2015) 5567-5573. [18] P.K. Baruah, A.K. Sharma, A. Khare, Effective control of particle size, surface plasmon resonance and stoichiometry of Cu@CuxO nanoparticles synthesized by laser ablation of Cu in distilled water, Optics & Laser Technology, 108 (2018) 574-582. [19] J. Qiu, N.E. Richey, J.S. DuChene, Y. Zhai, Y. Zhang, L. McElwee-White, W.D. Wei, Surface Plasmon-Mediated Chemical Solution Deposition of Cu Nanoparticle Films, The Journal of Physical Chemistry C, 120 (2016) 20775-20780. [20] H. Wu, Y. Hu, Y. Wang, B. Zeng, Z. Mou, L. Deng, W. Xie, Influence on luminescent properties of the Sr2MgSi2O7:Eu2+ by Dy3+,Nd3+ co-doping, Journal of Alloys and Compounds, 486 (2009) 549-553. [21] G Cui, X Yang, Y Zhang, Y Fan, P Chen, H Cui, Y Liu, X Shi, Q Shang, B Tang. Round-the-clock photocatalytic hydrogen production with high efficiency by a long afterglow
material[J].
Angewandte
Chemie
International
Edition,
58(2019):1340-1344.. [22] T. Ghodselahi, H. Zahrabi, M.H. Saani, M.A. Vesaghi, CO Gas Sensor Properties
of Cu@CuO Core–Shell Nanoparticles Based on Localized Surface Plasmon Resonance, The Journal of Physical Chemistry C, 115 (2011) 22126-22130. [23] J. Gong, H. Yue, Y. Zhao, S. Zhao, L. Zhao, J. Lv, S. Wang, X. Ma, Synthesis of ethanol via syngas on Cu/SiO2 catalysts with balanced Cu0-Cu+ sites, J Am Chem Soc, 134 (2012) 13922-13925. [24] J. Hernandez, P. Wrschka, G.S. Oehrlein, Surface Chemistry Studies of Copper Chemical Mechanical Planarization, Journal of The Electrochemical Society, 148 (2001) G389. [25] R. Shrivastava, J. Kaur, Characterisation and Mechanoluminescence studies of Sr2MgSi2O7:Eu2+,Dy3+, Journal of Radiation Research and Applied Sciences, 8 (2019) 201-207. [26] E. Finley, A. Mansouri Tehrani, J. Brgoch, Intrinsic Defects Drive Persistent Luminescence in Monoclinic SrAl2O4:Eu2+, The Journal of Physical Chemistry C, 122 (2018) 16309-16314. [27] X. Guo, X. Li, L. Qin, S.-Z. Kang, G. Li, A highly active nano-micro hybrid derived from Cu-bridged TiO2/porphyrin for enhanced photocatalytic hydrogen production, Applied Catalysis B: Environmental, 243 (2019) 1-9. [28] O. Mekasuwandumrong, N. Jantarasorn, J. Panpranot, M. Ratova, P. Kelly, P. Praserthdam, Synthesis of Cu/TiO2 catalysts by reactive magnetron sputtering deposition and its application for photocatalytic reduction of CO2 and H2O to CH4, Ceramics International, (2019). [29] N.T. Thanh Truc, T.-D. Pham, D. Van Thuan, L.T. Son, D.T. Tran, M.V. Nguyen,
V.N. Nguyen, N.M. Dang, H.T. Trang, Superior activity of Cu-NiWO4/g-C3N4 Z direct system for photocatalytic decomposition of VOCs in aerosol under visible light, Journal of Alloys and Compounds, 798 (2019) 12-18. [30] H. Terraschke, C. Wickleder, UV, Blue, Green, Yellow, Red, and Small: Newest Developments on Eu2+-Doped Nanophosphors, Chemical Reviews, 115 (2015) 11352-11378. [31] O. Hai, E. Yang, Q. Ren, X. Wu, Y, Han. Y, Zhao. J, Zhu. Plasma effect: A simple method for improving the persistent luminescence and light response range of persistent luminescent materials. Journal of luminescence, 2020.
Highlights [1] The plasma effect of Cu is applied to long afterglow materials. [2] The effect mechanism of Cu in Sr2MgSi2O7:Eu2+, Dy3+ was discussed. [3] A new method is provided to enhance the persistent luminescence performance.
Dear Editors, We submit our manuscript entitled “Enhancement of the persistent luminescence of Sr2MgSi2O7:Eu2+,Dy3+ by Cu nanoparticles” to “Journal of Luminescence” for publication. No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. We deeply appreciate your review for our manuscript, and we look forward to receiving comments. If you have any queries, please don’t hesitate to contact us. Thank you and best regards. Corresponding author: Enlong Y E-mail: [email protected]
Conflict of Interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled. Ou Hai, Enlong Y