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Yb3+ tri-doped oxyfluoride glasses for glass greenhouse
Optical Materials 62 (2016) 494e498
Contents lists available at ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Broadband emission from Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses for glass greenhouse Weirong Wang a, b, Zhangyu Huang a, b, Huiping Gao a, b, Xiuying Cheng a, **, Yanli Mao a, b, * a b
School of Physics and Electronics, Henan University, Kaifeng 475004, China Institute for Computational Materials Science, Henan University, Kaifeng 475004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 February 2016 Received in revised form 16 October 2016 Accepted 19 October 2016
In this work, a kind of oxyfluoride glasses tri-doped with Ce3þ/Mn2þ/Yb3þ ions was prepared by a simple and fast high temperature melting method. Under excitation with 300 nm light, two meaningful broad band emissions (ranged from 340 to 500 nm and 510e700 nm) were obtained, which matched well with the absorption of the chlorophylls. Under near-infrared (980 nm) excitation, an abnormal up-conversion luminescence was demonstrated in the oxyfluoride glasses by the energy transfer from Yb3þ to Mn2þ. In addition, the up-conversion emission has a red shift along with the increase of the doping concentration of Mn2þ, which would contribute to match the action spectrum of photosynthesis better. Our materials will be favored to extend the utilization of solar energy in glass greenhouse for plant cultivation. © 2016 Elsevier B.V. All rights reserved.
Keywords: Oxyfluoride glasses Ce3þ/Mn2þ/Yb3þ Down-conversion Up-conversion Glass greenhouse
1. Introduction Currently, a fast-growing interest has been witnessed on the approaches to improve the photosynthesis of the green plants [1e5]. As one of significant parameters for plant growth, light is not only the energy source of greenery photosynthesis, but also the power source of sprout, blossom, and fruit as well as other morphogenesis for plants. Therefore, the light quality for plants plays a significant role on the harvest. The main light bands absorbed by chlorophyll of greenery are reddish orange (600e700 nm) and bluish violet (400e480 nm) lights, which is only a small percentage of the whole solar spectrum. Longer wavelengths can hardly been absorbed by chlorophylls and other photosynthetic antenna pigments, while the ultraviolet (UV) in the sunlight are even harmful to the plant. Therefore, it is meaningful to convert the useless sunlight to reddish-orange and bluish violet light for improving the utilization level of solar light in the process of photosynthesis.
* Corresponding author. School of Physics and Electronics, Henan University, Kaifeng 475004, China. ** Corresponding author. School of Physics and Electronics, Henan University, Kaifeng 475004, China. E-mail addresses: [email protected] (X. Cheng), [email protected] (Y. Mao). http://dx.doi.org/10.1016/j.optmat.2016.10.037 0925-3467/© 2016 Elsevier B.V. All rights reserved.
In order to promote the growth and achieve higher yields of the crops, many kinds of methods have been studied and used in the past years. Notably, the use of plastic greenhouses in lowtemperature seasons has attracted considerable attention. However, there are still many shortcomings of plastic greenhouse, such as short service lifetime, toxicity to the environment, and chemical instability [6e9]. To solve these problems, the glass greenhouses which show superior performance to the traditional plastic greenhouses in many respects have attracted widely attention [6e9]. The glass materials have better stability against ultraviolet irradiation, better thermal retardation, and excellent chemical durability which directly determines a long service life. Moreover, lanthanide-doped transparent materials have wonderful luminous traits in the UV, visible (Vis) and near-infrared (NIR) wavelength regions [5e18]. Hence, the predominant properties of rare earth doped transparent glass materials allow them to realize promising applications in greenhouses. Recently, solar spectral conversion phosphor has been embedded within a specific reactor device [5,6]. It is experimentally demonstrated that the tune of useless green photons to red can greatly improve the energy harvesting of chlorophylls. However, the complex assembly process and high cost may hinder the development of the device for its large-scale production and application. The solar spectral conversion glass greenhouse can be a
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suitable substitution, for it can be easily assembled and constructed like traditional glass greenhouses. Beneficially, the glass material exhibits excellent resistance to water and corrosion. It is known that the down-conversion (DC) glass material shows an excellent optical performance which is favorable to convert more violet and green photons to red ones via rare-earth or transition-metal ions co-doped in transparent phosphate glasses [7e9]. Likewise, the light use efficiency of photosynthetic systems would also be greatly improved if photosynthesis could use NIR radiation. Therefore, an ability to simultaneously use UV and NIR radiation would a more potential approach to improve the efficiency of photosynthesis. In the previous works, we have studied the Ce3þ/Er3þ/Yb3þ tridoped oxyfluoride glass ceramics for glass greenhouses [11]. The glasses are highly transparent in the visible light range and own intense absorption in the UV and NIR wavelength region. Especially, the glasses can transfer ultraviolet and part of NIR into reddish orange light. However, the emission region of the red light is not broad enough. In addition, the energy transfer between the Ce3þ to Er3þ ions is not very effective. This will result in a poor utilization rate of the materials to sunlight. Hence, the material which not only shows a wider region of excitation but also exhibits a broad emission of bluish violet and reddish orange light is still very promising. The emission of Mn2þ is based on the 4T1g(4G)/6A1g(6S) transition. By introducing an efficient sensitizer, the emission of Mn2þ can be considerably improved. At present, many Mn2þ/Ce3þ co-doped red luminescence materials have been studied, such as ZnS: Ce3þ, Mn2þ [19], Ca3Sc2Si3O12: Ce3þ, Mn2þ [20], MgY4Si3O13: Ce3þ, Mn2þ [21], and Ca4Si2O7F2: Ce3þ, Mn2þ [22] phosphors or Ce3þ/Mn2þ co-doped glass-ceramics containing b-Zn2SiO4 nanocrystals [23]. Furthermore, in order to obtain the broadband upconversion (UC) luminescence, Mn2þ/Yb3þ co-doped phosphors has also been reported and led to some new and unexpected results in the search for novel UC materials and process [24e27]. In this paper, we report the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses. The 50SiO2-20Al2O3-20CaF2-10NaF glasses were selected as the host materials because of its high transparency, lowmelting temperature, simple manufacturing procedure, and good solubility for Ce3þ/Mn2þ/Yb3þ ions. Among the glasses systems, the oxyfluoride glasses are expected to combine the advantages of high mechanical strength of oxide glasses and low phonon energy of fluoride glasses. This will be favored to the energy transfer between neighbor ions. With the broad band excitation of UVeVis and NIR 980 nm lights, a strong and broadband of reddish orange light has been obtained. Furthermore, the energy transfer mechanisms among Ce3þ/Mn2þ/Yb3þ of up and down conversion have also been revealed by detail analysis of the excitation, up and down conversion emission spectra, and the luminescent decay curves of the samples. 2. Experiment section The oxyfluoride glass samples with the compositions in mol% of 50SiO2-20Al2O3-20CaF2-10NaF (G): xCe3þ, yMn2þ, zYb3þ were prepared by high temperature melting method. The doped CeF3 and YbF3 content were fixed to x ¼ 0.1 mol% and z ¼ 5 mol%, while the MnCO3 content was y ¼ 0.1 mol%, 0.5 mol%, 1 mol%, and 1.5 mol % respectively. According to the doping concentration of Ce3þ, Mn2þ and Yb3þ ions, the samples would be denoted further in the text as G:0.1Ce3þ, G:1Mn2þ, G:0.1Ce1Mn, G:0.1Ce0.1Mn5Yb, G:0.1Ce0.5Mn5Yb, G: 0.1Ce1Mn5Yb and G:0.1Ce1.5Mn5Yb, respectively. For each batch, about 10 g raw materials including SiO2 (AR), Al2O3 (AR), CaF2 (AR), NaF (AR), CeF3 (99.9%), MnCO3 (99.9%), YbF3 (99.9%) were mixed thoroughly and then heated in a covered corundum crucible at 1350 C for 2 h to achieve a homogeneous melt, then the melt was cast into a copper mold to process
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quenching. The resulted glasses were kept at 300 C for 120 min in an annealing furnace to relinquish inner stress. The obtained samples were polished to optical quality. The photoluminescence (PL) and the photoluminescence excitation (PLE) spectra were measured by a Tau-3 fluorescence spectrophotometer (Jobin Yvon-Inc, France). Luminescence decay curves and the UC luminescence spectrums were measured with a FLS980E spectrometer (Edinburgh Instruments Ltd., UK). 3. Results and discussion The excitation and emission spectra of the Ce3þ or Mn2þ singly doped glass are shown in Fig. 1(a) and (b). As shown in Fig. 1(a), the PL spectrum of G:0.1Ce3þ displays a broad band extending from 340 to 500 nm, which can be attributed to the typical transition from 5d level to the ground state of Ce3þ. The excitation spectrum monitored at 362 nm shows a broad absorption band within the 250e350 nm UV range, which is due to 4f-5d transition of the Ce3þ. G:1Mn2þ presents a broad band emission centered at 585 nm under 410 nm excitation in Fig. 1(b), which corresponds to the 4 T1(G)/6A1(S) transition of Mn2þ. The excitation spectrum of G:1Mn2þ sample consists of two bands centered at 355 and 410 nm, which are assigned to the transitions from 6A1(S) to 4T2(D) and 4 T1(G) levels of Mn2þ, respectively. Obviously, there is a significant spectral overlap between the Ce3þ PL and Mn2þ PLE spectra as shown in Fig. 1(c), indicating the possibility of energy transfer from Ce3þ to Mn2þ in our oxyfluoride glasses. Fortunately, the assumption is confirmed by the PLE spectra of G:0.1Ce1Mn monitoring the board emission peaks at 585 nm. As shown in Fig. 1(d), three broad excitation bands of 350e500 nm and 250e350 nm can be observed, which respectively corresponding to the transitions from 6A1(S) to 4 T2(D) and 4T1(G) levels of Mn2þ and the 4f-5d transition of the Ce3þ. And it shows the existence of energy transfer from Ce3þ to Mn2þ. The down-conversion emission spectra (ranged from 360 to 680 nm) of the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses has been measured under excitation of 300 nm with a xenon lamp, and illustrated in Fig. 2. It is clearly noticed that all samples exhibit two broad emission band centered at 360 and 620 nm, corresponding to the emission of Ce3þ and Mn2þ, respectively. As the content of Mn2þ increases from 0.1% to 1.5 mol%, the shape and peak positions of the DC emission spectra show no obvious variation. However, the total DC emission intensity and the luminescence intensity distribution are changed largely. By comparing the intensity of Ce3þ ranged from 360 to 500 nm, a gradually decrease trend is showed along with the increase of the concentration of Mn2þ. In addition, the luminescence intensity of Mn2þ also shows a monotone increase along with the doping concentration of Mn2þ increasing from 0.1 to 1 mol%. Further increasing the Mn2þ ions doping concentration would result in emission intensity decrease due to the concentration quenching effect. Fig. 3 show that the decay curves of Ce3þ emission at 362 nm along with various Mn2þ concentrations doping, which corresponds to Ce3þ:5d-4f transition, upon excitation of Ce3þ at 300 nm. With the increase doping concentration of Mn2þ, the deviation from the exponential rule becomes more obvious. By calculation, the average lifetime of Ce3þ ions are found to be about 30.8, 28.2, 24.8, and 22.6 ns corresponding to the G:0.1Ce0.1Mn5Yb, G:0.1Ce0.5Mn5Yb, G:0.1Ce1Mn5Yb and G:0.1Ce1.5Mn5Yb, respectively. Apparently, the fluorescence lifetime of Ce3þ ions in the glass sample become shorter as the concentration of Mn2þ increasing, which is the clear evidence of energy transfer from Ce3þ to Mn2þ in this tri-doped glass systems. According to this DC energy transfer mechanism, the DC emission intensity of Mn2þ should mainly depend on the conversion
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Fig. 1. The excitation and emission spectra of (a) 0.1 mol% Ce3þ -doped glass; (b) 1 mol% Mn2þ -doped glass; (c) spectral overlap between the excitation spectrum for Ce3þ doped glass and emission spectrum for Mn2þ doped glass; (d) The broad excitation spectra of Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses, monitoring at 585 nm.
Fig. 2. The DC emission spectra of the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses as a function of Mn2þ concentration.
efficiency of Ce3þ (from 300 to 360 nm) and the energy transfer rate from Ce3þ to Mn2þ. In all of our samples, the doping concentration of Ce3þ is a constant value of 0.1 mol%, hence, the conversion efficiencies of Ce3þ of all the samples are the same. The energy transfer rate from Ce3þ to Mn2þ depends on the distance between the two ions. From this point of view, the emission intensity of Mn2þ will increase when reducing the distance by increasing Mn2þ concentration into the sample. However, considering the concentration quenching effect, the emission intensity of Mn2þ will decrease when excessive activator ions are doped in to the sample. Therefore, a variation of total DC emission intensity and the luminescence intensity distribution appears, as shown in Fig. 2. Fig. 4 (a) shows the NIR to Vis up-conversion emission spectra of G:0.1Ce0.1Mn5Yb, G:0.1Ce0.5Mn5Yb, G:0.1Ce1Mn5Yb and G:0.1Ce1.5Mn5Yb samples under excitation at 980 nm. The abnormal visible UC emission of Mn2þ is observed in the Ce3þ/ Mn2þ/Yb3þ tri-doped oxyfluoride glasses systems. Moreover, all UC
Fig. 3. The luminescent decay curves of Ce3þ emission at 361 nm by excitation of at 300 nm with various Mn2þ concentration.
spectra exhibit a broad emission band ranging from 510 to 700 nm with a single peak which corresponding to Mn2þ:4T1/6A1. Meanwhile, a monotonically enhancement trend of the UC luminescence intensity with the increase doping concentration of Mn2þ is evidently showed in Fig. 4(b). This increasing phenomenon could be attributed to the increased number of luminescent active ions (Mn2þ ions). It is also indicated that 1.5 mol% is still an appropriate concentration of Mn2þ ions for emission in UC process although a quenching has happened in the down-conversion process. Furthermore, with the increasing variation of the content of Mn2þ, an obvious red shift of UC luminescence can also be found in Fig. 4(a) from 560 to 620 nm with about 20 nm interval linear growth. This is a good sign, as it can make the UC luminescence spectrum match better with the absorption spectrum of
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Fig. 4. (a) UC emission spectra and (b) Mn2þ emission intensities of the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses as a function of Mn2þ concentration.
chlorophyll. Hence, it can be feasible to use as our photo-converting material for promoting the growth of plants. According to the above results, a most possible UC energy transfer mechanism between Mn2þ/Yb3þ can be proposed, as schematically illustrated in Fig. 5. At first, a small quantity of Mn2þ (0.1 mol%) was doped into the oxyfluoride glass system. On account of the existence of Yb3þ, a dimer of Yb3þ-Mn2þ will form. Under excitation by a 980 nm laser diode, a visible green emission centered at 560 nm can be seen and detected via two kinds of corresponding ground state absorption (GSA) and excited state absorption (ESA) UC mechanism, as shown in Fig. 5. Because Mn2þ ions have no intermediate excitation states resonant with Yb3þ ions, the GSA/ESA cannot occur simultaneously in single Yb3þ or Mn2þ. So both Yb3þ and Mn2þ ions should be involved in the UC mechanism. When two Yb3þ ions combine their excitation energy by a cooperative process to transfer it to the nearby Mn2þ (or Mn2þ pairs) simultaneously, then they will gives the red (or green) emission [27,28]. When adding more Mn2þ into the system, more Yb3þ-Mn2þ dimers (or even Yb3þ-Mn2þ-Mn2þ trimer) will form. The distance between Yb3þand Mn2þ may also reduced, which will
result in an increased energy transfer rate from Yb3þ to Mn2þ. Additionally, as more Mn2þ adding in to the glass system, the size of the Yb3þ-Mn2þ dimer will become larger as well, according to the size effect, a red shift UC luminescence appears. [24,28e30]. It is known that the solar radiation onto the earth's surface has wavelengths ranging from about 200 nm for ultraviolet radiation to about 2500 nm for infrared radiation. However, the radiation in the 200e280 nm wavelength region (also called the solar blind region) of solar spectrum could hardly reach the surface of the earth because nearly all of them are absorbed by ozonosphere existing in the upper atmosphere. The solar radiation spectrum in the 280e1800 nm wavelength region was showed in Fig. 6. The UV wavelength light of 280e400 nm cannot be absorbed by plants and even does harm to plants. Hence, it is significant to realize the conversion of this part of the solar light into useful light for plant. Herein, we prepared tri-doped Ce3þ/Mn2þ/Yb3þ oxyfluoride glasses which showed an outstanding transparency, as shown in the insert picture of Fig. 6. Ce3þ is known as an effective conversion ions to realize the conversion of light from ultraviolet (280e400 nm) to blue-violet (340e500 nm), which precisely match the absorption of
Fig. 5. Schematic representation of the proposed UC mechanism in the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses.
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Acknowledgements This work is supported by Science and Technology Research Project of Henan Province (No. 142102210389), the National Natural Science Foundation of China (Grant No. 21103043), The Program for Science and Technology Innovation Talents in Universities of Henan Province (No.16HASTIT043) and the Program for Innovative Research Team (in Science and Technology) in University of Henan Province (No. 13IRTSTHN017).
References
Fig. 6. Solar radiation spectrum in the 280e1800 nm wavelength region. The inset shows the picture of the samples with 0.1 mol% and 1 mol% of Mn2þ of the Ce3þ/Mn2þ/ Yb3þ tri-doped oxyfluoride glasses.
chlorophyll. Moreover, a confirmed energy transfer process from Ce3þ to Mn2þ can also improve the emission of Mn2þ, due to the high absorption coefficient of Ce3þ. In addition, a broad band emission ranging from 510 to 700 nm of Mn2þ ions also match well of the red region absorption of chlorophyll. Therefore, an effective convertor for photosynthesis luminescence conversion can be obtained via DC energy transfer process. Additionally, a rare UC energy transfer process from Yb3þ to Mn2þ has also been found, which is an another route to get a broad reddish orange light. This will improve the utilization of the NIR light of sunlight for green plant photosynthesis. Thus, it is indicated that the material will have a great application prospect in use of greenhouse. 4. Conclusions In summary, the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses have been synthesized. In our glasses system, Ce3þ exhibits an intense UV-blue emission in the range of 340e500 nm. Meanwhile, Mn2þ shows an intense red emission band peaked at 585 nm due to the effective energy transfer from Ce3þ to Mn2þ ions. Furthermore, an efficient broadband UC luminescence upon 980 nm laser excitation was also investigated systematically. These glasses have broad band excitation, and can simultaneously convert the UVeVis and NIR lights into bluish violet and red lights, which is beneficial to the photosynthesis of the green plants. The down-converting and up-converting materials can enrich the action spectrum of photosynthesis in the UV, Vis and NIR range. Thus, our oxyfluoride glasses can be applied to the glass greenhouse for improving the photosynthesis of the green plants.
[1] X.G. Zhu, S.P. Long, D.R. Ort, Annu. Rev. Plant Biol. 61 (2010) 235e261. [2] A. Graf, A.M. Smith, Trends Plant Sci. 16 (3) (2011) 169e175. [3] R.E. Nlankenship, D.M. Tiede, J. Barber, G.W. Brudvig, G. Fleming, M. Ghirardi, Science 332 (2011) 805. €rvi, J. Ho € lsa €, E. Tyystj€ [4] T. Antal, E. Harju, L. Pihlgren, M. Lastusaari, T. Tyystja arvi, Int. J. Hydrogen Energy 37 (2012) 8859e8863. [5] L. Wondraczek, M. Batenschuk, M.A. Schmidt, R. Borchardt, S. Scheiner, B. Seemann, P. Scheizer, C.J. Brabec, Nat. Commun. 4 (2013). No. Art. no. 2047. [6] Q. Xia, M. Batentschuk, A. Osvet, P. Richter, D.-P. H€ ader, J. Schneider, C.J. Brabec, L. Wondraczek, A. Winnacker, Opt. Exp. 21 (2013) A909. [7] C.G. Ming, F. Song, L.Q. An, X.B. Ren, Appl. Phys. Lett. 102 (2013) 14903. [8] C.G. Ming, F. Song, X.B. Ren, L.Q. An, Appl. Phys. Lett. 103 (2013) 041906. [9] Y.D. Han, F. Song, Q. Li, F.X. Wang, C.G. Ming, J.G. Tian, Opt. Mater. 37 (2014) 756e759. [10] T.H. Lv, X.H. Xu, X. Yu, D. Zhou, J. Qiu, Ceram. Int. 41 (2015) 645e650. [11] W.R. Wang, H.P. Gao, Y.L. Mao, J. Alloy Compd. 648 (2015) 75e78. [12] A. Tarafder, A.R. Molla, S. Mukhopadhyay, B. Karmakar, Opt. Mater. 36 (9) (2014) 1463e1470. [13] Y. Ledemi, M.E. Amraoui, J.L. Ferrari, P.L. Fortin, S.J. Ribeiro, Y. Messaddeq, J. Am. Ceram. Soc. 96 (3) (2012) 825e832. [14] D. Chen, Y. Wang, M. Hong, Nano Energy 1 (2012) 73e90. [15] S.F. Zou, Z.L. Zhang, F. Zhang, Y.L. Mao, J. Alloy Compd. 572 (2013) 110e112. [16] Q.J. Chen, W.J. Zhang, X.Y. Huang, G.P. Dong, M.Y. Peng, Q.Y. Zhang, J. Alloy Compd. 513 (2012) 139e144. [17] S. Jiang, H. Guo, X.T. Wei, C.K. Duan, M. Yin, J. Lumin. 152 (2014) 195e198. [18] Y.S. Xu, X.H. Zhang, S.X. Dai, B. Fan, H.L. Ma, J.L. Adam, J. Ren, G.R. Chen, J. Phys. Chem. C 115 (2011) 13056. [19] S.H. Yang, Y.J. Lial, N.J. Cheng, Y.H. Ling, J. Alloys Comp. 489 (2010) 689e693. [20] Y.F. Liu, X. Zhang, Z.D. Hao, Y.S. Luo, X.J. Wang, L. Ma, J.H. Zhang, J. Lumin. 133 (2013) 21e24. [21] C.H. Hsu, S. Das, C.H. Lu, J. Electrochem. Soc. 159 (2012) J193eJ199. [22] W. Lü, Y.S. Luo, Z.D. Hao, X. Zhang, X.J. Wang, J.H. Zhang, Mater. Lett. 77 (2012) 45e47. [23] R.G. Ye, H.P. Ma, C. Zhang, Y.Q. Gao, Youjie Hua, Degang Deng, Ping Liu, Shiqing Xu, J. Alloy Compd. 566 (2013) 73e77. [24] R. Martín-Rodríguez, R. Valiente, M. Bettinelli, Appl. Phys. Lett. 95 (2009) 091913. [25] R. Martín-Rodríguez, R. Valiente, F. Rodríguez, F. Piccinelli, A. Speghini, M. Bettinelli, Phys. Rev. B 82 (2010) 075117. [26] S. Ye, Y.J. Li, D.C. Yu, G.P. Dong, Q.Y. Zhang, J. Mater. Chem. 21 (2011) 3735. [27] E.H. Song, S. Ding, M. Wu, S. Ye, F. Xiao, G.P. Dong, Q.Y. Zhang, J. Mater. Chem. C 1 (2013) 4209. [28] F. Xiao, E.H. Song, S. Ye, Q.Y. Zhang, J. Alloy Compd. 587 (2014) 177e182. [29] S. Heer, M. Wermuth, K. Kr€ amer, H.U. Güdel, Phys. Rev. B 65 (2002) 125112. [30] A.P. Vink, M.A. de Bruin, S. Roke, P.S. Peijzel, A. Meijerink, J. Electrochem. Soc. 148 (7) (2001) E313eE320.
Contents lists available at ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Broadband emission from Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses for glass greenhouse Weirong Wang a, b, Zhangyu Huang a, b, Huiping Gao a, b, Xiuying Cheng a, **, Yanli Mao a, b, * a b
School of Physics and Electronics, Henan University, Kaifeng 475004, China Institute for Computational Materials Science, Henan University, Kaifeng 475004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 February 2016 Received in revised form 16 October 2016 Accepted 19 October 2016
In this work, a kind of oxyfluoride glasses tri-doped with Ce3þ/Mn2þ/Yb3þ ions was prepared by a simple and fast high temperature melting method. Under excitation with 300 nm light, two meaningful broad band emissions (ranged from 340 to 500 nm and 510e700 nm) were obtained, which matched well with the absorption of the chlorophylls. Under near-infrared (980 nm) excitation, an abnormal up-conversion luminescence was demonstrated in the oxyfluoride glasses by the energy transfer from Yb3þ to Mn2þ. In addition, the up-conversion emission has a red shift along with the increase of the doping concentration of Mn2þ, which would contribute to match the action spectrum of photosynthesis better. Our materials will be favored to extend the utilization of solar energy in glass greenhouse for plant cultivation. © 2016 Elsevier B.V. All rights reserved.
Keywords: Oxyfluoride glasses Ce3þ/Mn2þ/Yb3þ Down-conversion Up-conversion Glass greenhouse
1. Introduction Currently, a fast-growing interest has been witnessed on the approaches to improve the photosynthesis of the green plants [1e5]. As one of significant parameters for plant growth, light is not only the energy source of greenery photosynthesis, but also the power source of sprout, blossom, and fruit as well as other morphogenesis for plants. Therefore, the light quality for plants plays a significant role on the harvest. The main light bands absorbed by chlorophyll of greenery are reddish orange (600e700 nm) and bluish violet (400e480 nm) lights, which is only a small percentage of the whole solar spectrum. Longer wavelengths can hardly been absorbed by chlorophylls and other photosynthetic antenna pigments, while the ultraviolet (UV) in the sunlight are even harmful to the plant. Therefore, it is meaningful to convert the useless sunlight to reddish-orange and bluish violet light for improving the utilization level of solar light in the process of photosynthesis.
* Corresponding author. School of Physics and Electronics, Henan University, Kaifeng 475004, China. ** Corresponding author. School of Physics and Electronics, Henan University, Kaifeng 475004, China. E-mail addresses: [email protected] (X. Cheng), [email protected] (Y. Mao). http://dx.doi.org/10.1016/j.optmat.2016.10.037 0925-3467/© 2016 Elsevier B.V. All rights reserved.
In order to promote the growth and achieve higher yields of the crops, many kinds of methods have been studied and used in the past years. Notably, the use of plastic greenhouses in lowtemperature seasons has attracted considerable attention. However, there are still many shortcomings of plastic greenhouse, such as short service lifetime, toxicity to the environment, and chemical instability [6e9]. To solve these problems, the glass greenhouses which show superior performance to the traditional plastic greenhouses in many respects have attracted widely attention [6e9]. The glass materials have better stability against ultraviolet irradiation, better thermal retardation, and excellent chemical durability which directly determines a long service life. Moreover, lanthanide-doped transparent materials have wonderful luminous traits in the UV, visible (Vis) and near-infrared (NIR) wavelength regions [5e18]. Hence, the predominant properties of rare earth doped transparent glass materials allow them to realize promising applications in greenhouses. Recently, solar spectral conversion phosphor has been embedded within a specific reactor device [5,6]. It is experimentally demonstrated that the tune of useless green photons to red can greatly improve the energy harvesting of chlorophylls. However, the complex assembly process and high cost may hinder the development of the device for its large-scale production and application. The solar spectral conversion glass greenhouse can be a
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suitable substitution, for it can be easily assembled and constructed like traditional glass greenhouses. Beneficially, the glass material exhibits excellent resistance to water and corrosion. It is known that the down-conversion (DC) glass material shows an excellent optical performance which is favorable to convert more violet and green photons to red ones via rare-earth or transition-metal ions co-doped in transparent phosphate glasses [7e9]. Likewise, the light use efficiency of photosynthetic systems would also be greatly improved if photosynthesis could use NIR radiation. Therefore, an ability to simultaneously use UV and NIR radiation would a more potential approach to improve the efficiency of photosynthesis. In the previous works, we have studied the Ce3þ/Er3þ/Yb3þ tridoped oxyfluoride glass ceramics for glass greenhouses [11]. The glasses are highly transparent in the visible light range and own intense absorption in the UV and NIR wavelength region. Especially, the glasses can transfer ultraviolet and part of NIR into reddish orange light. However, the emission region of the red light is not broad enough. In addition, the energy transfer between the Ce3þ to Er3þ ions is not very effective. This will result in a poor utilization rate of the materials to sunlight. Hence, the material which not only shows a wider region of excitation but also exhibits a broad emission of bluish violet and reddish orange light is still very promising. The emission of Mn2þ is based on the 4T1g(4G)/6A1g(6S) transition. By introducing an efficient sensitizer, the emission of Mn2þ can be considerably improved. At present, many Mn2þ/Ce3þ co-doped red luminescence materials have been studied, such as ZnS: Ce3þ, Mn2þ [19], Ca3Sc2Si3O12: Ce3þ, Mn2þ [20], MgY4Si3O13: Ce3þ, Mn2þ [21], and Ca4Si2O7F2: Ce3þ, Mn2þ [22] phosphors or Ce3þ/Mn2þ co-doped glass-ceramics containing b-Zn2SiO4 nanocrystals [23]. Furthermore, in order to obtain the broadband upconversion (UC) luminescence, Mn2þ/Yb3þ co-doped phosphors has also been reported and led to some new and unexpected results in the search for novel UC materials and process [24e27]. In this paper, we report the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses. The 50SiO2-20Al2O3-20CaF2-10NaF glasses were selected as the host materials because of its high transparency, lowmelting temperature, simple manufacturing procedure, and good solubility for Ce3þ/Mn2þ/Yb3þ ions. Among the glasses systems, the oxyfluoride glasses are expected to combine the advantages of high mechanical strength of oxide glasses and low phonon energy of fluoride glasses. This will be favored to the energy transfer between neighbor ions. With the broad band excitation of UVeVis and NIR 980 nm lights, a strong and broadband of reddish orange light has been obtained. Furthermore, the energy transfer mechanisms among Ce3þ/Mn2þ/Yb3þ of up and down conversion have also been revealed by detail analysis of the excitation, up and down conversion emission spectra, and the luminescent decay curves of the samples. 2. Experiment section The oxyfluoride glass samples with the compositions in mol% of 50SiO2-20Al2O3-20CaF2-10NaF (G): xCe3þ, yMn2þ, zYb3þ were prepared by high temperature melting method. The doped CeF3 and YbF3 content were fixed to x ¼ 0.1 mol% and z ¼ 5 mol%, while the MnCO3 content was y ¼ 0.1 mol%, 0.5 mol%, 1 mol%, and 1.5 mol % respectively. According to the doping concentration of Ce3þ, Mn2þ and Yb3þ ions, the samples would be denoted further in the text as G:0.1Ce3þ, G:1Mn2þ, G:0.1Ce1Mn, G:0.1Ce0.1Mn5Yb, G:0.1Ce0.5Mn5Yb, G: 0.1Ce1Mn5Yb and G:0.1Ce1.5Mn5Yb, respectively. For each batch, about 10 g raw materials including SiO2 (AR), Al2O3 (AR), CaF2 (AR), NaF (AR), CeF3 (99.9%), MnCO3 (99.9%), YbF3 (99.9%) were mixed thoroughly and then heated in a covered corundum crucible at 1350 C for 2 h to achieve a homogeneous melt, then the melt was cast into a copper mold to process
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quenching. The resulted glasses were kept at 300 C for 120 min in an annealing furnace to relinquish inner stress. The obtained samples were polished to optical quality. The photoluminescence (PL) and the photoluminescence excitation (PLE) spectra were measured by a Tau-3 fluorescence spectrophotometer (Jobin Yvon-Inc, France). Luminescence decay curves and the UC luminescence spectrums were measured with a FLS980E spectrometer (Edinburgh Instruments Ltd., UK). 3. Results and discussion The excitation and emission spectra of the Ce3þ or Mn2þ singly doped glass are shown in Fig. 1(a) and (b). As shown in Fig. 1(a), the PL spectrum of G:0.1Ce3þ displays a broad band extending from 340 to 500 nm, which can be attributed to the typical transition from 5d level to the ground state of Ce3þ. The excitation spectrum monitored at 362 nm shows a broad absorption band within the 250e350 nm UV range, which is due to 4f-5d transition of the Ce3þ. G:1Mn2þ presents a broad band emission centered at 585 nm under 410 nm excitation in Fig. 1(b), which corresponds to the 4 T1(G)/6A1(S) transition of Mn2þ. The excitation spectrum of G:1Mn2þ sample consists of two bands centered at 355 and 410 nm, which are assigned to the transitions from 6A1(S) to 4T2(D) and 4 T1(G) levels of Mn2þ, respectively. Obviously, there is a significant spectral overlap between the Ce3þ PL and Mn2þ PLE spectra as shown in Fig. 1(c), indicating the possibility of energy transfer from Ce3þ to Mn2þ in our oxyfluoride glasses. Fortunately, the assumption is confirmed by the PLE spectra of G:0.1Ce1Mn monitoring the board emission peaks at 585 nm. As shown in Fig. 1(d), three broad excitation bands of 350e500 nm and 250e350 nm can be observed, which respectively corresponding to the transitions from 6A1(S) to 4 T2(D) and 4T1(G) levels of Mn2þ and the 4f-5d transition of the Ce3þ. And it shows the existence of energy transfer from Ce3þ to Mn2þ. The down-conversion emission spectra (ranged from 360 to 680 nm) of the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses has been measured under excitation of 300 nm with a xenon lamp, and illustrated in Fig. 2. It is clearly noticed that all samples exhibit two broad emission band centered at 360 and 620 nm, corresponding to the emission of Ce3þ and Mn2þ, respectively. As the content of Mn2þ increases from 0.1% to 1.5 mol%, the shape and peak positions of the DC emission spectra show no obvious variation. However, the total DC emission intensity and the luminescence intensity distribution are changed largely. By comparing the intensity of Ce3þ ranged from 360 to 500 nm, a gradually decrease trend is showed along with the increase of the concentration of Mn2þ. In addition, the luminescence intensity of Mn2þ also shows a monotone increase along with the doping concentration of Mn2þ increasing from 0.1 to 1 mol%. Further increasing the Mn2þ ions doping concentration would result in emission intensity decrease due to the concentration quenching effect. Fig. 3 show that the decay curves of Ce3þ emission at 362 nm along with various Mn2þ concentrations doping, which corresponds to Ce3þ:5d-4f transition, upon excitation of Ce3þ at 300 nm. With the increase doping concentration of Mn2þ, the deviation from the exponential rule becomes more obvious. By calculation, the average lifetime of Ce3þ ions are found to be about 30.8, 28.2, 24.8, and 22.6 ns corresponding to the G:0.1Ce0.1Mn5Yb, G:0.1Ce0.5Mn5Yb, G:0.1Ce1Mn5Yb and G:0.1Ce1.5Mn5Yb, respectively. Apparently, the fluorescence lifetime of Ce3þ ions in the glass sample become shorter as the concentration of Mn2þ increasing, which is the clear evidence of energy transfer from Ce3þ to Mn2þ in this tri-doped glass systems. According to this DC energy transfer mechanism, the DC emission intensity of Mn2þ should mainly depend on the conversion
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Fig. 1. The excitation and emission spectra of (a) 0.1 mol% Ce3þ -doped glass; (b) 1 mol% Mn2þ -doped glass; (c) spectral overlap between the excitation spectrum for Ce3þ doped glass and emission spectrum for Mn2þ doped glass; (d) The broad excitation spectra of Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses, monitoring at 585 nm.
Fig. 2. The DC emission spectra of the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses as a function of Mn2þ concentration.
efficiency of Ce3þ (from 300 to 360 nm) and the energy transfer rate from Ce3þ to Mn2þ. In all of our samples, the doping concentration of Ce3þ is a constant value of 0.1 mol%, hence, the conversion efficiencies of Ce3þ of all the samples are the same. The energy transfer rate from Ce3þ to Mn2þ depends on the distance between the two ions. From this point of view, the emission intensity of Mn2þ will increase when reducing the distance by increasing Mn2þ concentration into the sample. However, considering the concentration quenching effect, the emission intensity of Mn2þ will decrease when excessive activator ions are doped in to the sample. Therefore, a variation of total DC emission intensity and the luminescence intensity distribution appears, as shown in Fig. 2. Fig. 4 (a) shows the NIR to Vis up-conversion emission spectra of G:0.1Ce0.1Mn5Yb, G:0.1Ce0.5Mn5Yb, G:0.1Ce1Mn5Yb and G:0.1Ce1.5Mn5Yb samples under excitation at 980 nm. The abnormal visible UC emission of Mn2þ is observed in the Ce3þ/ Mn2þ/Yb3þ tri-doped oxyfluoride glasses systems. Moreover, all UC
Fig. 3. The luminescent decay curves of Ce3þ emission at 361 nm by excitation of at 300 nm with various Mn2þ concentration.
spectra exhibit a broad emission band ranging from 510 to 700 nm with a single peak which corresponding to Mn2þ:4T1/6A1. Meanwhile, a monotonically enhancement trend of the UC luminescence intensity with the increase doping concentration of Mn2þ is evidently showed in Fig. 4(b). This increasing phenomenon could be attributed to the increased number of luminescent active ions (Mn2þ ions). It is also indicated that 1.5 mol% is still an appropriate concentration of Mn2þ ions for emission in UC process although a quenching has happened in the down-conversion process. Furthermore, with the increasing variation of the content of Mn2þ, an obvious red shift of UC luminescence can also be found in Fig. 4(a) from 560 to 620 nm with about 20 nm interval linear growth. This is a good sign, as it can make the UC luminescence spectrum match better with the absorption spectrum of
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Fig. 4. (a) UC emission spectra and (b) Mn2þ emission intensities of the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses as a function of Mn2þ concentration.
chlorophyll. Hence, it can be feasible to use as our photo-converting material for promoting the growth of plants. According to the above results, a most possible UC energy transfer mechanism between Mn2þ/Yb3þ can be proposed, as schematically illustrated in Fig. 5. At first, a small quantity of Mn2þ (0.1 mol%) was doped into the oxyfluoride glass system. On account of the existence of Yb3þ, a dimer of Yb3þ-Mn2þ will form. Under excitation by a 980 nm laser diode, a visible green emission centered at 560 nm can be seen and detected via two kinds of corresponding ground state absorption (GSA) and excited state absorption (ESA) UC mechanism, as shown in Fig. 5. Because Mn2þ ions have no intermediate excitation states resonant with Yb3þ ions, the GSA/ESA cannot occur simultaneously in single Yb3þ or Mn2þ. So both Yb3þ and Mn2þ ions should be involved in the UC mechanism. When two Yb3þ ions combine their excitation energy by a cooperative process to transfer it to the nearby Mn2þ (or Mn2þ pairs) simultaneously, then they will gives the red (or green) emission [27,28]. When adding more Mn2þ into the system, more Yb3þ-Mn2þ dimers (or even Yb3þ-Mn2þ-Mn2þ trimer) will form. The distance between Yb3þand Mn2þ may also reduced, which will
result in an increased energy transfer rate from Yb3þ to Mn2þ. Additionally, as more Mn2þ adding in to the glass system, the size of the Yb3þ-Mn2þ dimer will become larger as well, according to the size effect, a red shift UC luminescence appears. [24,28e30]. It is known that the solar radiation onto the earth's surface has wavelengths ranging from about 200 nm for ultraviolet radiation to about 2500 nm for infrared radiation. However, the radiation in the 200e280 nm wavelength region (also called the solar blind region) of solar spectrum could hardly reach the surface of the earth because nearly all of them are absorbed by ozonosphere existing in the upper atmosphere. The solar radiation spectrum in the 280e1800 nm wavelength region was showed in Fig. 6. The UV wavelength light of 280e400 nm cannot be absorbed by plants and even does harm to plants. Hence, it is significant to realize the conversion of this part of the solar light into useful light for plant. Herein, we prepared tri-doped Ce3þ/Mn2þ/Yb3þ oxyfluoride glasses which showed an outstanding transparency, as shown in the insert picture of Fig. 6. Ce3þ is known as an effective conversion ions to realize the conversion of light from ultraviolet (280e400 nm) to blue-violet (340e500 nm), which precisely match the absorption of
Fig. 5. Schematic representation of the proposed UC mechanism in the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses.
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Acknowledgements This work is supported by Science and Technology Research Project of Henan Province (No. 142102210389), the National Natural Science Foundation of China (Grant No. 21103043), The Program for Science and Technology Innovation Talents in Universities of Henan Province (No.16HASTIT043) and the Program for Innovative Research Team (in Science and Technology) in University of Henan Province (No. 13IRTSTHN017).
References
Fig. 6. Solar radiation spectrum in the 280e1800 nm wavelength region. The inset shows the picture of the samples with 0.1 mol% and 1 mol% of Mn2þ of the Ce3þ/Mn2þ/ Yb3þ tri-doped oxyfluoride glasses.
chlorophyll. Moreover, a confirmed energy transfer process from Ce3þ to Mn2þ can also improve the emission of Mn2þ, due to the high absorption coefficient of Ce3þ. In addition, a broad band emission ranging from 510 to 700 nm of Mn2þ ions also match well of the red region absorption of chlorophyll. Therefore, an effective convertor for photosynthesis luminescence conversion can be obtained via DC energy transfer process. Additionally, a rare UC energy transfer process from Yb3þ to Mn2þ has also been found, which is an another route to get a broad reddish orange light. This will improve the utilization of the NIR light of sunlight for green plant photosynthesis. Thus, it is indicated that the material will have a great application prospect in use of greenhouse. 4. Conclusions In summary, the Ce3þ/Mn2þ/Yb3þ tri-doped oxyfluoride glasses have been synthesized. In our glasses system, Ce3þ exhibits an intense UV-blue emission in the range of 340e500 nm. Meanwhile, Mn2þ shows an intense red emission band peaked at 585 nm due to the effective energy transfer from Ce3þ to Mn2þ ions. Furthermore, an efficient broadband UC luminescence upon 980 nm laser excitation was also investigated systematically. These glasses have broad band excitation, and can simultaneously convert the UVeVis and NIR lights into bluish violet and red lights, which is beneficial to the photosynthesis of the green plants. The down-converting and up-converting materials can enrich the action spectrum of photosynthesis in the UV, Vis and NIR range. Thus, our oxyfluoride glasses can be applied to the glass greenhouse for improving the photosynthesis of the green plants.
[1] X.G. Zhu, S.P. Long, D.R. Ort, Annu. Rev. Plant Biol. 61 (2010) 235e261. [2] A. Graf, A.M. Smith, Trends Plant Sci. 16 (3) (2011) 169e175. [3] R.E. Nlankenship, D.M. Tiede, J. Barber, G.W. Brudvig, G. Fleming, M. Ghirardi, Science 332 (2011) 805. €rvi, J. Ho € lsa €, E. Tyystj€ [4] T. Antal, E. Harju, L. Pihlgren, M. Lastusaari, T. Tyystja arvi, Int. J. Hydrogen Energy 37 (2012) 8859e8863. [5] L. Wondraczek, M. Batenschuk, M.A. Schmidt, R. Borchardt, S. Scheiner, B. Seemann, P. Scheizer, C.J. Brabec, Nat. Commun. 4 (2013). No. Art. no. 2047. [6] Q. Xia, M. Batentschuk, A. Osvet, P. Richter, D.-P. H€ ader, J. Schneider, C.J. Brabec, L. Wondraczek, A. Winnacker, Opt. Exp. 21 (2013) A909. [7] C.G. Ming, F. Song, L.Q. An, X.B. Ren, Appl. Phys. Lett. 102 (2013) 14903. [8] C.G. Ming, F. Song, X.B. Ren, L.Q. An, Appl. Phys. Lett. 103 (2013) 041906. [9] Y.D. Han, F. Song, Q. Li, F.X. Wang, C.G. Ming, J.G. Tian, Opt. Mater. 37 (2014) 756e759. [10] T.H. Lv, X.H. Xu, X. Yu, D. Zhou, J. Qiu, Ceram. Int. 41 (2015) 645e650. [11] W.R. Wang, H.P. Gao, Y.L. Mao, J. Alloy Compd. 648 (2015) 75e78. [12] A. Tarafder, A.R. Molla, S. Mukhopadhyay, B. Karmakar, Opt. Mater. 36 (9) (2014) 1463e1470. [13] Y. Ledemi, M.E. Amraoui, J.L. Ferrari, P.L. Fortin, S.J. Ribeiro, Y. Messaddeq, J. Am. Ceram. Soc. 96 (3) (2012) 825e832. [14] D. Chen, Y. Wang, M. Hong, Nano Energy 1 (2012) 73e90. [15] S.F. Zou, Z.L. Zhang, F. Zhang, Y.L. Mao, J. Alloy Compd. 572 (2013) 110e112. [16] Q.J. Chen, W.J. Zhang, X.Y. Huang, G.P. Dong, M.Y. Peng, Q.Y. Zhang, J. Alloy Compd. 513 (2012) 139e144. [17] S. Jiang, H. Guo, X.T. Wei, C.K. Duan, M. Yin, J. Lumin. 152 (2014) 195e198. [18] Y.S. Xu, X.H. Zhang, S.X. Dai, B. Fan, H.L. Ma, J.L. Adam, J. Ren, G.R. Chen, J. Phys. Chem. C 115 (2011) 13056. [19] S.H. Yang, Y.J. Lial, N.J. Cheng, Y.H. Ling, J. Alloys Comp. 489 (2010) 689e693. [20] Y.F. Liu, X. Zhang, Z.D. Hao, Y.S. Luo, X.J. Wang, L. Ma, J.H. Zhang, J. Lumin. 133 (2013) 21e24. [21] C.H. Hsu, S. Das, C.H. Lu, J. Electrochem. Soc. 159 (2012) J193eJ199. [22] W. Lü, Y.S. Luo, Z.D. Hao, X. Zhang, X.J. Wang, J.H. Zhang, Mater. Lett. 77 (2012) 45e47. [23] R.G. Ye, H.P. Ma, C. Zhang, Y.Q. Gao, Youjie Hua, Degang Deng, Ping Liu, Shiqing Xu, J. Alloy Compd. 566 (2013) 73e77. [24] R. Martín-Rodríguez, R. Valiente, M. Bettinelli, Appl. Phys. Lett. 95 (2009) 091913. [25] R. Martín-Rodríguez, R. Valiente, F. Rodríguez, F. Piccinelli, A. Speghini, M. Bettinelli, Phys. Rev. B 82 (2010) 075117. [26] S. Ye, Y.J. Li, D.C. Yu, G.P. Dong, Q.Y. Zhang, J. Mater. Chem. 21 (2011) 3735. [27] E.H. Song, S. Ding, M. Wu, S. Ye, F. Xiao, G.P. Dong, Q.Y. Zhang, J. Mater. Chem. C 1 (2013) 4209. [28] F. Xiao, E.H. Song, S. Ye, Q.Y. Zhang, J. Alloy Compd. 587 (2014) 177e182. [29] S. Heer, M. Wermuth, K. Kr€ amer, H.U. Güdel, Phys. Rev. B 65 (2002) 125112. [30] A.P. Vink, M.A. de Bruin, S. Roke, P.S. Peijzel, A. Meijerink, J. Electrochem. Soc. 148 (7) (2001) E313eE320.