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Multicolor-tunable upconversion emission of lanthanide doped 12CaO·7Al2O3 polycrystals
Materials Letters 220 (2018) 269–271
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Multicolor-tunable upconversion emission of lanthanide doped 12CaO7Al2O3 polycrystals Yannan Qian a,⇑, Xunze Tang a, ZhengYu Zhang a, Haiyan Zhang a,⇑, Maxim Ivanov b,c, Qibai Wu a a
School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China Institute of Electrophysics of the Ural Branch of Russian Academy of Sciences, Ekaterinburg 620016, Russia c Ural Federal University, Ekaterinburg 620002, Russia b
a r t i c l e
i n f o
Article history: Received 5 December 2017 Received in revised form 20 February 2018 Accepted 24 February 2018 Available online 27 February 2018 Keywords: 12CaO7Al2O3 Color tunable upconversion emission Luminescence Optical materials and properties
a b s t r a c t A novel multicolor-tunable lanthanide doped 12CaO7Al2O3 (Ln3+:C12A7; Ln3+ = Yb3+, Tm3+ and Er3+) synthesized by solid-state reaction method would greatly enhance the scope of its applications ranging from infrared solar cells to field emission display. The scanning electron microscopy (SEM) was used to characterize the morphology of Ln3+:C12A7. Under 980 nm excitation, the emission color was tuned from green-yellow to red region through adjusting the concentrations of Ln3+ ions. The obtained near infrared upconversion (UC) emissions in Ln3+:C12A7 was corresponded to ‘‘window of optical transparency”. All blue, green and red UC emissions were populated by one-photon process, and the proposed UC mechanisms were studied in Ln3+:C12A7. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Lanthanide doped 12CaO7Al2O3 (Ln3+:C12A7) has been gained much attention because it has the ability of tuning UC color to meet the need of a specific application, such as a specified color to pinpoint the organelles in a single cell and to detect disease markers in a blood drop [1]. The unique caged structure 12CaO7Al2O3, expressed as [Ca24Al28O64]4+2(O2) [2], has potential applications in ion conducting solid electrolyte, solar cells and transparent transistors [3]. Especially, C12A7 could be as a promising UC luminescent host material due to the precise control of electronic structure [4]. C12A7 belongs to a cubic space group
I 4 3d with a lattice constant of 11.99 Å [5]. There are two conduction bands (CB) in the electron doped C12A7 [6]. The upper CB named as framework conduction band (FCB) is caused by the cation sites of the framework. The narrow cage conduction band (CCB) in the lower is formed by the states associated with cages. When the trapped electrons occupy CCB, the ground states of encaged ions are close to the top of valence band, leading to the associated electronic state perturbation and the effect of electron-hole processes in C12A7. To obtain the multicolor applications, Ln3+ ions doped fluorides and oxides have been studied extensively. Prof. S.C. Gan tuned the
⇑ Corresponding authors. E-mail address: [email protected] (Y. Qian). https://doi.org/10.1016/j.matlet.2018.02.116 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
color tones from green, through yellow, to red by adjusting the concentration of Eu3+ ions in Eu3+/Tb3+:GdOF crystals [7]. It has been reported by L. Liu that the multicolor-emitting luminescence were obtained in Eu3+, Tb3+, Dy3+, Sm3+/Ce3+:NaGdF4 core/shell materials synthesized by hydrothermal in situ ion-exchange approach [8]. R. Wang et al. pay attention to obtain white UC emission in Tm3+:Yb3+:Er3+:C12A7 polycrystal and Tm3+:Yb3+:Ho3+: C12A7 single crystal under 980 nm excitation [9,10]. However, the multicolor-tunable UC emission and NIR emissions are not discussed in their works. On the other hand, the near-infrared (NIR) emission arising from the transition 3H4 ? 3H6 of Tm3+ ion within the spectral range of 750 nm–1000 nm could be considered a ‘‘window of optical transparency” for biological tissues [11]. Paras N. Prasad used successfully the core/shell (NaYbF4:Gd3+ 30%/Tm3+ 0.5%)/NaYF4 nanoparticles as the imaging contrast agents in a nude mouse [12]. Therefore, it is essential to study scientifically the role of Ln3+ for multicolor-tunable emissions in Ln3+:C12A7. 2. Experimental Ln3+:C12A7 polycrystals were synthesized by solid-state reaction method. The CaCO3, Al2O3 and Ln2O3 (99.99% purity, Aladdin. Co.) with the stoichiometric ratio Ca:Al of 12:14 were ball-milled at a speed of 180 rpm for 12 h. Then the mixtures were heated at 800 °C and 1350 °C for 4 h and 10 h, respectively. Ln3+:C12A7 codoped with (1#) 1.0 mol% Yb3+, 0.5 mol% Tm3+ and 3.0 mol% Er3+, (2#) 3.0 mol% Yb3+, 0.5 mol% Tm3+ and 1.0 mol% Er3+, (3#)
270
Y. Qian et al. / Materials Letters 220 (2018) 269–271
3.0 mol% Yb3+, 0.5 mol% Tm3+ and 0.5 mol% Er3+ and (4#) 3.0 mol% Yb3+, 1.0 mol% Tm3+ and 0.5 mol% Er3+, respectively. The size and morphology were examined by using SEM (SU8010, Hitachi, Ltd. Japan). The UC emission spectra were excited by a power-controllable 980 nm diode laser and recorded by the spectrometer (MDL-III-980/ZolixScanBasic, Zolix Instruments Co. LTD, Beijing). The CIE chromaticity coordinates for UC emissions ranged from 400 nm to 750 mm were calculated based on 1931 CIE standard and marked in the CIE standard chromaticity diagram. 3. Results and discussion Fig. 1 shows the crystal phase and morphology of Yb3+/Tm3+/ Er3+:C12A7 polycrystals. SEM images in Fig. 1(a)–(d) display that the slightly aggregated particles have an approximately spherical shape, and the narrow size range is about 150 nm –250 nm in Yb3+/Tm3+/Er3+:C12A7. XRD patterns presented in Fig. 1(e) illustrate that all of the strong and sharp diffraction peaks are consistent with the standard card of C12A7 (JCPDS: 09-0413). No new peaks appear in Yb3+/Tm3+/Er3+:C12A7, indicating the phase purity of C12A7 product. Fig. 2 shows UC emission spectra of Ln3+:C12A7 under 980 nm excitation. The blue, green, red and NIR UC emissions centered at 476 nm, 524/550 nm, 665 nm and 791 nm are easily assigned to the transitions of Tm3+:1G4 ? 3H6, Er3+:2H11/2/4S3/2 ? 4I15/2, Er3+:4F9/2 ? 4I15/2 and Tm3+:3H4 ? 3H6, respectively [13]. The strongest intensities of blue, green and NIR UC emissions are observed in sample 4#, while the red UC one is weakest. Comparison of sample 3# with 4# indicates the red UC emission decreases with increasing Tm3+ content when Yb3+ and Er3+ contents are constant. And for Tm3+ of 0.5 mol% and Yb3+ of 3.0 mol%, the intensity
Fig. 2. The UC emission spectra of Ln3+:C12A7 under 980 nm excitation. The inset is the calculated color coordinates for Ln3+:C12A7 polycrystals.
of NIR UC emission reduces with the enhanced Er3+ concentration. The intense NIR UC emission indicates that Yb3+/Tm3+/Er3+:C12A7 will be suitable for potential bio-imaging. To reflect the true color of luminescence, the CIE 1931 color coordinates (x, y) are calculated to be (0.33, 0.56), (0.55, 0.40), (0.65, 0.34) and (0.67, 0.31), respectively, for 4#, 3#, 1#, and 2#. Obviously, the color tone changes from green-yellow (0.33, 0.56) to red (0.67, 0.31) region of 1931 CIE diagram, suggesting that Ln3+:C12A7 have the potential applications in multicolor displays. The role of Ln3+ for multicolor-tunable emissions in Ln3+:C12A7 can be understood by energy transfer between Er3+ and Tm3+ ions. As shown in Fig. 3, the green emitting 4F7/2 state of Er3+ is populated from Yb3+ ion by ET1 and ET2 Yb3þ ða 980nm photonÞ
Yb3þ ða 980nm photonÞ
4 ! I11=2 ðErÞ ! F 7=2 ðErÞ). Alter(4 I15=2 ðErÞ natively, Er3+ ions at the 4I11/2 state could relax nonradiatively to 4 I13/2 state, and further populate the red 4F9/2 state by ET3 of 4 I13/2 Er + 2F5/2 Yb ? 4F9/2 Er + 2F7/2 Yb. As for Tm3+ ion, the 1G4 state is populated successively by ET4, ET5 and ET6 processes:
3
H6 ðTmÞ
Yb3þ ða 980nm photonÞ 3
!
Yb
3þ
ða 980nm photonÞ 3
Yb
3þ
ða 980nm photonÞ 1
!
!
H5 ðTmÞ
F 2;3 ðTmÞ
nonradiative relaxation 3
!
nonradiative relaxation 3
!
F 4 ðTmÞ
H4 ðTmÞ
G4 ðTmÞ
Fig. 2[14]
4
1
G4
3
F2,3
F7/2
2
4
H11/2
2.0x10
4
ET6
F9/2
F5/2
4
I11/2
CR
ET5
2 4
1.0x10
3
ET3
4
1.5x10
ET2
-1
Energy (cm )
S3/2
4
2 3
4
I13/2
3
3
2 0.0
F7/2
ET4
ET1
5.0x10
I15/2
Yb
Er
3+
Tm
3+
F5/2
H5
F4
3
4
3+
Fig. 1. crystal phase and morphology of Ln3+:C12A7 polycrystals, (a)–(d) SEM images of 1#, 2#, 3# and 4#, respectively, and (e) XRD patterns.
H4
2
H6
F7/2
3+
Yb
Fig. 3. Energy level diagram of Ln3+ ions under laser excitation of 980 nm.
Y. Qian et al. / Materials Letters 220 (2018) 269–271
4. Conclusions
1# = 0.88 2# = 0.84 3# = 1.09 4# = 0.75
2.6
Red emission
2.8
3.0
3.2
Log (Intensity (a.u.))
1# = 0.82
The morphology of Yb3+/Tm3+/Er3+:C12A7 presents slightly aggregated spherical shape of 150 nm–250 nm. The emission color tuned from red-yellow (0.55, 0.40) to green-yellow (0.33, 0.56) is attributed to the efficient CR process of 4I13/2 Er + 3H4 Tm ? 4S3/2 Er + 3H6 Tm between Er3+ and Tm3+ ions. Under 980 nm excitation, one-photon process to populate the blue, green and red UC emissions is found in Yb3+/Tm3+/Er3+:C12A7. The bright NIR UC emission at 791 nm is also observed, which is also favorable to use as a ‘‘window of optical transparency” for biological tissues. Acknowledgements
2# = 0.87 3# = 0.89 4# = 0.62
Green emission
2.4
2.7
1# = 1.00 2# = 1.11 3# = 1.18 4# = 0.78
2.4
271
3.0
Blue emission
2.7
3.0
Log (Pump power (mW)) Fig. 4. Pump power dependence in a logarithmic diagram under 980 nm excitation.
For an ‘‘unsaturated’’ UC process, the intensity of UC emission (If) depends on the excitation power (P) according to the power law If / Pn [15], where n is the absorbed photon numbers to populate the UC emission. As illustrated in Fig. 4, the slopes of 1#, 2#, 3# and 4# are to be 0.88, 0.84, 1.09 and 0.75 for red UC emission, 0.82, 0.87, 0.89 and 0.62 for green UC emission, 1.00, 1.11, 1.18 and 0.78 for blue UC emission, respectively. This is an indication that one-photon process is responsible for populating all blue, green and red UC emissions in Yb3+/Tm3+/Er3+:C12A7, which has been also found in Ho3+/Yb3+/Tm3+:LiNbO3 polycrystals under 980 nm excitation [16]. Here, one-photon process could be attributed to the competition between the linear decay and UC process for the depletion of the intermediate excited states [17].
This work was supported by the Guangdong Natural Science Funds for Distinguished young scholar (No.:2015A030306041), the tiptop Scientific and Technical Innovative Youth Talents of Guangdong special support program (No.:2015TQ01N060), the National Natural Science Foundation of China (No.:11304402), the link project of the National Natural Science Foundation of China and Guangdong Province (No.: U1401246), Act 211 Government of the RF (№ 02.A03.21.0006), NSFC-RFBR (Grant No. 1151101157/1 6-52-53059-UUEH_a) and Program of Presidium of RAS (No. 1517-2-20). References [1] F.Y. Xie, J.H. Li, Z.Y. Dong, D.W. Wen, J.X. Shi, J. Yan, M.M. Wu, RSC Adv. 5 (2015) 59830. [2] N. Kuganathan, H. Hosono, A.L. Shluger, P.V. Sushko, J. Am. Chem. Soc. 136 (2014) 2216–2219. [3] X.L. Liu, Y.X. Liu, D.T. Yan, H.C. Zhu, C.G. Liu, C.S. Xu, Y.C. Liu, X.J. Wang, J. Mater. Chem. 22 (2012) 16839–16843. [4] Y.Q. Mao, Y.P. Pu, J.F. Wei, Mater. Res. Inn. 15 (2011) 260–263. [5] Y.R. Yin, Z.T. Jia, W.X. Mu, Z.L. Gao, J. Zhang, X.T. Tao, Cryst. Growth Des. 16 (2016) 1903–1906. [6] P.V. Sushko, A.L. Shluger, K. Hayashi, M. Hirano, H. Hosono, Phys. Rev. Lett. 91 (2003) 126401–126404. [7] R.Q. Li, H.L. Xiong, Y.M. Liang, Y.L. Liu, N.N. Zhang, S.C. Gan, New J. Chem. 40 (2016) 1792–1798. [8] L. Liu, N.N. Zhang, Z.H. Leng, Y.M. Liang, R.Q. Li, L.C. Zou, S.C. Gan, Dalton Trans. 44 (2015) 6645–6654. [9] Y.F. Qu, R. Wang, Z.Z. Qiu, Y. Tao, J.J. Zhou, Opt. Mater. Express 5 (2015) 1881– 1889. [10] J.C. Sun, R. Wang, L.F. Wu, Z.Z. Qiu, L.L. Xing, Y.F. Qu, X.J. Ai, Sci. Adv. Mater. 4 (2012) 669–672. [11] D.Q. Chen, Y.L. Yu, F. Huang, H. Lin, P. Huang, A.P. Yang, Z.X. Wang, Y.S. Wang, J. Mater. Chem. 22 (2012) 2632–2640. [12] J.A. Damasco, G.Y. Chen, W. Shao, H. Ågren, H.Y. Huang, W.T. Song, J.F. Lovell, P. N. Prasad, ACS Appl. Mater. Interfaces 6 (2014) 13884–13893. [13] M.Y. Ding, D.Q. Chen, Z.Y. Wan, Y. Zhou, J.S. Zhong, J.H. Xi, Z.G. Ji, J. Mater. Sci. 50 (2015) 6779–6785. [14] K.Z. Zheng, Y. Liu, Z.Y. Liu, Z. Chen, W.P. Qin, Dalton Trans. 42 (2013) 5159– 5166. [15] J.S. Liao, L.L. Nie, S.H. Liu, B. Liu, H.R. Wen, J. Mater. Sci. 49 (2014) 6081–6086. [16] L.L. Xing, R. Wang, W. Xu, Y.N. Qian, Y.L. Xu, C.H. Yang, X.R. Liu, J. Lumin. 132 (2012) 1568–1574. [17] Y.N. Qian, B. Wang, R. Wang, L.L. Xing, Y.L. Xu, RSC Adv. 3 (2013) 13507–13514.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Multicolor-tunable upconversion emission of lanthanide doped 12CaO7Al2O3 polycrystals Yannan Qian a,⇑, Xunze Tang a, ZhengYu Zhang a, Haiyan Zhang a,⇑, Maxim Ivanov b,c, Qibai Wu a a
School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China Institute of Electrophysics of the Ural Branch of Russian Academy of Sciences, Ekaterinburg 620016, Russia c Ural Federal University, Ekaterinburg 620002, Russia b
a r t i c l e
i n f o
Article history: Received 5 December 2017 Received in revised form 20 February 2018 Accepted 24 February 2018 Available online 27 February 2018 Keywords: 12CaO7Al2O3 Color tunable upconversion emission Luminescence Optical materials and properties
a b s t r a c t A novel multicolor-tunable lanthanide doped 12CaO7Al2O3 (Ln3+:C12A7; Ln3+ = Yb3+, Tm3+ and Er3+) synthesized by solid-state reaction method would greatly enhance the scope of its applications ranging from infrared solar cells to field emission display. The scanning electron microscopy (SEM) was used to characterize the morphology of Ln3+:C12A7. Under 980 nm excitation, the emission color was tuned from green-yellow to red region through adjusting the concentrations of Ln3+ ions. The obtained near infrared upconversion (UC) emissions in Ln3+:C12A7 was corresponded to ‘‘window of optical transparency”. All blue, green and red UC emissions were populated by one-photon process, and the proposed UC mechanisms were studied in Ln3+:C12A7. Ó 2018 Elsevier B.V. All rights reserved.
1. Introduction Lanthanide doped 12CaO7Al2O3 (Ln3+:C12A7) has been gained much attention because it has the ability of tuning UC color to meet the need of a specific application, such as a specified color to pinpoint the organelles in a single cell and to detect disease markers in a blood drop [1]. The unique caged structure 12CaO7Al2O3, expressed as [Ca24Al28O64]4+2(O2) [2], has potential applications in ion conducting solid electrolyte, solar cells and transparent transistors [3]. Especially, C12A7 could be as a promising UC luminescent host material due to the precise control of electronic structure [4]. C12A7 belongs to a cubic space group
I 4 3d with a lattice constant of 11.99 Å [5]. There are two conduction bands (CB) in the electron doped C12A7 [6]. The upper CB named as framework conduction band (FCB) is caused by the cation sites of the framework. The narrow cage conduction band (CCB) in the lower is formed by the states associated with cages. When the trapped electrons occupy CCB, the ground states of encaged ions are close to the top of valence band, leading to the associated electronic state perturbation and the effect of electron-hole processes in C12A7. To obtain the multicolor applications, Ln3+ ions doped fluorides and oxides have been studied extensively. Prof. S.C. Gan tuned the
⇑ Corresponding authors. E-mail address: [email protected] (Y. Qian). https://doi.org/10.1016/j.matlet.2018.02.116 0167-577X/Ó 2018 Elsevier B.V. All rights reserved.
color tones from green, through yellow, to red by adjusting the concentration of Eu3+ ions in Eu3+/Tb3+:GdOF crystals [7]. It has been reported by L. Liu that the multicolor-emitting luminescence were obtained in Eu3+, Tb3+, Dy3+, Sm3+/Ce3+:NaGdF4 core/shell materials synthesized by hydrothermal in situ ion-exchange approach [8]. R. Wang et al. pay attention to obtain white UC emission in Tm3+:Yb3+:Er3+:C12A7 polycrystal and Tm3+:Yb3+:Ho3+: C12A7 single crystal under 980 nm excitation [9,10]. However, the multicolor-tunable UC emission and NIR emissions are not discussed in their works. On the other hand, the near-infrared (NIR) emission arising from the transition 3H4 ? 3H6 of Tm3+ ion within the spectral range of 750 nm–1000 nm could be considered a ‘‘window of optical transparency” for biological tissues [11]. Paras N. Prasad used successfully the core/shell (NaYbF4:Gd3+ 30%/Tm3+ 0.5%)/NaYF4 nanoparticles as the imaging contrast agents in a nude mouse [12]. Therefore, it is essential to study scientifically the role of Ln3+ for multicolor-tunable emissions in Ln3+:C12A7. 2. Experimental Ln3+:C12A7 polycrystals were synthesized by solid-state reaction method. The CaCO3, Al2O3 and Ln2O3 (99.99% purity, Aladdin. Co.) with the stoichiometric ratio Ca:Al of 12:14 were ball-milled at a speed of 180 rpm for 12 h. Then the mixtures were heated at 800 °C and 1350 °C for 4 h and 10 h, respectively. Ln3+:C12A7 codoped with (1#) 1.0 mol% Yb3+, 0.5 mol% Tm3+ and 3.0 mol% Er3+, (2#) 3.0 mol% Yb3+, 0.5 mol% Tm3+ and 1.0 mol% Er3+, (3#)
270
Y. Qian et al. / Materials Letters 220 (2018) 269–271
3.0 mol% Yb3+, 0.5 mol% Tm3+ and 0.5 mol% Er3+ and (4#) 3.0 mol% Yb3+, 1.0 mol% Tm3+ and 0.5 mol% Er3+, respectively. The size and morphology were examined by using SEM (SU8010, Hitachi, Ltd. Japan). The UC emission spectra were excited by a power-controllable 980 nm diode laser and recorded by the spectrometer (MDL-III-980/ZolixScanBasic, Zolix Instruments Co. LTD, Beijing). The CIE chromaticity coordinates for UC emissions ranged from 400 nm to 750 mm were calculated based on 1931 CIE standard and marked in the CIE standard chromaticity diagram. 3. Results and discussion Fig. 1 shows the crystal phase and morphology of Yb3+/Tm3+/ Er3+:C12A7 polycrystals. SEM images in Fig. 1(a)–(d) display that the slightly aggregated particles have an approximately spherical shape, and the narrow size range is about 150 nm –250 nm in Yb3+/Tm3+/Er3+:C12A7. XRD patterns presented in Fig. 1(e) illustrate that all of the strong and sharp diffraction peaks are consistent with the standard card of C12A7 (JCPDS: 09-0413). No new peaks appear in Yb3+/Tm3+/Er3+:C12A7, indicating the phase purity of C12A7 product. Fig. 2 shows UC emission spectra of Ln3+:C12A7 under 980 nm excitation. The blue, green, red and NIR UC emissions centered at 476 nm, 524/550 nm, 665 nm and 791 nm are easily assigned to the transitions of Tm3+:1G4 ? 3H6, Er3+:2H11/2/4S3/2 ? 4I15/2, Er3+:4F9/2 ? 4I15/2 and Tm3+:3H4 ? 3H6, respectively [13]. The strongest intensities of blue, green and NIR UC emissions are observed in sample 4#, while the red UC one is weakest. Comparison of sample 3# with 4# indicates the red UC emission decreases with increasing Tm3+ content when Yb3+ and Er3+ contents are constant. And for Tm3+ of 0.5 mol% and Yb3+ of 3.0 mol%, the intensity
Fig. 2. The UC emission spectra of Ln3+:C12A7 under 980 nm excitation. The inset is the calculated color coordinates for Ln3+:C12A7 polycrystals.
of NIR UC emission reduces with the enhanced Er3+ concentration. The intense NIR UC emission indicates that Yb3+/Tm3+/Er3+:C12A7 will be suitable for potential bio-imaging. To reflect the true color of luminescence, the CIE 1931 color coordinates (x, y) are calculated to be (0.33, 0.56), (0.55, 0.40), (0.65, 0.34) and (0.67, 0.31), respectively, for 4#, 3#, 1#, and 2#. Obviously, the color tone changes from green-yellow (0.33, 0.56) to red (0.67, 0.31) region of 1931 CIE diagram, suggesting that Ln3+:C12A7 have the potential applications in multicolor displays. The role of Ln3+ for multicolor-tunable emissions in Ln3+:C12A7 can be understood by energy transfer between Er3+ and Tm3+ ions. As shown in Fig. 3, the green emitting 4F7/2 state of Er3+ is populated from Yb3+ ion by ET1 and ET2 Yb3þ ða 980nm photonÞ
Yb3þ ða 980nm photonÞ
4 ! I11=2 ðErÞ ! F 7=2 ðErÞ). Alter(4 I15=2 ðErÞ natively, Er3+ ions at the 4I11/2 state could relax nonradiatively to 4 I13/2 state, and further populate the red 4F9/2 state by ET3 of 4 I13/2 Er + 2F5/2 Yb ? 4F9/2 Er + 2F7/2 Yb. As for Tm3+ ion, the 1G4 state is populated successively by ET4, ET5 and ET6 processes:
3
H6 ðTmÞ
Yb3þ ða 980nm photonÞ 3
!
Yb
3þ
ða 980nm photonÞ 3
Yb
3þ
ða 980nm photonÞ 1
!
!
H5 ðTmÞ
F 2;3 ðTmÞ
nonradiative relaxation 3
!
nonradiative relaxation 3
!
F 4 ðTmÞ
H4 ðTmÞ
G4 ðTmÞ
Fig. 2[14]
4
1
G4
3
F2,3
F7/2
2
4
H11/2
2.0x10
4
ET6
F9/2
F5/2
4
I11/2
CR
ET5
2 4
1.0x10
3
ET3
4
1.5x10
ET2
-1
Energy (cm )
S3/2
4
2 3
4
I13/2
3
3
2 0.0
F7/2
ET4
ET1
5.0x10
I15/2
Yb
Er
3+
Tm
3+
F5/2
H5
F4
3
4
3+
Fig. 1. crystal phase and morphology of Ln3+:C12A7 polycrystals, (a)–(d) SEM images of 1#, 2#, 3# and 4#, respectively, and (e) XRD patterns.
H4
2
H6
F7/2
3+
Yb
Fig. 3. Energy level diagram of Ln3+ ions under laser excitation of 980 nm.
Y. Qian et al. / Materials Letters 220 (2018) 269–271
4. Conclusions
1# = 0.88 2# = 0.84 3# = 1.09 4# = 0.75
2.6
Red emission
2.8
3.0
3.2
Log (Intensity (a.u.))
1# = 0.82
The morphology of Yb3+/Tm3+/Er3+:C12A7 presents slightly aggregated spherical shape of 150 nm–250 nm. The emission color tuned from red-yellow (0.55, 0.40) to green-yellow (0.33, 0.56) is attributed to the efficient CR process of 4I13/2 Er + 3H4 Tm ? 4S3/2 Er + 3H6 Tm between Er3+ and Tm3+ ions. Under 980 nm excitation, one-photon process to populate the blue, green and red UC emissions is found in Yb3+/Tm3+/Er3+:C12A7. The bright NIR UC emission at 791 nm is also observed, which is also favorable to use as a ‘‘window of optical transparency” for biological tissues. Acknowledgements
2# = 0.87 3# = 0.89 4# = 0.62
Green emission
2.4
2.7
1# = 1.00 2# = 1.11 3# = 1.18 4# = 0.78
2.4
271
3.0
Blue emission
2.7
3.0
Log (Pump power (mW)) Fig. 4. Pump power dependence in a logarithmic diagram under 980 nm excitation.
For an ‘‘unsaturated’’ UC process, the intensity of UC emission (If) depends on the excitation power (P) according to the power law If / Pn [15], where n is the absorbed photon numbers to populate the UC emission. As illustrated in Fig. 4, the slopes of 1#, 2#, 3# and 4# are to be 0.88, 0.84, 1.09 and 0.75 for red UC emission, 0.82, 0.87, 0.89 and 0.62 for green UC emission, 1.00, 1.11, 1.18 and 0.78 for blue UC emission, respectively. This is an indication that one-photon process is responsible for populating all blue, green and red UC emissions in Yb3+/Tm3+/Er3+:C12A7, which has been also found in Ho3+/Yb3+/Tm3+:LiNbO3 polycrystals under 980 nm excitation [16]. Here, one-photon process could be attributed to the competition between the linear decay and UC process for the depletion of the intermediate excited states [17].
This work was supported by the Guangdong Natural Science Funds for Distinguished young scholar (No.:2015A030306041), the tiptop Scientific and Technical Innovative Youth Talents of Guangdong special support program (No.:2015TQ01N060), the National Natural Science Foundation of China (No.:11304402), the link project of the National Natural Science Foundation of China and Guangdong Province (No.: U1401246), Act 211 Government of the RF (№ 02.A03.21.0006), NSFC-RFBR (Grant No. 1151101157/1 6-52-53059-UUEH_a) and Program of Presidium of RAS (No. 1517-2-20). References [1] F.Y. Xie, J.H. Li, Z.Y. Dong, D.W. Wen, J.X. Shi, J. Yan, M.M. Wu, RSC Adv. 5 (2015) 59830. [2] N. Kuganathan, H. Hosono, A.L. Shluger, P.V. Sushko, J. Am. Chem. Soc. 136 (2014) 2216–2219. [3] X.L. Liu, Y.X. Liu, D.T. Yan, H.C. Zhu, C.G. Liu, C.S. Xu, Y.C. Liu, X.J. Wang, J. Mater. Chem. 22 (2012) 16839–16843. [4] Y.Q. Mao, Y.P. Pu, J.F. Wei, Mater. Res. Inn. 15 (2011) 260–263. [5] Y.R. Yin, Z.T. Jia, W.X. Mu, Z.L. Gao, J. Zhang, X.T. Tao, Cryst. Growth Des. 16 (2016) 1903–1906. [6] P.V. Sushko, A.L. Shluger, K. Hayashi, M. Hirano, H. Hosono, Phys. Rev. Lett. 91 (2003) 126401–126404. [7] R.Q. Li, H.L. Xiong, Y.M. Liang, Y.L. Liu, N.N. Zhang, S.C. Gan, New J. Chem. 40 (2016) 1792–1798. [8] L. Liu, N.N. Zhang, Z.H. Leng, Y.M. Liang, R.Q. Li, L.C. Zou, S.C. Gan, Dalton Trans. 44 (2015) 6645–6654. [9] Y.F. Qu, R. Wang, Z.Z. Qiu, Y. Tao, J.J. Zhou, Opt. Mater. Express 5 (2015) 1881– 1889. [10] J.C. Sun, R. Wang, L.F. Wu, Z.Z. Qiu, L.L. Xing, Y.F. Qu, X.J. Ai, Sci. Adv. Mater. 4 (2012) 669–672. [11] D.Q. Chen, Y.L. Yu, F. Huang, H. Lin, P. Huang, A.P. Yang, Z.X. Wang, Y.S. Wang, J. Mater. Chem. 22 (2012) 2632–2640. [12] J.A. Damasco, G.Y. Chen, W. Shao, H. Ågren, H.Y. Huang, W.T. Song, J.F. Lovell, P. N. Prasad, ACS Appl. Mater. Interfaces 6 (2014) 13884–13893. [13] M.Y. Ding, D.Q. Chen, Z.Y. Wan, Y. Zhou, J.S. Zhong, J.H. Xi, Z.G. Ji, J. Mater. Sci. 50 (2015) 6779–6785. [14] K.Z. Zheng, Y. Liu, Z.Y. Liu, Z. Chen, W.P. Qin, Dalton Trans. 42 (2013) 5159– 5166. [15] J.S. Liao, L.L. Nie, S.H. Liu, B. Liu, H.R. Wen, J. Mater. Sci. 49 (2014) 6081–6086. [16] L.L. Xing, R. Wang, W. Xu, Y.N. Qian, Y.L. Xu, C.H. Yang, X.R. Liu, J. Lumin. 132 (2012) 1568–1574. [17] Y.N. Qian, B. Wang, R. Wang, L.L. Xing, Y.L. Xu, RSC Adv. 3 (2013) 13507–13514.