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本文主要以具有六方相结构的NaLuF4:Yb3+/Ho3+/Ce3+纳米晶体为核, 采用外延生长法构建具有同质结构的NaLuF4:Yb3+/Ho3+/Ce3+@NaLuF4:Yb3+核壳纳米晶体. 借助X-射线衍射仪及透射电子显微镜对样品的晶体结构、形貌及尺寸进行表征. 在近红外光980 nm激光激发下, 通过构建核壳结构及有效调控外壳中敏化离子Yb3+离子的掺杂浓度, 实现Ho3+离子在NaLuF4纳米晶体中的红光发射增强. 实验结果表明: 在相同的激发条件下, 具有核壳结构的NaLuF4:Yb3+/Ho3+/Ce3+@NaLuF4:Yb3+纳米晶体的红光发射均得到了增强, 同时, 当外壳中Yb3+离子的掺杂浓度为10.0%时, 其上转换红光发射强度最强, 为NaLuF4:Yb3+/Ho3+/Ce3+晶体核红光发射强度的5.8倍. 根据其光谱特性及发光动力学过程, 讨论了同质壳及壳中敏化离子掺杂浓度变化对其发光特性的影响规律. 这种具有较强红光发射的核壳结构纳米晶体在生物医学、防伪编码、多色显示等领域具有较大的应用前景.
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关键词:
- NaLuF4纳米晶体 /
- 核壳结构 /
- 上转换发光 /
- 荧光增强
A series of the hexagonal-phase NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0% Ce3+@NaLuF4:x%Yb3+ core-shell (CS) nanocrystals with codoping different Yb3+ ions in the shell is successfully built by a sequential growth process. The crystal structures and morphologies of samples are characterized by X-ray diffractometer and transmission electron microscope. With the Yb3+ ion concentration increasing from 0% to 15% in NaLuF4 shell, none of the crystal structures, sizes, and morphologies of the samples changes obviously because of the similarity in ionic radius between Yb3+ and the ions in shell and the low doping concentration. Under 980 nm near-infrared (NIR) excitation, the NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+ core nanocrystal produce green and red UC emission. And the red UC emission intensity is higher than green emission intensity. This is because two effective cross-relaxation processes happen between Ho3+ and Ce3+ ions, which results in the enhancement of the red emission. However, the overall emission intensity of NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+ nanocrystal decrease compared with that of the NaLuF4:20.0%Yb3+/2.0%Ho3+ nanocrystal. Thus, to further enhance the red UC emission intensity in NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+ nanocrystal, the NaLuF4:20.0%Yb3+/2.0% Ho3+/12.0%Ce3+@NaLuF4:x%Yb3+ CS nanocrystal are prepared for blocking the excitation and emission energy, transmitting surface quenching center and getting more excitation energy through doping Yb3+ ions in NaLuF4 shell. It can be clearly seen that the red UC emission intensity of CS nanocrystal first increases and then decreases with Yb3+ ion concentration increasing. Meanwhile, the corresponding red-to-green ratio increases from 4.9 to 5.6. The highest red UC emission intensity is observed in each of the NaLuF4:20.0%Yb3+ /2.0%Ho3+/12.0%Ce3+@NaLuF4:10%Yb3+ CS nanocrystal because the Ho3+ ions get more energy through the following three ways: 1) Yb3+ (core)-Ho3+ (core); 2) Yb3+ (shell)-Ho3+ (core); 3) Yb3+ (shell)-Yb3+ (core)-Ho3+ (core). Thus, building CS nanocrystals is one of the most effective approaches in order to improve the UC efficiency by suppressing the non-radiative decay of activators in the core and getting more excitation energy through different energy transfer ways. These NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@NaLuF4:Yb3+ CS nanocrystals with red UC emission have great potential applications in biological field and multi-primary color.-
Keywords:
- NaLuF4 nanocrystals /
- core-shell /
- upconversion emission /
- fluorescent enhancement
[1] Menyuk N, Dwight K, Pinaud F 1972 Appl. Phys. Lett. 21 159Google Scholar
[2] Downing E, Hesselink L, Ralston J, Macfarlane R A 1996 Science 273 1185Google Scholar
[3] Zhang Y, Zhang L, Deng R, Tian J, Zong Y, Jin D, Liu X G 2014 J. Am. Chem. Soc. 136 4893Google Scholar
[4] Zou W, Visser C, Maduro J A, Pshenichnikov M S, Hummelen J C 2012 Nat. Photon. 6 560Google Scholar
[5] Su Q, Feng W, Yang D, Li F 2017 Acc. Chem. Res. 50 32Google Scholar
[6] Huang B L, Dong H, Wong K L, Sun L D, Yan C H 2016 J. Phys. Chem. C 120 18858Google Scholar
[7] Niu N, Yang P P, He F, Zhang X, Gai S L, Li C X, Lin J 2012 J. Mater. Chem. 2 2
[8] 高当丽, 郑海荣, 田宇, 雷瑜, 崔敏, 何恩节, 张喜生 2010 中国科学: 物理学 力学 天文学 40 287
Gao D L, Zheng H R, Tian Y, Lei Y, Cui M, He E J, Zhang X S 2010 Sci. Sin.: Phys. Mech. Astron. 40 287
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He E J, Zheng H R, Gao W, Lu Y, Li J N, Wei Y, Wang D, Zhu G Q 2013 Acta Phys. Sin. 62 237803Google Scholar
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Gao W, Dong J 2017 Acta Phys. Sin. 66 204206Google Scholar
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图 1 (a) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+纳米晶体核, (b)−(e) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4:x%Yb3+(x = 0%, 5.0%, 10.0%, 15.0%)纳米核壳结构的XRD图谱
Fig. 1. XRD patterns of (a) NaLuF4:20.0%Yb3+ /2.0%Ho3+/12.0%Ce3+ nanocrystals and (b)−(e) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4:x%Yb3+(x = 0%, 5.0%, 10.0%, 15.0%) core-shell nanocrystals.
图 2 (a) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+纳米晶体和NaLuF4:20.0%Yb3+/2.0%Ho3+/12%Ce3+@ NaLuF4:x%Yb3+((b) 0, (c) 5.0%, (d)10.0%, (e) 15.0%)纳米核壳结构的TEM图谱
Fig. 2. TEM images and EDX spectra of (a) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+ nanocrystals and (b)−(e) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4: x%Yb3+ (x = 0, 5.0%, 10.0%, 15.0%) core-shell nanocrystals.
图 3 在980 nm激发下, (a) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+和(b)−(e) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4:x%Yb3+ (x = 0%, 5.0%, 8.0%,10.0%, 12.0%, 15.0%)纳米晶体及核壳结构的上转换发射光谱(A)、增强因子(B)和红绿比(C)
Fig. 3. The upconverison emission spectra (A), enhancement factor (B) and red andgreen emission intensity ratio (R/G) (C) of (a) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+ nanocrystals and (b)−(e) NaLuF4:20.0%Yb3+/2.0%Ho3+/12%Ce3+@ NaLuF4:x%Yb3+ (x = 0%, 5.0%, 8.0%, 10.0%, 12.0%,15.0%) core-shell nanocrystals under 980 nm excitation.
图 4 (a) NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+以及(b)—(e)NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@NaLuF4:x%Yb3+ (x = 0%, 5.0%, 10.0%, 15.0%) 纳米晶体及核壳结构的色度坐标图
Fig. 4. The CIE diagram with position of color coordinates of Ho3+ in (a) NaLuF4 nanocrystals and (b)-(e) NaLuF4@ NaLuF4:x%Yb3+ (x = 0%, 5.0%, 10.0%, 15.0%) core-shell nanocrystals.
表 1 NaLuF4和NaLuF4@NaLuF4核壳纳米晶体的的CIE色坐标
Table 1. The calculated CIE chromaticity coordinates (x, y) of Ho3+ in NaLuF4 nanocrystals and NaLuF4@ NaLuF4:x%Yb3+ (x = 0%, 5.0%, 10.0%, 15.0%) core-shell nanocrystals.
Samples CIE chromaticity coordinates x y a (NaLuF4:20.0%Yb3+/2.0%Ho3+ /12.0%Ce3+) 0.5501 0.3891 b (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4) 0.5621 0.3786 c (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4: 5.0%Yb3+) 0.5643 0.3727 d (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4: 10.0%Yb3+) 0.5724 0.3692 e (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4: 15.0%Yb3+) 0.5756 0.3599 表 2 NaLuF4和NaLuF4@ NaLuF4核壳纳米晶体的红光发射的荧光寿命
Table 2. Luminescence lifetimes of NaLuF4 and NaLuF4@NaLuF4 core-shell nanocrystals under 980 nm excitation at 650 nm
Samples Lifetime/μs 650 nm a (NaLuF4:20.0%Yb3+/2.0%Ho3+ 12.0%Ce3+) 97.4 ± 0.2 b (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4) 125.4 ± 1.1 c (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4:5.0%Yb3+) 136.3 ± 0.8 d (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4:10.0%Yb3+) 184.2 ± 0.6 e (NaLuF4:20.0%Yb3+/2.0%Ho3+/12.0%Ce3+@ NaLuF4:15.0%Yb3+) 144.4 ± 0.4 -
[1] Menyuk N, Dwight K, Pinaud F 1972 Appl. Phys. Lett. 21 159Google Scholar
[2] Downing E, Hesselink L, Ralston J, Macfarlane R A 1996 Science 273 1185Google Scholar
[3] Zhang Y, Zhang L, Deng R, Tian J, Zong Y, Jin D, Liu X G 2014 J. Am. Chem. Soc. 136 4893Google Scholar
[4] Zou W, Visser C, Maduro J A, Pshenichnikov M S, Hummelen J C 2012 Nat. Photon. 6 560Google Scholar
[5] Su Q, Feng W, Yang D, Li F 2017 Acc. Chem. Res. 50 32Google Scholar
[6] Huang B L, Dong H, Wong K L, Sun L D, Yan C H 2016 J. Phys. Chem. C 120 18858Google Scholar
[7] Niu N, Yang P P, He F, Zhang X, Gai S L, Li C X, Lin J 2012 J. Mater. Chem. 2 2
[8] 高当丽, 郑海荣, 田宇, 雷瑜, 崔敏, 何恩节, 张喜生 2010 中国科学: 物理学 力学 天文学 40 287
Gao D L, Zheng H R, Tian Y, Lei Y, Cui M, He E J, Zhang X S 2010 Sci. Sin.: Phys. Mech. Astron. 40 287
[9] Gao W, Zheng H R, He E J, Lu Y, Gao F Q 2014 J. Lumin. 152 44Google Scholar
[10] Teng X, Zhu Y H, Wei W, Wang S C, Huang J F, Naccache R, Hu W B, Tok A I Y, Han Y, Zhang Q C, Fan Q L, Huang W, Capobianco J A, Huang L 2012 J. Am. Chem. Soc. 134 8340Google Scholar
[11] Heer S, Kompe K, Gudel H U, Haase M 2004 Adv. Mater. 16 2102Google Scholar
[12] Mai H X, Zhang Y W, Sun L D, Yan C H 2007 J. Phys. Chem. C 111 13721Google Scholar
[13] Shi F, Wang J S, Zhai X S, Zhao D, Qin W P 2011 Cryst. Eng. Comm. 13 3782Google Scholar
[14] Yang T S, Sun Y, Liu Q, Feng W, Yang P Y, Li F Y 2012 Biomaterials 33 3733Google Scholar
[15] He E J, Zheng H R, Gao W, Tu Y X, Lu Y, Li G A 2013 Mater. Res. Bull. 48 3505Google Scholar
[16] Chang J, Liu Y, Li J, Wu S L, Niu W B, Zhang S F 2013 J. Mater. Chem. C 1 1168Google Scholar
[17] Gao D L, Zhang X Z, Zheng H R, Gao W, He E J 2013 J. Alloy. Compd. 554 395Google Scholar
[18] Gao W, Zheng H R, Han Q Y, He E J, Gao F Q, Wang R B 2014 J. Mater. Chem. C 2 5327Google Scholar
[19] 何恩节, 郑海荣, 高伟, 鹿盈, 李俊娜, 魏映, 王灯, 朱刚强 2013 物理学报 62 237803Google Scholar
He E J, Zheng H R, Gao W, Lu Y, Li J N, Wei Y, Wang D, Zhu G Q 2013 Acta Phys. Sin. 62 237803Google Scholar
[20] Dong J, Gao W, Han Q Y, Wang Y K, Qi J X, Yan X W, Sun M T 2019 Rev. Phys. 4 100026Google Scholar
[21] Dong J, Zhang Z L, Zheng H R, Sun M T 2015 Nanophotonics 4 472
[22] Li Y, Wang G F, Pan K, Fan N Y, Liu S, Feng L 2013 RSC Adv. 3 1683Google Scholar
[23] Rai M, Singh S K, Singh A K, Prasad R, Koch B, Mishra K, Rai S B 2015 ACS Appl. Mater. Inter. 7 15339Google Scholar
[24] Zuo J, Li Q Q, Xue B, Li C X, Chang Y L, Zhang Y L, Liu X M, Tu L P, Zhang H, Kong X G 2017 Nanoscale 9 7941Google Scholar
[25] Yi G S, Lu H C, Zhao S Y, Ge Y, Yang W J, Chen D P, Guo L H 2004 Nano Lett. 4 2191Google Scholar
[26] Chen X, Peng D, Ju Q, Wang F 2015 Chem. Soc. Rev. 44 1318Google Scholar
[27] Gao W, Dong J, Liu J H, Yan X W 2016 Mater. Res. Bull. 80 256Google Scholar
[28] 高伟, 董军 2017 物理学报 66 204206Google Scholar
Gao W, Dong J 2017 Acta Phys. Sin. 66 204206Google Scholar
[29] Hu H, Chen Z G, Cao T Y, Zhang Q, Yu M G, Li F Y, Yi T, Huang C H 2008 Nanotechnology 19 375702Google Scholar
[30] Sangeetha N M, van Veggel F C J M 2009 J. Phys. Chem. C 113 14702Google Scholar
[31] Ye S, Chen G Y, Shao W, Junle Q, Paras N P 2015 Nanoscale 7 3976Google Scholar
[32] Xie X G, Ga N G, Deng R R, Sun Q, Xu Q H, Liu X G 2013 J. Am. Chem. Soc. 135 12608Google Scholar
[33] Wang F, Deng R R, Wang J, Wang Q X, Han Y, Zhu H M, Chen X Y, Liu X G 2011 Nat. Mater. 10 968Google Scholar
[34] Vetrone B F, Naccache R, MahalingamV, Morgan C G, Capobianco J A 2009 Adv. Funct. Mater. 19 2924Google Scholar
[35] Gao W, Kong X Q, Han Q Y, Dong J, Zhang W W, Zhang B, Yan X W, Zhang Z L, He E J, Zheng H R 2018 J. Lumin. 196 186
[36] Dong J, Zhang J, Han Q Y, Zhao X, Yan X W, Liu J H, Ge H B, Gao W 2019 J. Lumin. 207 361Google Scholar
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