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构建核壳结构可有效降低材料的表面缺陷及实现掺杂离子的可控区域分布, 已成为目前增强及调控材料发光特性的有效手段之一. 为此, 本文以外延生长技术, 构建了一系列NaLnF4 (Ln = Y, Yb, Ho)@ NaLnF4 (Ln = Y, Yb)核壳微米结构, 并实现了Ho3+离子上转换发光的增强及可控调节. 借助共聚焦显微光谱测试系统, 在980 nm近红外激光激发下, 研究Ho3+离子在不同单颗粒核壳结构中的上转换发光特性. 结果表明, 当包覆NaYF4惰性壳时, NaYF4:Yb3+/Ho3+及NaYbF4:Ho3+ 微米棒的上转换发射强度均得到了明显增强, 而NaHoF4@NaYF4微米核壳结构的发射强度却没有发生明显的变化. 当在其NaYF4惰性壳中引入Yb3+离子时, NaYF4:Yb3+/Ho3+, NaYbF4:Ho3+及NaHoF4 微米核壳结构的发射强度及红绿比均再次得到了明显增强. 基于对其光谱特性及动力学过程的研究, 其发射增强主要由于壳层中的Yb3+离子通过能量迁移及传递过程有效地提高Ho3+离子激发, 进而在双向协同的作用下实现其发光有效增强及色彩调控. 由此可见, 对于微米晶体而言, 构建其不同的核壳结构不仅可实现其发光有效增强, 且可根据掺杂离子的不同及其区域分布实现光谱的精准调控, 为拓展高效发光特性的微米晶体在防伪、微纳光电器件等领域的应用提供新途径.Constructing core-shell structures can effectively reduce the surface quenching effect of luminescent materials, which becomes an effective method to enhance upconversion luminescence. In this work, a series of NaLnF4@NaLnF4 (Ln = Y3+, Yb3+, Ho3+) core-shell microcrystals is successfully synthesized based on epitaxial growth technology, thereby enhancing and regulating the upconversion emission of Ho3+ ions. The results of the XRD and SEM indicate that the NaLnF4@NaLnF4 core-shell microcrystal possesses a pure hexagonal-phase crystal structure with a rod-like shape. Meanwhile, it is found that the epitaxial growth direction of the micro-shell is not affected by the crystal characteristics in the core, but determined by the crystal characteristics of the shell. Under 980 nm near-infrared laser excitation, the upconversion luminescence properties of single microrods with different core-shell structures are investigated via a confocal microscope spectroscopy. It is found that in the NaLnF4 micro-crystal, the coated NaYF4 inert shell can also effectively reduce the quenching effect on the surface of the micro-crystal for enhancing upconversion emission. When the Yb3+ ions are introduced into NaYF4 or NaYbF4 active shell that is coated, the Yb3+ ions in the shell can effectively transfer excitation energy to Yb3+ in the core through energy migration, and then establish new energy transfer channels, thereby realizing the Ho3+ ion luminescence enhancement. For NaHoF4@NaYbF4 core-shell microrods, the Yb3+ in the shell can transfer more excitation energy to Ho3+ ions at the adjacent interface for enhancing the overall luminescence intensity, and its higher red-green ratio is mainly due to the cross-relaxation process occurring between the Ho3+ ions at high doping concentration of Ho3+ in the NaHoF4 core. Meanwhile, the luminescence process of the micron core-shell system is further confirmed based on the luminescence characteristics of different structures and the dynamic luminescence process. It can be seen that constructing different micron core-shell structures and introducing sensitizing ions, can not only effectively enhance the luminous intensity of the micron materials, but also adjust the output color. Therefore, this research is an important experimental reference for enhancing the luminous intensity of the micron system and the precise adjustment of luminescence, and can effectively expand the applications of micron crystals in the fields of displays, micron lasers and anti-counterfeiting.
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Keywords:
- upconversion luminescence /
- micron core-shell structure /
- luminescence regulation /
- energy transfer /
- single particle
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图 1 NaYF4:20%Yb3+/2%Ho3+与NaHoF4微米晶体及其相应核壳结构的XRD图谱
Fig. 1. The XRD patterns of NaYF4:20%Yb3+/2%Ho3+ microcrystals and NaHoF4 microcrystals with corresponding core-shell (CS) microcrystals.
图 2 (a)—(f) NaYF4:20%Yb3+ /2%Ho3+ 及(a1)—(c1) NaHoF4包覆不同壳层结构微米棒的SEM及其相应的mapping图
Fig. 2. The SEM images and element mappings of Y, Yb, Ho of (a)–(f) NaYF4: 20%Yb3+ /2%Ho3+ microrods and (a1)–(c1) NaHoF4 microrods with corresponding CS microrods.
图 3 共聚焦显微光谱测试装置示意图(M1, M2, 半透半反镜; L1, L2, 透镜)
Fig. 3. Schematic illustration of confocal microscopy setup (M1, M2, semi-transparent and semi-reflective mirrors; L1, L2, lenses).
图 4 在980 nm激发下, 单个NaYF4:20%Yb3+/2%Ho3+及其核壳微米棒的(a)上转换发射光谱, (b)蓝光、绿光和红光的发射峰面积, (c)红绿比和(d) CIE 色度坐标图
Fig. 4. (a) The UC emission spectra, (b) the peak area of the bule, green and red emission intensity, (c) R/G ratio and (d) CIE chromaticity diagram of the single NaYF4:20%Yb3+/2%Ho3+ microrod with corresponding CS microrod under the excitation of a 980 nm near-infrared (NIR) laser.
图 5 在980 nm激光激发下, (a) 单颗粒NaYbF4:2%Ho3+ 和(b) NaHoF4微米棒及其相应核壳微米棒的上转换(UC)发射光谱(插图为其相应的红绿比及发光照片)
Fig. 5. The UC emission spectra of the single (a) NaYbF4:2%Ho3+ and (b) NaHoF4 microrod with corresponding CS microrod under the excitation of a 980 nm NIR laser (The insert is corresponding optical micrographs and R/G ratio).
图 6 在980 nm激光激发下, Ho3+离子与Yb3+离子在不同核壳微米结构中的能量传递与其可能的辐射及无辐射跃迁过程 (a) NaYF4:20%Yb3+/2%Ho3+@NaYF4微米核壳结构; (b) NaHoF4@NaYbF4 微米核壳结构
Fig. 6. Possible energy transfer, radiation and no-radiation processes between Yb3+ and Ho3+, in the (a) NaYF4:20%Yb3+/2%Ho3+@NaYF4 and (b) NaHoF4@NaYbF4 CS structures
图 7 单颗粒微米棒与泵浦功率的依赖关系 (a), (b) NaYF4:20%Yb3+/2%Ho3+微米棒; (c), (d) NaYF4:20%Yb3+/2%Ho3+@NaYF4:40%Yb3+核壳微米棒; (e), (f) NaYbF4:2%Ho3+@NaYF4核壳微米棒
Fig. 7. Pump power dependences of the single-particle microrod: (a), (b) NaYF4:20%Yb3+/2%Ho3+ microrod; (c), (d) NaYF4:20%Yb3+/2%Ho3+@NaYF4 CS microrod; (e), (f) NaYbF4:2%Ho3+@NaYF4 CS microrod.
图 8 在 980 nm脉冲激光激发下, 不同的(a), (b) NaYF4及(c), (d) NaHoF4核壳微米棒中Ho3+离子5F5能级(b), (d)及其5S2能级(a), (c)的辐射衰减寿命曲线图
Fig. 8. Decay curves of the (b), (d) 5F5 and (a), (c) 5S2 levels in (a), (b) NaYF4 and (c), (d) NaHoF4 microrod with corresponding CS microrods under the excitation of a 980 nm NIR pulse laser.
表 1 水热法制备微米晶体所需药品的详细参数
Table 1. Detailed parameters of the chemical reagents required for the preparation of microcrystals by hydrothermal method.
样品 EDTA
/gRE(NO3)3/
mmolNaF/
mmolNH4HF2/mmol NaYF4:20%Yb3+/
2%Ho3+0.282 0.75 2.5 3 NaYbF4:2%Ho3+ 0.282 0.75 2.5 3 NaHoF4 0.282 0.75 2.5 3 
下载: 导出CSV
表 2 水热法制备微米核壳晶体的所需药品的详细参数
Table 2. Detailed parameters of the chemical reagents required for the preparation of the core-shell microcrystal by hydrothermal method.
样品 Seed crystals quality/g EDTA/mmol RE(NO3)3/mmol NaF/mmol NH4HF2/mmol NaYF4:20%Yb3+/2%Ho3+@NaYF4 0.1494 0.75 0.75 2.5 3 NaYF4:20%Yb3+/2%Ho3+@NaYbF4 0.1494 0.75 0.75 2.5 3 NaYbF4:2%Ho3+@NaYF4 0.1228 0.75 0.50 2.5 3 NaHoF4@NaYF4 0.1995 0.75 0.75 2.5 3 NaHoF4@NaYF4:20%Yb3+ 0.1995 0.75 0.75 2.5 3 NaHoF4@NaYbF4 0.1995 0.75 0.75 2.5 3
下载: 导出CSV
表 3 在980 nm 脉冲激发光下, NaYF4与NaHoF4核壳微米棒核壳纳米晶体中的Ho3+离子5F5能级及5S2能级的辐射寿命值
Table 3. Luminescence lifetimes of the 5F5 and 5S2 levels in NaYF4 and NaHoF4 microrod with corresponding CS microrods under the excitation of a 980 nm NIR pulse laser.
Samples Lifetime/μs 5S2: 541 nm 5F5: 645 nm NaYF4:20%Yb3+/2%Ho3+ 201.3 367.7 NaYF4:20%Yb3+/2%Ho3+@
NaYF4298.6 445.1 NaYF4:20%Yb3+/2%Ho3+@
NaYF4:20%Yb3+380.4 529.3 NaYF4:20%Yb3+/2%Ho3+@
NaYF4:40%Yb3+472.3 682.1 NaYF4:20%Yb3+/2%Ho3+@
NaYF4:80%Yb3+416.5 573.4 NaHoF4@NaYF4:20%Yb3+ 167.4 247.3 NaHoF4@NaYbF4 236.6 318.6
下载: 导出CSV
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[1] Deng R R, Qin F, Chen R F, Huang W, Hong M H, Liu X G 2015 Nat. Nanotechnol. 10 237
Google Scholar
[2] Gong G, Song Y, Tan H H, Xie S W, Zhang C F, Xu L J, Xu J X, Zheng J 2019 Compos. Part B-Eng. 179 107504
Google Scholar
[3] Park Y I, Lee K T, Suh Y D, Hyeon T H 2015 Chem. Soc. Rev. 44 1302
Google Scholar
[4] Zheng W, Huang P, Tu D T, Ma E, Zhu H M, Chen X Y 2015 Chem. Soc. Rev. 44 1379
Google Scholar
[5] Wang J, Wei T, Li X Y, Zhang B H, Wang J X, Huang C, Yuan Q 2014 Angew. Chem. 126 1642
Google Scholar
[6] Wang Y H, Ohwaki. J 1993 Appl. Phys. Lett. 63 3268
Google Scholar
[7] Rakov N, Maciel G S, Sundheimer M L, Menezes L D S, Gomes A S L, Messaddeq Y, Cassanjes F C, Poirier G, Ribeiro S J L 2002 J. Appl. Phys. 92 6337
Google Scholar
[8] Su Q Q, Han S Y, Xie X J, Zhu H M, Chen H Y, Chen C K, Liu R S, Chen X Y, Wang F, Liu X G 2012 J. Am. Chem. Soc. 134 20849
Google Scholar
[9] Wang Y D, Yang Z W, Ma Y J, Chai Z Z, Qiu J B, Song Z G 2017 J. Mater. Chem. C 5 8535
Google Scholar
[10] Dong J, Gao W, Han Q Y, Wang Y K, Qi J X, Yan X W, Sun M T 2019 Rev. Phys. 4 100026
Google Scholar
[11] Tian Q, Tao K, Sun K 2013 Micro Nano Lett. 8 731
Google Scholar
[12] Homann C, Krukewitt L, Frenzel F, Grauel B, Würth C, Resch-Genger U, Haase M 2018 Angew. Chem. Int. Ed. 57 8765
Google Scholar
[13] Choi J E, Kim D, Jang H S 2019 Chem. Commun. 55 2261
Google Scholar
[14] Ju D D, Song F, Han Y D, Zhang J, Song F F, Zhou A H, Huang W, Zadkov V 2019 J. Alloy. Compd. 787 1120
Google Scholar
[15] Jiao X F, Ye W H, Huang Q Y, Luo J, Yu L L, Liu X T 2020 J. Rare Earth 38 697
Google Scholar
[16] Gao W, Sun Z Y, Han Q Y, Han S S, Cheng X T, Wang Y K, Yan X W, Dong J 2021 J. Alloy. Compd. 857 157578
Google Scholar
[17] Gai S L, Li C X, Yang P P, Lin J 2014 Chem. Rev. 114 2343
Google Scholar
[18] Gao W, Zheng H R, Han Q Y, He E J, Wang R B 2014 CrystEngComm. 16 6697
Google Scholar
[19] 高伟, 王博扬, 孙泽煜, 高露, 张晨雪, 韩庆艳, 董军 2020 物理学报 69 034207
Google Scholar
Gao W, Wang B Y, Sun Z Y, Gao L, Zhang C X, Han Q Y, Dong J 2020 Acta Phys Sin 69 034207
Google Scholar
[20] Gao D L, Zhang X Y, Gao W, 2013 ACS Appl. Mat. Inter. 5 9732
Google Scholar
[21] Zhang Y H, Huang L, Liu X G 2016 Angew. Chem. Int. Ed. 55 5718
Google Scholar
[22] Chen B, Sun T Y, Qiao X S, Fan X P, Wang F 2015 Adv. Opt. Mater. 3 1577
Google Scholar
[23] Tong L M, Lu E, Pichaandi J, Zhao G Y, Winnik M A 2016 J. Phys. Chem. C 120 6269
[24] Zhang Y H, Huang L, Liu X G, 2016 Angew. Chem. 128 5812
Google Scholar
[25] 董军, 张晨雪, 程小同, 邢宇, 韩庆艳, 严学文, 祁建霞, 刘继红, 杨祎, 高伟 2021 物理学报 70 154208
Google Scholar
Dong J, Zhang C X, Cheng X T, Xing Y, Han Q Y, Yan X W, Qi J X, Liu J H, Yang Y, Gao W 2021 Acta Phys. Sin. 70 154208
Google Scholar
[26] Gao W, Zheng H R, Han Q Y, He E J, Gao F Q, Wang R B 2014 J. Mater. Chem. C 2 5327
Google Scholar
[27] Sangeetha N M, van Veggel F C J M 2009 J. Phys. Chem. C 113 14702
Google Scholar
[28] Pilch A, Würth C, Kaiser M, Wawrzyńczyk D, Kurnatowska M, Arabasz S, Prorok K, Samoć M, Strek W, Resch-Genger U, Bednarkiewicz A 2017 Small 13 1701635
Google Scholar
[29] Gao W, Kong X Q, HanQ Y, ChenY, ZhangJ, Zhao X, Yan X W, Liu J H, Shi J, Dong J 2018 J. Lumin. 202 381
Google Scholar
[30] Gao D L, Zhang X Y, Zheng H R, Gao W, He E J, 2013 J. Alloy. Compd. 554 395
Google Scholar
[31] Shi F, Wang J S, Zhai X S, Zhao D, Qin W P, 2011 CrystEngComm 13 3782
Google Scholar
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Google Scholar
[33] Auzel F 2004 Chem. Rev 104 139
Google Scholar
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