银岛膜对单个β-NaYF_4:Yb~(3+)/Er~(3+)晶体颗粒上转换荧光增强效应的研究
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摘要
采用水热法制备了六方相NaYF_4:Yb~(3+)/Er~(3+)(β-NaYF_4:Yb~(3+)/Er~(3+))微米晶体颗粒,并基于银岛膜(Ag film)衬底构建了一种Ag film/β-NaYF_4:Yb~(3+)/Er~(3+)微纳复合体系.通过扫描电子显微镜、场发射电子显微镜及X射线衍射仪对样品的形貌及晶体结构进行表征.实验结果表明,NaYF_4:Yb~(3+)/Er~(3+)微米晶体均为六方相晶体结构的六角盘.采用共焦显微测试系统,在980 nm激光激发下,系统研究了Ag film/β-NaYF_4:Yb~(3+)/Er~(3+)微纳复合体系中单个微米晶体上转换荧光强度与银岛膜的厚度依赖关系.结果发现:单颗粒β-NaYF_4:Yb~(3+)/Er~(3+)微米晶体的上转换荧光强度随着银岛膜的厚度增加而明显增大.根据理论推导及相应数值模拟得出,影响其荧光增强主要因素是由于银岛膜的反射效应和其表面附近的局域电磁场增强效应所导致.由此可见,构建这种新型结构可为增强单个微米颗粒的上转换荧光发射提供新的途径,为进一步拓展稀土微纳晶体的实际应用提供实验依据.
Rare-earth-doped upconversion(UC) is a nonlinear optical phenomenon in which the successive absorption of two or more low-energy photons via intermediate energy states leads to high-energy light emission(anti-Stokes emission). It endows their unique optical properties including low auto-fluorescence, high signal to noise ratio, a large anti-Stokes shift, and low toxicity. Therefore, rare-earth-doped UC materials have been widely used in photovoltaics, color displays,optical storages, biological imaging, and solar cells. However, the UC luminescence efficiency is much lower and largely limited the practical applications. The noble metal nanostructures as promised enhanced substrates could efficiently improve the intensity of UC luminescence and expand its applications. In this work, Yb~(3+)and Er~(3+)co-doped β-NaYF_4 microcrystals are synthesized via a simple and facile hydrothermal method with assistance of sodium citrate to control the crystal growth. Then, a Ag films/β-NaYF_4:Yb~(3+)/Er~(3+)hybrid structure that the β-NaYF_4:Yb~(3+)/Er~(3+)microcrystals were deposited on silver films with different thickness is constructed. The crystal phase and the morphology of the β-NaYF_4:Yb~(3+)/Er~(3+)microcrystals are analyzed with X-ray power diffraction(XRD), scanning electron microscope(SEM), and transmission electron microscopy(TEM). According to the results of XRD, SEM, and TEM, the pure hexagonal phased NaYF_4:Yb~(3+)/Er~(3+)are arc-shaped hexagonal plate microcrystals with smooth surface. The average overall dimension of each microcrystal is about 5.0 μm in diameter. The UC luminescence property of Ag film/β-NaYF_4:Yb~(3+)/Er~(3+)hybrid structure is investigated carefully by a confocal setup equipped with an optical microscope. When 980 nm continuous wave(CW) laser is focused on the central of a single microcrystal particle deposited on silver films with different thickness, the intensity of blue(2~H_(9/2)→4~I_(15/2)), green(4~S_(3/2)→4~I_(15/2) and2~H_(11/2)→4~_(I15/2)), and red(4~F_(9/2)→4~I_(15/2)) emission bands increases with increasing the Ag film thickness. The maximum enhancement factor(EF) for each emission band occurs at the Ag film thickness of 100 nm. But we realize that the intensity EF of each emission band is different, the EF for the green emission is greater than the blue and red one. A comprehensive analysis, based on the rate equations and the numerical calculation |E|~2, reveals that the optical reflection and local electric field enhancement effect of the Ag film play a role in the UC luminescence enhancement for the single β-NaYF_4:Yb~(3+)/Er~(3+)microcrystal. This finding breaks the limitation of conventional core-shell system, and it also provides a unique platform for micro-optoelectronic devices,solar energy conversion, optical sensors, and biological applications.
Rare-earth-doped upconversion(UC) is a nonlinear optical phenomenon in which the successive absorption of two or more low-energy photons via intermediate energy states leads to high-energy light emission(anti-Stokes emission). It endows their unique optical properties including low auto-fluorescence, high signal to noise ratio, a large anti-Stokes shift, and low toxicity. Therefore, rare-earth-doped UC materials have been widely used in photovoltaics, color displays,optical storages, biological imaging, and solar cells. However, the UC luminescence efficiency is much lower and largely limited the practical applications. The noble metal nanostructures as promised enhanced substrates could efficiently improve the intensity of UC luminescence and expand its applications. In this work, Yb~(3+)and Er~(3+)co-doped β-NaYF_4 microcrystals are synthesized via a simple and facile hydrothermal method with assistance of sodium citrate to control the crystal growth. Then, a Ag films/β-NaYF_4:Yb~(3+)/Er~(3+)hybrid structure that the β-NaYF_4:Yb~(3+)/Er~(3+)microcrystals were deposited on silver films with different thickness is constructed. The crystal phase and the morphology of the β-NaYF_4:Yb~(3+)/Er~(3+)microcrystals are analyzed with X-ray power diffraction(XRD), scanning electron microscope(SEM), and transmission electron microscopy(TEM). According to the results of XRD, SEM, and TEM, the pure hexagonal phased NaYF_4:Yb~(3+)/Er~(3+)are arc-shaped hexagonal plate microcrystals with smooth surface. The average overall dimension of each microcrystal is about 5.0 μm in diameter. The UC luminescence property of Ag film/β-NaYF_4:Yb~(3+)/Er~(3+)hybrid structure is investigated carefully by a confocal setup equipped with an optical microscope. When 980 nm continuous wave(CW) laser is focused on the central of a single microcrystal particle deposited on silver films with different thickness, the intensity of blue(2~H_(9/2)→4~I_(15/2)), green(4~S_(3/2)→4~I_(15/2) and2~H_(11/2)→4~_(I15/2)), and red(4~F_(9/2)→4~I_(15/2)) emission bands increases with increasing the Ag film thickness. The maximum enhancement factor(EF) for each emission band occurs at the Ag film thickness of 100 nm. But we realize that the intensity EF of each emission band is different, the EF for the green emission is greater than the blue and red one. A comprehensive analysis, based on the rate equations and the numerical calculation |E|~2, reveals that the optical reflection and local electric field enhancement effect of the Ag film play a role in the UC luminescence enhancement for the single β-NaYF_4:Yb~(3+)/Er~(3+)microcrystal. This finding breaks the limitation of conventional core-shell system, and it also provides a unique platform for micro-optoelectronic devices,solar energy conversion, optical sensors, and biological applications.
引文
1 Zhou B,Shi B,Jin D,et al.Controlling upconversion nanocrystals for emerging applications.Nat Nanotech,2015,10:924–936
2 Sun L D,Dong H,Zhang P Z,et al.Upconversion of rare earth nanomaterials.Annu Rev Phys Chem,2015,66:619–642
3 Gorris H H,Ali R,Saleh S M,et al.Tuning the dual emission of photon-upconverting nanoparticles for ratiometric multiplexed encoding.Adv Mater,2011,23:1652–1655
4 Auzel F.Upconversion and anti-Stokes processes with f and d ions in solids.Chem Rev,2004,104:139–174
5 Downing E,Hesselink L,Ralston J,et al.A three-color,solid-state,three-dimensional display.Science,1996,273:1185–1189
6 Shalav A,Richards B S,Trupke T,et al.Application of NaYF4:Er3+ up-converting phosphors for enhanced near-infrared silicon solar cell response.Appl Phys Lett,2005,86:013505
7 Sangeetha N M,Moutet P,Lagarde D,et al.3D assembly of upconverting NaYF4 nanocrystals by AFM nanoxerography:Creation of anticounterfeiting microtags.Nanoscale,2013,5:9587–9592
8 Zhang C,Zhou H P,Liao LY,et al.Luminescence modulation of ordered upconversion nanopatterns by a photochromic diarylethene:Rewritable optical storage with nondestructive readout.Adv Mater,2010,22:633–637
9 Wang Y,Wang H,Liu D,et al.Graphene oxide covalently grafted upconversion nanoparticles for combined NIR mediated imaging and photothermal/photodynamic cancer therapy.Biomaterials,2013,34:7715–7724
10 Gao W,Dong J,Wang R B,et al.Upconversion flourescence characteristics of Er3+/Yb3+ codoped NaYF4 and LiYF4microcrystals(in Chinese).Acta Phys Sin,2016,65:084205[高伟,董军,王瑞博,等.Er3+/Yb3+共掺NaYF4/LiYF4微米晶体的上转换荧光特性.物理学报,2016,65:084205]
11 Lin H,Xu D,Teng D,et al.Simultaneous size and luminescence control of NaYF4:Yb3+/RE3+(RE=Tm,Ho)microcrystals via Li+doping.Opt Mater,2015,45:229–234
12 Ma Y,Liu H,Han Z,et al.Raman scattering and plasmonic photocatalysis of single particles of NaYF4:Yb,Er@Ag under near-infrared laser excitation.Analyst,2014,139:5983–5988
13 Lee K T,ParkJ H,Kwon S J,et al.Simultaneous enhancement of upconversion and downshifting luminescence via plasmonic structure.Nano Lett,2015,15:2491–2497
14 He E,Zheng H,Zhang X,et al.Local-field effect on the fluorescence relaxation of Tm3+:LaF3 nanocrystals immersed in liquid medium.Luminescence,2009,13:66–70
15 Gao D L,Zheng H R,Tian Y,et al.Spectroscopic properties of Tm3+ and Ln3+(Ln3+=Yb3+,Er3+,Pr3+,Ho3+,Eu3+)co-dopes fluoride nanocrystals(in Chinese).Sci Sin-Phys Mech Astron,2010,40:287–295[高当丽,郑海荣,田宇,等.Tm3+和Ln3+(Ln3+=Yb3+,Er3+,Pr3+,Ho3+,Eu3+)共掺氟化物纳米晶体的光谱学性质.中国科学:物理学力学天文学,2010,40:287–295]
16 He E J,Moskovits M,Dong J,et al.Luminescence enhancement mechanism of lanthanide-doped hybrid nanostructures decorated by silver nanocrystals.Plasmonics,2015,10:357–368
17 Derom S,Berthelot A,Pillonnet A,et al.Metal enhanced fluorescence in rare earth doped plasmonic core-shell nanoparticles.Nanotechnology,2013,24:495704,arXiv:1312.6244
18 Feng A L,You M L,Tian L,et al.Distance-dependent plasmon-enhanced fluorescence of upconversion nanoparticles using polyelectrolyte multilayers as tunable spacers.Sci Rep,2015,5:7779
19 Liu S Y,Huang L,Li J F,et al.Simultaneous excitation and emission enhancement of fluorescence assisted by double plasmon modes of gold nanorods.J Phys Chem C,2013,117:10636–10642
20 Ming T,Chen H,Jiang R,et al.Plasmon-controlled fluorescence:Beyond the intensity enhancement.J Phys Chem Lett,2012,3:191–202
21 Dong J,Zhang Z,Zheng H,et al.Recent progress on plasmon-enhanced fluorescence.Nanophotonics,2015,4:472–490
22 Chen X,Xu W,Zhang L,et al.Large upconversion enhancement in the“islands”Au-Ag Alloy/NaYF4:Yb3+,Tm3+/Er3+ composite films,and fingerprint identification.Adv Funct Mater,2015,25:5462–5471
23 Han Q,Yan L,Zhang C,et al.Influence of Au nanoparticles on luminescence property of YF3submicrostructures doped with Yb3+ and Ho3+(Eu3+)ions.J Alloys Compd,2017,715:322–328
24 Schietinger S,Aichele T,Wang H Q,et al.Plasmon-enhanced upconversion in single NaYF4:Yb3+/Er3+ codoped nanocrystals.Nano Lett,2010,10 :134–138
25 Liu N,Qin W,Qin G,et al.Highly plasmon-enhanced upconversion emissions from Au@β-NaYF4:Yb,Tm hybrid nanostructures.Chem Commun,2011,47:7671–7673
26 Yin Z,Li H,Xu W,et al.Local field modulation induced three-order upconversion enhancement:Combining surface plasmon effect and photonic crystal effect.Adv Mater,2016,28:2518–2525
27 Sun Q C,Mundoor H,Ribot J C,et al.Plasmon-enhanced energy transfer for improved upconversion of infrared radiation in doped-lanthanide nanocrystals.Nano Lett,2014,14:101–106
28 Li C,Yang J,Quan Z,et al.Different microstructures ofβ-NaYF4fabricated by hydrothermal process:Effects of p H values and fluoride sources.Chem Mater,2007,19:4933–4942
29 Gao W,Zheng H,Han Q,et al.Unusual upconversion emission from single NaYF4:Yb3+/Ho3+ microrods under NIR excitation.Cryst Eng Comm,2014,16:6697–6706
30 Xu W,Xu S,Zhu Y,et al.Ultra-broad plasma resonance enhanced multicolor emissions in an assembled Ag/NaYF4:Yb,Er nano-film.Nanoscale,2012,4:6971–6973
31 Lu D,Cho S K,Ahn S,et al.Plasmon enhancement mechanism for the upconversion processes in NaYF4:Yb3+,Er3+ nanoparticles:Maxwell versus F?rster.ACS Nano,2014,8:7780–7792
2 Sun L D,Dong H,Zhang P Z,et al.Upconversion of rare earth nanomaterials.Annu Rev Phys Chem,2015,66:619–642
3 Gorris H H,Ali R,Saleh S M,et al.Tuning the dual emission of photon-upconverting nanoparticles for ratiometric multiplexed encoding.Adv Mater,2011,23:1652–1655
4 Auzel F.Upconversion and anti-Stokes processes with f and d ions in solids.Chem Rev,2004,104:139–174
5 Downing E,Hesselink L,Ralston J,et al.A three-color,solid-state,three-dimensional display.Science,1996,273:1185–1189
6 Shalav A,Richards B S,Trupke T,et al.Application of NaYF4:Er3+ up-converting phosphors for enhanced near-infrared silicon solar cell response.Appl Phys Lett,2005,86:013505
7 Sangeetha N M,Moutet P,Lagarde D,et al.3D assembly of upconverting NaYF4 nanocrystals by AFM nanoxerography:Creation of anticounterfeiting microtags.Nanoscale,2013,5:9587–9592
8 Zhang C,Zhou H P,Liao LY,et al.Luminescence modulation of ordered upconversion nanopatterns by a photochromic diarylethene:Rewritable optical storage with nondestructive readout.Adv Mater,2010,22:633–637
9 Wang Y,Wang H,Liu D,et al.Graphene oxide covalently grafted upconversion nanoparticles for combined NIR mediated imaging and photothermal/photodynamic cancer therapy.Biomaterials,2013,34:7715–7724
10 Gao W,Dong J,Wang R B,et al.Upconversion flourescence characteristics of Er3+/Yb3+ codoped NaYF4 and LiYF4microcrystals(in Chinese).Acta Phys Sin,2016,65:084205[高伟,董军,王瑞博,等.Er3+/Yb3+共掺NaYF4/LiYF4微米晶体的上转换荧光特性.物理学报,2016,65:084205]
11 Lin H,Xu D,Teng D,et al.Simultaneous size and luminescence control of NaYF4:Yb3+/RE3+(RE=Tm,Ho)microcrystals via Li+doping.Opt Mater,2015,45:229–234
12 Ma Y,Liu H,Han Z,et al.Raman scattering and plasmonic photocatalysis of single particles of NaYF4:Yb,Er@Ag under near-infrared laser excitation.Analyst,2014,139:5983–5988
13 Lee K T,ParkJ H,Kwon S J,et al.Simultaneous enhancement of upconversion and downshifting luminescence via plasmonic structure.Nano Lett,2015,15:2491–2497
14 He E,Zheng H,Zhang X,et al.Local-field effect on the fluorescence relaxation of Tm3+:LaF3 nanocrystals immersed in liquid medium.Luminescence,2009,13:66–70
15 Gao D L,Zheng H R,Tian Y,et al.Spectroscopic properties of Tm3+ and Ln3+(Ln3+=Yb3+,Er3+,Pr3+,Ho3+,Eu3+)co-dopes fluoride nanocrystals(in Chinese).Sci Sin-Phys Mech Astron,2010,40:287–295[高当丽,郑海荣,田宇,等.Tm3+和Ln3+(Ln3+=Yb3+,Er3+,Pr3+,Ho3+,Eu3+)共掺氟化物纳米晶体的光谱学性质.中国科学:物理学力学天文学,2010,40:287–295]
16 He E J,Moskovits M,Dong J,et al.Luminescence enhancement mechanism of lanthanide-doped hybrid nanostructures decorated by silver nanocrystals.Plasmonics,2015,10:357–368
17 Derom S,Berthelot A,Pillonnet A,et al.Metal enhanced fluorescence in rare earth doped plasmonic core-shell nanoparticles.Nanotechnology,2013,24:495704,arXiv:1312.6244
18 Feng A L,You M L,Tian L,et al.Distance-dependent plasmon-enhanced fluorescence of upconversion nanoparticles using polyelectrolyte multilayers as tunable spacers.Sci Rep,2015,5:7779
19 Liu S Y,Huang L,Li J F,et al.Simultaneous excitation and emission enhancement of fluorescence assisted by double plasmon modes of gold nanorods.J Phys Chem C,2013,117:10636–10642
20 Ming T,Chen H,Jiang R,et al.Plasmon-controlled fluorescence:Beyond the intensity enhancement.J Phys Chem Lett,2012,3:191–202
21 Dong J,Zhang Z,Zheng H,et al.Recent progress on plasmon-enhanced fluorescence.Nanophotonics,2015,4:472–490
22 Chen X,Xu W,Zhang L,et al.Large upconversion enhancement in the“islands”Au-Ag Alloy/NaYF4:Yb3+,Tm3+/Er3+ composite films,and fingerprint identification.Adv Funct Mater,2015,25:5462–5471
23 Han Q,Yan L,Zhang C,et al.Influence of Au nanoparticles on luminescence property of YF3submicrostructures doped with Yb3+ and Ho3+(Eu3+)ions.J Alloys Compd,2017,715:322–328
24 Schietinger S,Aichele T,Wang H Q,et al.Plasmon-enhanced upconversion in single NaYF4:Yb3+/Er3+ codoped nanocrystals.Nano Lett,2010,10 :134–138
25 Liu N,Qin W,Qin G,et al.Highly plasmon-enhanced upconversion emissions from Au@β-NaYF4:Yb,Tm hybrid nanostructures.Chem Commun,2011,47:7671–7673
26 Yin Z,Li H,Xu W,et al.Local field modulation induced three-order upconversion enhancement:Combining surface plasmon effect and photonic crystal effect.Adv Mater,2016,28:2518–2525
27 Sun Q C,Mundoor H,Ribot J C,et al.Plasmon-enhanced energy transfer for improved upconversion of infrared radiation in doped-lanthanide nanocrystals.Nano Lett,2014,14:101–106
28 Li C,Yang J,Quan Z,et al.Different microstructures ofβ-NaYF4fabricated by hydrothermal process:Effects of p H values and fluoride sources.Chem Mater,2007,19:4933–4942
29 Gao W,Zheng H,Han Q,et al.Unusual upconversion emission from single NaYF4:Yb3+/Ho3+ microrods under NIR excitation.Cryst Eng Comm,2014,16:6697–6706
30 Xu W,Xu S,Zhu Y,et al.Ultra-broad plasma resonance enhanced multicolor emissions in an assembled Ag/NaYF4:Yb,Er nano-film.Nanoscale,2012,4:6971–6973
31 Lu D,Cho S K,Ahn S,et al.Plasmon enhancement mechanism for the upconversion processes in NaYF4:Yb3+,Er3+ nanoparticles:Maxwell versus F?rster.ACS Nano,2014,8:7780–7792