應用低折射率導模共振光柵結構提升稀土奈米粒子之上轉換螢光訊號

Guided-mode resonance enhanced near-infrared-to-visible up-conversion fluorescence with a low-refractive index resonant waveguide grating

邱顯文(HSIEN-WEN CHIU)

指導教授 ： 許佳振

國立中正大學/理學院/物理學系/碩士(2016年)

摘要

本研究利用一維低折射率導模共振光柵結構(resonant waveguide grating, RWG)提升能量上轉換稀土(rare earth, RE)螢光材料的螢光增益，將長波長低能量激發光轉換成短波長高能量放射光。導模共振光柵結構是利用玻璃基板上旋轉塗佈多層含有多孔隙二氧化矽(SiO2)低折射率(n=1.22)薄膜的一維光柵層，光柵層上濺鍍高折射率材料(TiO2)為波導層，在波導層表面上利用浸塗法(dip-costing)均勻塗佈上轉換稀土螢光奈米粒子(NaYF4:Yb3+,Tm3+)，最後用水覆蓋封裝。實驗中，當入射激發光雷射(波長976 nm)耦合導模共振光柵TE模態，激發共振(excitation resonance)發生時，可提升上轉換螢光訊號達約10^4倍，若出射螢光再符合耦合條件時，可產生萃取共振(extraction resonance)再提升上轉換螢光訊號約1.5~2倍。利用嚴格耦合波理論(rigorous coupled-wave analysis, RCWA)模擬計算得知，激發共振產生時，TiO2波導層和水的介面形成局部強場分佈，使得光柵結構表面形成很強的電場強度來提升螢光訊號。因低折射率光柵層與TiO2波導層表面水溶液之折射率較為接近，達到較高的折射率對稱性使得強電場位置靠近上轉換螢光奈米粒子，故可大幅提升上轉換螢光強度。此種低折射率材料導模共振光柵結構將可用於螢光顯微鏡的生醫感測元件，使得應用的層面更加廣泛。
關鍵字：低折射率、能量上轉換、稀土、螢光、導模共振

關鍵字

導模共振 ； 螢光 ； 稀土 ； 能量上轉換 ； 低折射率

並列摘要

The enhanced upconversion luminescence of lanthanide-ion(Ln3+) doped upconversion nanoparticles (UCNPs) is particularly important and highly required for their innumerable applications in fluorescence microscope, bio-imaging, sensing, solid-state lasers, 3D displays, and solar cells.In this study, we investigate the enhancement effect of upconversion fluorescence emission of UNCP by using low refractive index resonant waveguide grating(RWG) when both excitation and extraction resonance occur in the waveguide structure.The method to fabricate one-dimensional grating patterns with nanoporous SiO2, a low refractive index material (n=1.22), using nanoimprint lithography is reported. A guided mode resonant structure is obtained by subsequent sputtering of thin film of high refractive index titanium dioxide (TiO2) on the sample surface, and then NaYF4:Yb3+,Tm3+ nanoparticles are deposited onto the top cladding layer of a RWG structure by dip-coating method.We demonstrate the up-conversion photoluminescence signal generated from the rare-earth nanocrystal coated on top of such RWG structure can be enhanced up to 10^4 times when both excitation and extraction resonance are simultaneously achieved, compared with UCNPs on an non-patterned surface.
Keywords : Low-refractive index , Up conversion, Rare earth, Fluorescence, Guided-mode resonance

並列關鍵字

Guided-mode resonance ； Fluorescence ； Rare earth ； Up conversion ； Low-refractive index

參考文獻

[1] Yablonovitch, E. Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review Letters 1987, 58 (20), 2059.

[2] John, S. Strong Localization of Photons in Certain Disordered Dielectric Superlattices. Physical Review Letters 1987, 58 (23), 2486.

[3] Krauss, T. F.; Brand, S. Two-Dimensional Photonic-BandGap Structures Operating at near-Infrared Wavelengths. Nature 1996, 383 (6602), 699–702.

[4] Lin, J. H.; Liou, H. Y.; Wang, C.-D.; Tseng, C.-Y.; Lee, C.-T.; Ting, C.-C.; Kan, H.-C.; Hsu, C. C. Giant Enhancement of Upconversion Fluorescence of NaYF4: Yb3+ ,Tm3+ Nanocrystals with Resonant Waveguide Grating Substrate. ACS Photonics 2015, 2 (4), 530–536.

[5] Heer, S.; Kömpe, K.; Güdel, H.-U.; Haase, M. Highly Efficient Multicolour Upconversion Emission in Transparent Colloids of Lanthanide-Doped NaYF4 Nanocrystals. Advanced Materials 2004, 16 (23-24), 2102–2105.