氮化鉿電漿子奈米結構共振增強二維鉛基鹵素鈣鈦礦的上轉換螢光

二維鈣鈦礦(Ruddlesden-Popper phase perovskite)，因為其自有的有機無機層形成材料自發的量子井，不只能夠提升材料的發光效率，無機層的存在更能作為鈣鈦礦的鈍化層，阻擋來自空氣中的水氣和氧氣，使得其在發光特性上比傳統鈣鈦礦來的更加優異。在本篇研究中，我們選用的混合陽離子準二維鈣鈦礦HA2(Cs0.5FA0.5)n-1PbnBr3n+1對其進行實驗。我們對準二維鈣鈦礦進行溫度變化螢光光譜，時間解析螢光光譜，瞬態吸收光譜的量測，了解其內部載子行為，進而發掘其基礎的光學特性。在瞬態吸收光譜中，我們發現準二維鈣鈦礦的載子，會在很短的時間(大約一皮秒)從能量較大的能階遷移至能量較低的能階，也就是從較小的n區域遷移至較大的n區域，形成了有助於雷射產生的四能階系統。並以準二維鈣鈦礦的橢偏儀數據進行結構模擬。我們使用有限時域差分法（Finite-difference time-domain, FDTD）設計奈米級的領結結構(Bowtie structure)，理解其電漿共振的基本特性，製造隙電漿子產生局域場強進而增強準二維鈣鈦礦發光，並使用過渡金屬氮化物(Transition metal nitride, TMNs)進行奈米製程。這些難熔電漿子材料具有良好的化學穩定特性，能夠確保在激發樣品發光的同時不會因為雷射的高功率而損壞。在量測上以不同的激發光源來量測準二維鈣鈦礦在結構上的發光特性，其中又以鈦藍寶石(Ti-sapphire)飛秒脈衝雷射的結果最為特別。在其引發的雙光子激發過程中，我們觀測到二氧化矽基板上準二維鈣鈦礦發光強度對於激發光強度的響應斜率為2.7，而奈米結構上的準二維鈣鈦礦發光有120倍的增強，並透過改變激發光的偏振方向來確認結構增強發光的真實行為與模擬的對應。我們相信準二維鈣鈦礦在較長波長光譜的低吸收率，能有效降低激發光造成的熱累積，並且穿過鈣鈦礦直接在結構上形成隙電漿子，隙電漿子的局域場強使結構對激發光的吸收增加，進而產生更強的螢光發光。而未來透過優化結構以及準二維鈣鈦礦的製程參數，我們希望能夠在這樣的系統中達成上轉換奈米雷射。

關鍵字

隙電漿子；準二維鈣鈦礦；過渡金屬氮化物；奈米領結結構；上轉換螢光

並列摘要

Two-dimensional (2D) halide Ruddlesden-Popper perovskite has attracted tremendous attention recently, not only because the organic ligand can generate quantum well to improve the emission efficiency but also can be a passivation layer to resist the moisture from the air. However, the upconversion properties in quasi-2D halide perovskite have seldom been examined. Here, we demonstrated a giant enhancement of upconversion luminescence in quasi-2D halide perovskite (HA2(Cs0.5FA0.5)n-1PbnBr3n+1) film integrated with plasmonic bowtie nanocavity. We performed the absorption and the pump-probe transient absorption measurement in quasi-2D perovskite to obtain the fundamental optical properties. We found out that the carrier inside the quasi-2D halide perovskite film transport very quickly (around 1 ps). It funnels from high energy level to low energy level which means that the carrier will transport from a lower n 2D area to a higher n 2D area. This form a four-level system. To enhance the photoluminescence, we use the Finite-difference time-domain method (FDTD) to design a plasmonic nanocavity. The designed Bowtie structure was fabricated based on an alternative plasmonic material (Hafnium nitride) by using the nanofabrication process. We use an 800 nm Ti-Sapphire pulsed laser as an excitation source, the measured light-light curve shows a slope of 2.7 in quasi-2D perovskite on SiO2 substrate under two-photon excitation. When the quasi-2D perovskite integrated with HfN gap plasmon bowtie nanocavities, there is a 120 times intensity of upconversion luminescence under the same excitation condition. Furthermore, we performed the pump polarization-dependent measurement to study the light–matter interaction in the quasi-2D perovskite with gap plasmon nanocavity. We believe that the low absorption at the long wavelength (NIR region) could dramatically reduce the heat accumulation effect in the 2D perovskite, which could reduce the system loss in order to reach lasing condition. Hence, our results will open the door to achieving a quasi-2D Perovskite upconversion nanolaser operated at room temperature.

並列關鍵字

gap plasmon ； quasi-2D perovskite ； transition metal nitride(TMNs) ； bowtie structure ； upconversion photoluminescence

參考文獻

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