Piątkowski Dawid, Schmidt Mikołaj K, Twardowska Magdalena, Nyk Marcin, Aizpurua Javier, Maćkowski Sebastian
Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
Centro de Física de Materiales (MPC, CSIC-UPV/EHU) and Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián, Spain.
Materials (Basel). 2017 Aug 4;10(8):905. doi: 10.3390/ma10080905.
We experimentally demonstrate strong spectral selectivity of plasmonic interaction that occurs between α-NaYF₄:Er/Yb nanocrystals, which feature two emission bands, and spherical gold nanoparticles, with plasmon frequency resonant with one of the emission bands. Spatially-resolved luminescence intensity maps acquired for individual nanocrystals, together with microsecond luminescence lifetime images, show two qualitatively different effects that result from the coupling between plasmon excitations in metallic nanoparticles and emitting states of the nanocrystals. On the one hand, we observe nanocrystals, whose emission intensity is strongly enhanced for both resonant and non-resonant bands with respect to the plasmon resonance. Importantly, this increase is accompanied with shortening of luminescence decays times. In contrast, a significant number of nanocrystals exhibits almost complete quenching of the emission resonant with the plasmon resonance of gold nanoparticles. Theoretical analysis indicates that such an effect can occur for emitters placed at distances of about 5 nm from gold nanoparticles. While under these conditions, both transitions experience significant increases of the radiative emission rates due to the Purcell effect, the non-radiative energy transfer between resonant bands results in strong quenching, which in that situation nullifies the enhancement.
我们通过实验证明了α-NaYF₄:Er/Yb纳米晶体（具有两个发射带）与球形金纳米颗粒之间发生的等离子体相互作用具有很强的光谱选择性，其中金纳米颗粒的等离子体频率与其中一个发射带共振。为单个纳米晶体获取的空间分辨发光强度图，以及微秒级发光寿命图像，显示了金属纳米颗粒中的等离子体激发与纳米晶体的发射态之间的耦合产生的两种性质不同的效应。一方面，我们观察到纳米晶体，其对于与等离子体共振相关的共振和非共振带的发射强度都有强烈增强。重要的是，这种增强伴随着发光衰减时间的缩短。相比之下，大量纳米晶体表现出与金纳米颗粒的等离子体共振共振的发射几乎完全淬灭。理论分析表明，对于距离金纳米颗粒约5 nm处的发射体，可能会出现这种效应。在这些条件下，由于珀塞尔效应，两个跃迁的辐射发射率都会显著增加，但共振带之间的非辐射能量转移会导致强烈淬灭，在这种情况下会抵消增强效果。
