†Department Chemie and CeNS, Ludwig-Maximilians-Universität München, 81377 München, Germany.
‡Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
ACS Nano. 2015 Apr 28;9(4):3617-26. doi: 10.1021/nn504993e. Epub 2015 Mar 18.
We present tip-enhanced upconversion photoluminescence (PL) images of Er(3+)- and Yb(3+)-doped NaYF4 nanocrystals on glass substrates with subdiffraction spatial resolution. Tip-sample distance dependent measurements clearly demonstrate the near-field origin of the image contrast. Time-resolved PL measurements show that the tip increases the spontaneous emission rate of the two emission channels of Er(3+) in the visible region. Very efficient enhancement of upconversion PL is discussed in the context of the two-photon nature of the excitation process and homoenergy transfer between the ions within the nanocrystals. Comparison between different nanocrystals and tips shows a strong influence of the tip shape on the image contrast that becomes particularly relevant for the larger dimensions of the investigated nanocrystals.
我们展示了在玻璃衬底上的 Er(3+)和 Yb(3+)掺杂的 NaYF4 纳米晶体的 tips-enhanced 上转换光致发光（PL）图像，其空间分辨率达到了亚衍射极限。tip-sample 距离相关的测量清楚地证明了图像对比度的近场起源。时间分辨的 PL 测量表明，针尖增加了 Er(3+)在可见光区域的两个发射通道的自发发射速率。在激发过程的双光子性质和纳米晶体中离子之间的同能量转移的背景下，讨论了上转换 PL 的非常有效的增强。不同纳米晶体和 tips 之间的比较表明，针尖形状对图像对比度有强烈的影响，对于所研究的纳米晶体的较大尺寸，这种影响变得尤为重要。
