National Institute for Materials Science (NIMS) , 1-1 Namiki, Tsukuba 305-0044, Japan.
Graduate School of Pure and Applied Sciences, Tsukuba University , 1-1-1 Tennodai, Tsukuba 305-8571, Japan.
Nano Lett. 2016 Aug 10;16(8):5191-6. doi: 10.1021/acs.nanolett.6b02200. Epub 2016 Jul 20.
Lanthanoid series are unique in atomic elements. One reason is because they have 4f electronic states forbidding electric-dipole (ED) transitions in vacuum and another reason is because they are very useful in current-day optical technologies such as lasers and fiber-based telecommunications. Trivalent Er ions are well-known as a key atomic element supporting 1.5 μm band optical technologies and also as complex photoluminescence (PL) band deeply mixing ED and magnetic-dipole (MD) transitions. Here we show large and selective enhancement of ED and MD radiations up to 83- and 26-fold for a reference bulk state, respectively, in experiments employing plasmonic nanocavity arrays. We achieved the marked PL enhancement by use of an optimal design for electromagnetic (EM) local density of states (LDOS) and by Er-ion doping in deep subwavelength precision. We moreover clarify the quantitative contribution of ED and MD radiations to the PL band, and the magnetic Purcell effect in the PL-decay temporal measurement. This study experimentally demonstrates a new scheme of EM-LDOS engineering in plasmon-enhanced photonics, which will be a key technique to develop loss-compensated and active plasmonic devices.
镧系元素在原子元素中是独特的。原因之一是它们具有 4f 电子态，在真空中禁止电偶极（ED）跃迁；另一个原因是它们在当前的光学技术中非常有用，如激光和光纤通信。三价铒离子是支持 1.5μm 波段光学技术的关键原子元素，也是复杂光致发光（PL）带深混合 ED 和磁偶极（MD）跃迁的关键原子元素。在这里，我们通过等离子体纳米腔阵列实验表明，在参考体状态下，ED 和 MD 辐射分别实现了高达 83 倍和 26 倍的大选择性增强。我们通过对电磁场（EM）局域态密度（LDOS）进行最佳设计，并在深亚波长精度下进行 Er 离子掺杂，实现了显著的 PL 增强。我们还澄清了 ED 和 MD 辐射对 PL 带的定量贡献，以及在 PL 衰减时间测量中的磁普塞尔效应。本研究通过实验证明了等离子体增强光子学中 EM-LDOS 工程的新方案，这将是开发损耗补偿和有源等离子体器件的关键技术。
