Effect of Cylinder Height on Directional Photoluminescence from Highly Luminous Thin Films on Periodic Plasmonic Arrays
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Effect of Cylinder Height on Directional Photoluminescence from Highly Luminous Thin Films on Periodic Plasmonic Arrays Motoharu Saito1, Shunsuke Murai1,2, Hiroyuki Sakamoto1, Masanori Yamamoto3, Ryosuke Kamakura1, Takayuki Nakanishi3, Koji Fujita1, Yasuchika Hasegawa3, and Katsuhisa Tanaka1 1
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto, 606-8510, Japan 2 PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan 3 Faculty of Engineering, Hokkaido University, North-13 West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan ABSTRACT Periodic array of metallic nanocylinder combined with the highly luminous dielectric layer is a good platform to control the intensity, spectral shape and directionality of photoluminescence (PL). In spite of its importance, the effect of cylinder height on the PL properties has not been verified experimentally. Here we investigate the effect of cylinder height on the PL properties both experimentally and numerically. The system consisted of a highly luminous layer made of Eu(III) complex and a series of periodic array of aluminum nanocylinders with different heights. The strongest directional PL was achieved when the height is similar to the diameter, i.e., the aspect ratio close to unity. Our finding is useful for designing the compact and efficient luminescence source with directional output. INTRODUCTION Photoluminescence (PL) control by coupling optical emitter with metallic structures has been studied since the demonstration of PL lifetime modulation by the presence of metallic flat surface near an optical emitter [1]. Since then, a variety of nanostructures has been proven useful to control PL, such as single [2, 3] or pair of nanoparticles [4–6], one- and two-dimensional gratings [7–9], and optical Yagi-Uda antenna [10]. We focus on periodic array, where metallic nanocylinders are arranged periodically with the pitch comparable to the optical wavelength [11, 12]. In such a structure, both light diffraction and surface plasmon polaritons (SPPs) can be excited upon light irradiation. Under certain conditions, light diffraction in the plane of the array can mediate the radiative coupling between the SPPs in neighboring nanocylinders. Consequently the SPPs in each nanocylinder oscillate in phase to provide a collective plasmonic mode, which is stronger in intensity than the simple sum of each SPP. When an emitter layer is deposited on the periodic array, the PL from the emitter is modified drastically. Compared to the other metallic nanostructures, the periodic array works more efficient in enhancing the PL of emitters with very high quantum yield [13–17]. Thus the combination of periodic arrays with luminous thin films is useful for obtaining compact and directional light sources. We can shape the PL by designing the array. The periodicity of the array dominates the directionality, since it determines the condition of light diffraction. The choice of metal is also important to sustain SPPs in t
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