Hiroyuki Sakamoto

Oxidative aromatic ring cleavage of 3,5-di-t-butylcatechol, with total insertion of molecular oxygen, catalysed by 2,2′-bipyridine–iron(II) complex

The oxidative aromatic ring cleavage of 3,5-di-t-butylcatechol (1) by molecular oxygen to give the lactone (2) is catalysed by a non-enzymatic iron(II) complex co-ordinated by 2,2′-bipyridine and pyridine.

Directional outcoupling of photoluminescence from Eu(III)-complex thin films by plasmonic array

A plasmonic array, consisting of metallic nanocylinders periodically arranged with a pitch comparable to the optical wavelength, is a system in which both the localized surface plasmon polaritons (SPPs) and diffraction in the plane of the array are simultaneously excitable. When combined with a phosphor film, the array acts as a photoluminescence (PL) director and enhancer. Since the array can modify both excitation and emission processes, the overall modification mechanism is generally complex and difficult to understand. Here, we examined the mechanism by simplifying the discussion using an emitter with a high quantum yield, large Stokes shift, and long PL lifetime. Directional PL enhancement as large as five-fold occurred, which is mainly caused by outcoupling, i.e., the PL trapped in the emitter film by total internal reflection is extracted into free space through the SPPs and diffraction. The present scheme is robust and applicable to arbitrary emitters, and it is useful for designing compact and ef...

Mesoporous silica layer on plasmonic array: light trapping in a layer with a variable index of refraction

Mesoporous silica layers with open and accessible mesopores were fabricated on aluminum nanoparticle arrays. The system can support plasmonic-photonic hybrid modes that are radiatively coupled surface plasmon polaritons in the nanoparticles. The coupling is mediated either by diffraction in the plane of the array or by waveguiding in the dielectric silica layer covering the array. Upon irradiation of an array with visible light, these hybrid modes are excited and appear as sharp spectral dips in optical transmission, a manifestation of light trapping in the system. The porous nature of the layers can be taken advantage of, via pore infiltration, to facilitate control over the layer’s refractive index. We demonstrated tuning in the wavelength and spatial distribution of trapped light in the system.

Excitation of collective plasmonic modes and photoluminescence enhancement in the Al nanocylinder array

Periodic arrays of metallic nanocylinder combined with the luminous layer are the good platform to control the properties of photoluminescence (PL). The array structure is especially useful to directionally enhance PL from the emitters of high quantum yield, in sharp contrast to a vast majority of the plasmonic nanostructures which decrease the PL intensity from such good emitters. The trick is to use collective plasmonic mode, i.e., the radiative coupling of surface plasmon polaritons via the in-plane diffraction. In this study, we demonstrated the directional PL enhancement using the high quantum yield emitters such as Eu(III)-complex and rhodamine 6G on the periodic array of Al nanocylinders. The result is useful for designing the compact and efficient luminescence source with directional output.