Enhanced and Polarized Photoluminescence from Carbon Dot–Metal Nanoparticle Composites

Carbon dots are attracting much attention because of their low toxicity, biocompatibility, and photostability. In this study, we fabricate carbon dot–metal nanoparticle composites using electron-beam-induced chemical reactions to improve the photoluminescence characteristics. We investigate the spectral characteristics of the composites by linear and nonlinear optical spectroscopy. The composites show plasmon resonance depending on the material used. The linear and nonlinear photoluminescence from the composites are enhanced by plasmon excitations, and the enhancement reaches nearly several times and 20 times, respectively. We also fabricate nanowire structures containing the composites. The structures show very intense photoluminescence and unique polarization characteristics depending on the wire width. We reveal that the polarization characteristics originate from the plasmonic coupling along the short axis of the wire. The technique developed in this study is promising for the polarization control of light-emitting elements and the creation of new functional nanomaterials

Space-Selective Fabrication of Light-Emitting Carbon Dots in Polymer Films Using Electron-Beam-Induced Chemical Reactions

Nanocarbon-based materials have excellent properties, including high electrical conductivity as well as charity-dependent optical absorption and luminescence; therefore, the materials are promising in applications for nanoelectric devices, nanophotonics, and so on. Carbon dots (CDs) are one of the carbon materials recently fabricated. Optical properties of CDs have been reported to be similar to those of polycyclic aromatic hydrocarbons (PAHs). For this reason, the CDs are considered to be composed of PAH. Synthesis of CDs has previously been accomplished through hydrothermal synthesis and microwave irradiation. These methods require a long synthesis time, and the processes involve multiple steps. In this study, we developed a fabrication method of CDs in simple and spatially selective ways, by using radical reactions in an organic polymer film with focused electron-beam irradiation. We investigated various organic polymers as reaction materials and found that polystyrene has a higher efficiency for CD formation than other organic polymers investigated. Absorption, photoluminescence, and Raman scattering properties of the electron-beam-irradiated sample were in good agreement with those reported for the CDs. The technique developed in this study is promising for fabricating light-emitting CDs and photonic crystals in a simple and flexible manner