We have studied a two-photon absorption (TPA) process and luminescent properties of biexcitons in CuCl quantum dot (QD) ensembles. The CuCl QDs embedded in NaCl single crystals were produced by means of the transverse Bridgman method and succeeding heat treatment. The resonant TPA band of the biexcitons was observed clearly in the photoluminescence (PL) excitation spectrum because of the large biexciton binding energy. We clarified that size selective excitation of the biexcitons is possible under the resonant TPA process. On the other hand, under the strong excitation, the PL of the biexcitons exhibited a transition from a spontaneous emission to a superfluorescence, a cooperative emission from coherently coupled excited two-level systems, with an increase in the excitation density. In addition, the ultrafast superfluorescent pulsed emission appeared using a short pulse laser system. Our results showed a capacity to control luminescent dynamics and coherent coupling of semiconductor QDs by an optical excitation process. In addition, a possibility of generating ultrashort pulsed superfluorescence was suggested for semiconductor QDs.
In this study, we investigated the geometric and electronic structures of the products obtained by reacting [Au25(SC2H4Ph)18]− with PhSeH or (PhTe)2 by single-crystal X-ray structural analysis, differential pulse voltammetry, and optical absorption spectroscopy. The results revealed that these exchange reactions preferentially produce products containing substituted ligands close to the gold core. In addition, we quantitatively determined the changes in the redox potentials and optical transition energies induced by continuous ligand exchange. This systematic investigation revealed that exchange with SePh induces nonlinear changes in the electronic structure of the clusters with the number of exchanged ligands. These findings are expected to lead to the improved designguidelines to produce clusters with new functions by ligand exchange with other chalcogenates.
It is well known that the strong electromagnetic field is generated at the metal nanostructure surface due to the excitation of collective oscillation of the conduction electrons, which is called localized surface plasmon (LSP). The near-field which is excited by LSP can be applied for many various nanophotonic technologies, such as biological sensors, surface enhanced Raman scattering, and photovoltaic devices. Especially for the case of the nano-dimer structures, the enhanced near-field is generated at the gap of nano-dimer and its strength strongly depends on the metal species, the shape or the gap distance. Although there are many well established top-down methods for the fabrication of the metal nanostructures, it is still difficult to control the structures in an atomic scale precisely. In this study, we have tried to establish novel approach for the precision control of the gap distance and the shape of Au nano-dimer structures in a single nanometer scales using electrochemical method. In order to make a detailed assessment of the optical properties changes, in-situ extinction measurements were performed during electrochemical measurements.
In this study, applying to touch sensor, metal mesh based on copper (Cu) was fabricated on a glass substrate with thin film fabrication of Cu followed by photo-lithography. Firstly, conditions to optimize electrical properties of Cu thin film was investigated. Cu thin film was fabricated with sputtering method while controlling grain size with thickness of the thin film. As a result, by establishing sputtering parameters, an optimized Cu thin film was achieved with electrical sheet resistance and resistivity of 0.0757 Ω/sq. and 2.5854 μΩ・cm. In addition, adhesion of the Cu thin film was favorable. Then, fine line of Cu mesh was fabricated by optimizing photo-lithography conditions. High optical transmittance and low reflectance of the Cu mesh were achieved as 88.8% and 8.0% under air reference, respectively.