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Kanemitsu Laboratory,
Institute for Chemical Research, Kyoto University, Uji, Kyoto, Japan


Kyoto University

Institute for Chemical Research

Faculty of Science

Division of Physics and Astronomy

Scope of Research

Our research interest is to understand optical and quantum properties of nanometer-scale materials and to develop opto-nanoscience for creation of innovative functional materials. Optical responses of semiconductor quantum nanostructures and low-dimensional strongly correlated electron systems are studied by means of space- and time-resolved laser spectroscopy.

The main subjects are as follows:
  1. Development of high-resolution scanning near-field optical microscope and optical properties of single nanostructures.
  2. Ultrafast optical spectroscopy of excited states of semiconductor nanostructures.
  3. Development of nanoparticles with new optical functions.


Single Nanoparticle Spectroscopy
Semiconductor nanoparticles of sizes comparable to or smaller than the exciton Bohr radius in bulk materials have attracted much attention, because they exhibit a wealth of quantum phenomena. We have prepared semiconductor nanoparticles embedded in dielectric matrices by many different techniques and discussed luminescence properties of single semiconductor nanoparticles studied by selective excitation spectroscopy and scanning near-field optical microscopy at low temperatures. The free-exciton and shallow-impurity luminescence show very narrow line widths. The deep impurity luminescence is broad even in single nanoparticles. We discussed the mechanism of the exciton-phonon coupling in semiconductor nanoparticles.
Femtosecond Laser Spectroscopy of Wide Band-Gap Semiconductors
Recently, there has been great interest in the optical processes in wide-gap semiconductors. The developments of wavelength-tunable femtosecond laser systems and remarkable progress in semiconductor crystal growth have enabled us to study intrinsic optical processes and dynamics. Because of the large exciton binding energy, GaN and related materials provide us an excellent stage for the study of the excitonic many-body effects in semiconductors. We have clarified the luminescence processes in highly excited GaN and InGaN semiconductors by means of optical Kerr-gate time-resolved photoluminescence measurements.
Optical near-field spectroscopy of semiconductor quantum structures
Near-field scanning optical microscope with a spatial resolution of 100-150 nm (l/7-l/5, l: wavelength of light) has contributed to explorer novel electronic and optical properties of semiconductor quantum structures. Recently, the spatial resolution as high as 30 nm (l/30) has been achieved employing a specially designed fiber probe with a small and clear aperture in photoluminescence measurements of the semiconductor quantum structures. With using this advanced tool, we have demonstrated that the local optical probe directly maps out the center-of-mass wave function of an exciton confined in a GaAs quantum dot by the high-resolution photoluminescence image. The photoluminescence image in a biexciton (bounded two-excitons due to Coulomb interactions) state differs from that in an exciton state due to different distributions of the polarization field for the exciton and biexciton recombinations.