Yoshihiko Kanemitsu

We report strong visible photoluminescence (PL) at room temperature from oxidized Si nanometer-sized spheres with a spherical crystalline Si (c-Si) core and an amorphous ${\mathrm{SiO}}_{2}$ (a-${\mathrm{SiO}}_{2}$) surface layer. The peak energy of the broad PL spectrum is about 1.65 eV, which is independent of the core diameter. We propose a model in which excitons are confined on a spherical shell, an interfacial layer between the c-Si core and the a-${\mathrm{SiO}}_{2}$ surface layer, and in

We have studied the microstructure and optical properties of free-standing porous Si thin films fabricated by electrochemical anodization. Raman-spectroscopy and transmission-electron-microscopy examinations show that Si crystallite spheres with diameters of several nanometers are dispersed in the amorphous phase. The blueshift of the optical-absorption spectrum is observed for decreasing average diameter of the Si crystallites. However, there is no clear size dependence of the peak energy of th

We have studied the origin of visible photoluminescence of Ge nanocrystals in SiO2 glassy matrix. Spectroscopic analyses of Ge nanocrystals indicate that the room-temperature photoluminescence comes from Ge nanocrystals of diameter of 4 nm or less. High-resolution electron microscopic studies imply that the structure of Ge nanocrystals of diameter ≤4 nm differs from the diamond structure. These data suggest that new nanostructure crystalline Ge having a character of direct optical transition exh

We have studied the mechanism of visible photoluminescence (PL) from surface-oxidized Si crystallites of 3.7 nm diameter. Under intense laser-pulse illumination, two PL bands are clearly observed: a fast-decay blue-green PL band and a slow-decay red PL band. Time-resolved PL-spectrum measurements indicate that carriers generated in the core state are rapidly localized into the lower-energy surface states. Spectroscopic analysis indicates that the slow-decay red PL is caused by the hopping-limite

All inorganic CsPbBr₃ perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot-injection method to partially replace the toxic Pb²⁺ with highly stable Sn⁴⁺ . Meanwhile, the absolute photoluminescence quantum yield of CsPb_1-x Sn_x Br₃ increased from 45 % to 83 % with Sn^IV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr₃ a

We have studied photoluminescence (PL) properties of surface-oxidized Si nanocrystals fabricated with a ${\mathrm{SiH}}_{4}$ plasma cell. The size dependence of the PL spectrum, the PL decay dynamics, and site-selective excitation spectroscopy show that the efficient and broad PL band around \ensuremath{\sim}1.65 eV originates from excitons localized at the interface between crystalline Si and the ${\mathrm{SiO}}_{2}$ surface layer. The PL from the crystalline Si core state in large nanocrystals

Abstract Strong electron-phonon interactions are frequently considered the origin of the unique electrical and optical properties of lead halide perovskites. Electron-phonon interactions induce the formation of a polaron, which is a charge carrier dressed with a phonon cloud. The details of polaron formation are crucial for carrier transport since polaron formation leads to a larger effective mass of a carrier. Several mechanisms have been proposed regarding the physics of polaron formation in h

This review summarizes the optical properties of lead-halide-perovskite thin films, single crystals, and solar-cell devices.

The lead halide perovskite semiconductor CH3NH3PbBr3 exhibits an intriguing difference between one-photon and two-photon excited photoluminescence spectra and dynamics. It is revealed that the dynamical photoluminescence behaviors are dominated by diffusion of photo­carriers from the near-surface region to the interior region of the single-crystal sample, due to the high mobilities of photoexcited electrons and holes.

We have studied the origin of the visible photoluminescence (PL) from oxidized porous Si fabricated by rapid-thermal-oxidization processes. At low oxidation temperature (${\mathit{T}}_{\mathrm{ox}}$), the PL spectrum with a peak near 750 nm is observed, and silicon oxyhydrides and silicon oxides are formed at the surface of nanocrystallites. At high ${\mathit{T}}_{\mathrm{ox}}$ above 800 \ifmmode^\circ\else\textdegree\fi{}C, strong blue PL is observed around 400 nm and the surface of crystallite

We have studied luminescence properties of nanometer-sized Si crystallites fabricated by laser breakdown of ${\mathrm{SiH}}_{4}$ gas. An exponential absorption tail is observed and red photoluminescence (PL) appears in the exponential tail. The PL decay behavior is characterized by a stretched exponential function. At higher temperatures, the effective PL decay rate ${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}1}$ depends exponentially on the monitored phonon energy \ensuremath{\Elzxh}\

We have studied optical properties of one-dimensional oligothiophenes and thiophene-based oligomers. The thiophene-based oligomers have the well-barrier-well structures in quasi-one-dimensional backbone chains, where the well parts are the oligothiophenes with different conjugation lengths and the barrier parts are nonvisibly luminescent materials with larger energy gaps. The chain-length dependence of the optical properties of oligothiophenes shows that excitons are localized within two thiophe

Combining the superior optical properties of their bulk counterparts with quantum confinement effects, lead halide perovskite nanocrystals are unique laser materials with low-threshold optical gain. In such nonlinear optical regimes, multiple excitons are generated in the nanocrystals and strongly affect the optical gain through many-body interactions. Here, we investigate the exciton-exciton interactions in CsPbI₃ nanocrystals by femtosecond transient absorption spectroscopy. From th