Observation of charged excitons in hole-doped carbon nanotubes using photoluminescence and absorption spectroscopy

We report the first observation of trions (charged excitons), three-particle bound states consisting of one electron and two holes, in hole-doped carbon nanotubes at room temperature. When p-type dopants are added to carbon nanotube solutions, the photoluminescence and absorption peaks of the trions appear far below the E11 bright exciton peak, regardless of the dopant species. The unexpectedly large energy separation between the bright excitons and the trions is attributed to the strong electron-hole exchange interaction in carbon nanotubes

Raman study on the interlayer interactions and the band structure of bilayer graphene synthesized by alcohol chemical vapor deposition

We investigated the electronic band structure and interlayer interactions in graphene synthesized by alcohol-chemical vapor deposition (a-CVD) using microprobe Raman spectroscopy and tight-binding band-structure calculations. The number of graphene layers was determined from the spectrally integrated intensity ratios of the G phonon to 2D phonon peaks. We found that the value of the parameter determining interlayer interactions in a-CVD bilayer graphene was less than half that of exfoliated bilayer graphene. The weak interlayer interaction in a-CVD bilayer graphene was attributed to non-AB stacking order

Origin of low-energy photoluminescence peaks in single carbon nanotubes: K -momentum dark excitons and triplet dark excitons

We performed photoluminescence (PL) spectroscopy on single carbon nanotubes to investigate the satellite PL peaks, which are much lower in energy than the lowest (E11) bright exciton peak. From the temperature and tube-diameter dependences of the PL spectra, we clarified two origins of the low-energy PL peaks. The weak peak, lying about 130 meV below the E11 bright exciton state, is well explained by the phonon sideband of the K-momentum dark exciton states above the lowest-bright exciton state. In addition, a strong PL peak appears after pulsed-laser irradiation, and its peak energy depends strongly on the tube diameter. This PL peak comes from the triplet dark exciton states

Evidence for dark excitons in a single carbon nanotube due to the Aharonov-Bohm effect

We studied exciton structures and the Aharonov-Bohm effect in a single carbon nanotube using micro-photoluminescence (PL) spectroscopy under a magnetic field at low temperatures. A single sharp PL peak from the bright exciton state of a single carbon nanotube was observed under zero magnetic field, and the additional PL of dark exciton state appeared below the bright exciton peak under high magnetic fields. It was found that the split between the bright and dark exciton states is several millielectron volts at zero field. The tube diameter dependence of the splitting arises from the intervalley short-range Coulomb interaction

Mechanism of exciton dephasing in a single carbon nanotube studied by photoluminescence spectroscopy

We studied the temperature and chirality dependence of the photoluminescence (PL) linewidth of single carbon nanotubes to clarify the mechanism of exciton dephasing. The PL linewidth of a single carbon nanotube broadened linearly with increasing temperature, indicating that the linewidth and exciton dephasing are determined through exciton-phonon interactions. From the chirality dependence of the PL linewidth, we concluded that exciton dephasing is caused by both the longitudinal acoustic and twisting phonon modes

Symmetry-induced nonequilibrium distributions of bright and dark exciton states in single carbon nanotubes

We investigated the magnetic and temperature dependence of the bright and dark exciton luminescence spectra in single carbon nanotubes. We found that the phonon-induced exciton scattering rate from the bright to the dark state is only one order of magnitude larger than the dark exciton recombination rate below 10 K at zero magnetic field. Our results indicate that excitons are nonequilibriumly distributed between the bright and dark states due to the different parities of the wave functions and that Aharonov-Bohm flux enhances the phonon-induced exciton scattering between these two states. Our nonequilibrium exciton distribution model can also explain the nonzero photoluminescence intensity at very low temperatures

Diurnal expression of MRP4 in bone marrow cells underlies the dosing-time dependent changes in the oxaliplatin-induced myelotoxicity

Abstract The expression and function of some xenobiotic transporters varies according to the time of day, causing the dosing time-dependent changes in drug disposition and toxicity. Multidrug resistance-associated protein-4 (MRP4), an ATP­binding cassette (ABC) efflux transporter encoded by the Abcc4 gene, is highly expressed in bone marrow cells (BMCs) and protects them against xenobiotics, including chemotherapeutic drugs. In this study, we demonstrated that MRP4 was responsible for the extrusion of oxaliplatin (L-OHP), a platinum (Pt)-based chemotherapeutic drug, from BMCs of mice, and that the efflux transporter expression exhibited significant diurnal variation. Therefore, we investigated the relevance of the diurnal expression of MRP4 in BMCs for L-OHP-induced myelotoxicity in mice maintained under standardized light/dark cycle conditions. After intravenous injection of L-OHP, the Pt content in BMCs varied according to the injection time. Lower Pt accumulation in BMCs was detected in mice after injection of L-OHP at the mid-dark phase, during which the expression levels of MRP4 increased. Consistent with these observations, the myelotoxic effects of L-OHP were attenuated when mice were injected with L-OHP during the dark phase. This dosing schedule also alleviated the L-OHP-induced reduction of the peripheral white blood cell count. The present results suggest that the myelotoxicity of L-OHP is attenuated by optimizing the dosing schedule. Diurnal expression of MRP4 in BMCs is associated with the dosing time-dependent changes in L-OHP-induced myelotoxicity