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We investigated vibrational energy relaxations of S 1 perylene at an excess energy of ca. 2800 cm -1 in several ketone solvents by femtosecond time-resolved fluorescence measurements.Temporal evolution of fluorescence emissions occurs on the following distinct timescales: 70 ~ 330 fs, 0.6 ~ 1.1 ps and 1.8 ~ 4.9 ps. The latter two was assigned to the intramolecular vibrational redistribution (IVR), and to the solvent-assisted IVR (SA-IVR), respectively. In SA-IVR, intramolecular vibrational couplings are affected by elastic or quasi-elastic interactions between solute and solvents. Solvent dependence of the SA-IVR rates can be explained qualitatively by the tier V-V coupling mechanism.

We successfully fabricated defect-free, distributed and sub-20-nm GaAs quantum dots (named GaAs nanodisks (NDs)) by using a novel top-down technique that combines a new bio-template (PEGylated ferritin) and defect-free neutral beam etching (NBE). Greater flexibility was achieved when engineering the quantum levels of ND structures resulted in greater flexibility than that for a conventional quantum dot structure because structures enabled independent control of thickness and diameter parameters. The ND height was controlled by adjusting the deposition thickness, while the ND diameter was controlled by adjusting the hydrogen-radical treatment conditions prior to NBE. Photoluminescence emission due to carrier recombination between the ground states of GaAs NDs was observed, which showed that the emission energy shift depended on the ND diameters. Quantum level engineering due to both diameter and thickness was verified from the good agreement between the PL emission energy and the calculated quantum confinement energy.

Articles you may be interested inThe growth-temperature dependence of the optical spin-injection dynamics in self-assembled quantum dots (QDs) of In 0.5 Ga 0.5 As was studied by increasing the sheet density of the dots from 2 Â 10 10 to 7 Â 10 10 cm À2 and reducing their size through a decrease in growth temperature from 500 to 470 C. The circularly polarized transient photoluminescence (PL) of the resulting QD ensembles was analyzed after optical excitation of spin-polarized carriers in GaAs barriers by using rate equations that take into account spin-injection dynamics such as spin-injection time, spin relaxation during injection, spin-dependent state-filling, and subsequent spin relaxation. The excitation-power dependence of the transient circular polarization of PL in the QDs, which is sensitive to the state-filling effect, was also examined. It was found that a systematic increase occurs in the degree of circular polarization of PL with decreasing growth temperature, which reflects the transient polarization of exciton spin after spin injection. This is attributed to strong suppression of the filling effect for the majority-spin states as the dot-density of the QDs increases.

We have demonstrated the fabrication of homogeneously distributed In 0.3 Ga 0.7 N/GaN quantum nanodisks (QNDs) with a high density and average diameter of 10 nm or less in 30-nm-high nanopillars. The scalable top-down nanofabrication process used biotemplates that were spincoated on an In 0.3 Ga 0.7 N/GaN single quantum well (SQW) followed by low-damage dry etching on ferritins with 7 nm diameter iron cores. The photoluminescence measurements at 70 K showed a blue shift of quantum energy of 420 meV from the In 0.3 Ga 0.7 N/GaN SQW to the QND. The internal quantum efficiency of the In 0.3 Ga 0.7 N/GaN QND was 100 times that of the SQW. A significant reduction in the quantum-confined Stark effect in the QND structure was observed, which concurred with the numerical simulation using a 3D Schrodinger equation. These results pave the way for the fabrication of large-scale III− N quantum devices using nanoprocessing, which is vital for optoelectronic communication devices.