Fast spontaneous emission and high F\"orster resonance energy transfer rate in hybrid organic/inorganic plasmonic nanostructures

We report an experimental study of the plasmon-assisted spontaneous emission and the F\"orster resonance energy transfer between organic molecules and semiconductor colloidal quantum dots. The localized plasmonic field in the nanogap between a gold nano-popcorn's tips and a 5-nm separated gold film supports high photonic density of states and provides pathways for the light-matter interaction mechanisms. We demonstrate that, besides the total spontaneous emission rate enhancement factor up to 66 for quantum dots and molecules, the F\"orster resonance energy transfer efficiency and rate constant are simultaneously modified. While the energy transfer efficiency is reduced from 84 to 35 per cent due to the non-radiative quenching effect and fast donor spontaneous emission rate, the energy transfer rate constant is significantly increased from 4 to 20 ns-1. Our results have quantitatively elucidated decay mechanisms that are important toward understanding and controlling of the light-matter interaction at the nanoscale.Comment: 12 pages, 4 Figures, Submitte

Temperature dependent dynamics of photoexcited carriers of Si2Te3 nanowires

We report an optical study of the dynamics of photoexcited carriers in Si2Te3 nanowires at various temperatures and excitation powers. Si2Te3 nanowires were synthesized, by using gold as a catalyst, on a silicon substrate by the chemical vapor deposition method. The photoluminescence spectrum of Si2Te3 nanowires was primary dominated by defect and surface states related emission at both low and room temperatures. We observed that the decay time of photoexcited carries was very long (> 10 ns) at low temperatures and became shorter (< 2 ns) at room temperature. Further, the carrier decay time became faster at high excitation rates. The acceleration of the photoexcited carrier decay rates indicate the thermal quenching along with the non-radiative recombination at high temperature and excitation power. Our results have quantitatively elucidated decay mechanisms that are important towards understanding and controlling of the electronic states in Si2Te3 nanostructures for optoelectronic applications.Comment: 12 pages, 4 figures, submitte

Ultrasensitive N-photon interferometric autocorrelator

We demonstrate a novel method to measure the Nth-order (N=1, 2, 3, 4) interferometric autocorrelation with high sensitivity and temporal resolution. It is based on the combination of linear absorption and nonlinear detection in a superconducting nanodetector, providing much higher efficiency than methods based on all-optical nonlinearities. Its temporal resolution is only limited by the quasi-particle energy relaxation time, which is directly measured to be in the 20 ps range for the NbN films used in this work. We present a general model of interferometric autocorrelation with these nonlinear detectors and discuss the comparison with other approaches and possible improvements

Enhanced spontaneous emission from quantum dots in short photonic crystal waveguides

We report a study of the quantum dot emission in short photonic crystal waveguides. We observe that the quantum dot photoluminescence intensity and decay rate are strongly enhanced when the emission energy is in resonance with Fabry-Perot cavity modes in the slow-light regime of the dispersion curve. The experimental results are in agreement with previous theoretical predictions and further supported by three-dimensional finite element simulation. Our results show that the combination of slow group velocity and Fabry-Perot cavity resonance provides an avenue to efficiently channel photons from quantum dots into waveguides for integrated quantum photonic applications.Comment: 12 pages, 4 figure

Low-Temperature Optical Characterization of Single CdS Nanowires

We use spatially resolved micro-PL imaging at low temperature to study optical properties of two sets of CdS nanowires grown using 20 nm and 50 nm catalysts. We find that low temperature PL of single nanowires is an ideal technique to gauge the quality of a given growth run, and moreover enables the collection of detailed spatial information on single wire electronic states.Comment: IEEE Nano 2006 Proceeding

A hierarchical architecture for increasing efficiency of large photovoltaic plants under non-homogeneous solar irradiation

Under non-homogeneous solar irradiation, photovoltaic (PV) panels receive different solar irradiance, resulting in a decrease in efficiency of the PV generation system. There are a few technical options to fix this issue that goes under the name of mismatch. One of these is the reconfiguration of the PV generation system, namely changing the connections of the PV panels from the initial configuration to the optimal one. Such technique has been widely considered for small systems, due to the excessive number of required switches. In this paper, the authors propose a new method for increasing the efficiency of large PV systems under non-homogeneous solar irradiation using Series-Parallel (SP) topology. In the first part of the paper, the authors propose a method containing two key points: a switching matrix to change the connection of PV panels based on SP topology and the proof that the SP-based reconfiguration method can increase the efficiency of the photovoltaic system up to 50%. In the second part, the authors propose the extension of the method proposed in the first part to improve the efficiency of large solar generation systems by means of a two-levels architecture to minimize the cost of fabrication of the switching matrix

Temperature dependent photoluminescence of single CdS nanowires

Temperature dependent photoluminescence (PL) is used to study the electronic properties of single CdS nanowires. At low temperatures, both near-band edge (NBE) photoluminescence (PL) and spatially-localized defect-related PL are observed in many nanowires. The intensity of the defect states is a sensitive tool to judge the character and structural uniformity of nanowires. As the temperature is raised, the defect states rapidly quench at varying rates leaving the NBE PL which dominates up to room temperature. All PL lines from nanowires follow closely the temperature-dependent band edge, similar to that observed in bulk CdS.Comment: 11 pages, 4 figure