Long-Lived Population Inversion in Isovalently Doped Quantum Dots

Optical gain from colloidal quantum dots has been desired for several decades since their discovery. While gain from multiexcitations is by now well-established, nonradiative Auger recombination limits the lifetime of such population inversion in quantum dots. CdSe cores isovalently doped by one to few Te atoms capped with rod-shaped CdS are examined as a candidate system for enhanced stimulated emission properties. Emission depletion spectroscopy shows a behavior characteristic of 3-level gain systems in these quantum dots. This implies complete removal of the 2-fold degeneracy of the lowest energy electronic excitation due to the large repulsive exciton–exciton interaction in the doubly excited state. Using emission depletion measurements of the trap-associated emission from poorly passivated CdS quantum dots, we show that 3-level characteristics are typical of emission resulting from a band edge to trap state transition, but reveal subtle differences between the two systems. These results allow for unprecedented observation of long-lived population inversion from singly excited quantum dots

Enhanced Third-Harmonic Generation from a Metal/Semiconductor Core/Shell Hybrid Nanostructure

Nonlinear optical processes can be dramatically enhanced <i>via</i> the use of localized surface plasmon modes in metal nanoparticles. Here we show how more elaborate structures, based on shape-controlled Au/Cu₂O core/shell nanostructures, enable further enhancement of the nanoparticle third-harmonic scattering cross-section. The semiconducting component takes a twofold role in this structure, both providing a knob to tune the resonant frequency of the gold plasmon and providing resonant enhancement by virtue of its excitonic states. The advantages and deficiencies of using such core/shell metal/semiconductor structures are discussed

Characterizing the Quantum Confined Stark Effect in Semiconductor Quantum Dots and Nanorods for Single-Molecule Electrophysiology

We optimized the performance of quantum confined Stark effect QCSE based voltage nanosensors. A high throughput approach for single particle QCSE characterization was developed and utilized to screen a library of such nanosensors. Type II ZnSe CdS seeded nanorods were found to have the best performance among the different nanosensors evaluated in this work. The degree of correlation between intensity changes and spectral changes of the excitons emission under applied field was characterized. An upper limit for the temporal response of individual ZnSe CdS nanorods to voltage modulation was characterized by high throughput, high temporal resolution intensity measurements using a novel photon counting camera. The measured 3.5 us response time is limited by the voltage modulation electronics and represents about 30 times higher bandwidth than needed for recording an action potential in a neuron