Solution control of radiative and nonradiative lifetimes: a novel contribution to quantum dot blinking suppression.

Time-correlated single photon counting methods are used with confocal microscopy and maximum likelihood estimation analysis to obtain fluorescence lifetime trajectories for single quantum dots with KHz update rates. This technique reveals that control of the solution environment can influence both radiative (k(rad)) and nonradiative (k(nonrad)) pathways for electron-hole recombination emission in a single quantum dot and provides a novel contribution mechanism to nearly complete suppression of quantum dot blinking, specifically by an increase in k(rad*).

Ultrafast hot-carrier dynamics at chemically modified Ge interfaces probed by SHG.

Time-resolved second-harmonic generation (SHG) was used to study the hot-carrier dynamics and nonlinear optical properties of S-terminated and Cl-terminated Ge(111) interfaces on the femtosecond time scale. The hot-carrier second-order nonlinear optical susceptibilities were determined to be 720 +/- 50 times greater than the valence-band second-order nonlinear optical susceptibilities for the Ge(111)-S system and 880 +/- 100 times greater in the Ge(111)-Cl system. Furthermore, the ground- and excited-state second-order nonlinear optical susceptibilities are suggested to be out of phase for Ge(111)-S and Ge(111)-Cl systems, leading to a pump-induced decrease in the SHG signal as opposed to the increase in the SHG signal observed in the Ge(111)-GeO2 system. Although the SHG response reaches a steady state in 415 +/- 90 fs in the Ge(111)-GeO2 system, a faster response is observed in the Ge(111)-S system, 220 +/- 85 fs, and in the Ge(111)-Cl system, 172 +/- 50 fs. This suggests significantly faster carrier cooling at the Ge(111)-Cl and Ge(111)-S interfaces, with significant implications for hot-carrier mediated device degradation, and migration to high-K dielectrics.