Ultrafast carrier dynamics in semiconductor quantum dots

Excitonic nonlinear absorption in CdS nanocrystals studied using Z-scan technique

“…25,26 Apparently, the value of Imχ (3) QD is significantly increased as the investigated wavelength approaching the exciton peak. Although the α 2 values are similar for the two samples, the intrinsic Imχ (3) QD is greatly enhanced for the smaller CdS particle size by taking consideration of the different volume fraction in the two samples.…”

“…22 By considering the population redistribution under the laser radiation of frequency ω, the susceptibility, χ = Reχ -i Imχ, can be derived as a function of |E 0 | 2 , where E 0 is the electric field strength of the laser light. To obtain the third-order and fifth-order nonlinear absorption, Imχ (3) and Imχ (5) can be expanded in terms of |E 0 | 2 and written down in the following: where µ is the dipole moment, T 2 the dephasing time, τ the relaxation time, ∆N 0 the population difference at zero field, ε 0 the permittivity in vacuum, ћ the Plank's constant, and ω 0 the exciton frequency. Up to date no accurate calculation can be found in literature for the dipole moment, µ = <Φ 1 |er|Φ 2 >, of CdS NCs.…”

“…[1][2][3][4][5][6][7][8][9] This interest is stimulated by remarkably different optical properties when semiconductor sizes are decreased from bulk to a few nanometers as predicted by quantum confinement theory.…”

“…[10][11][12][13][14] And the excited state dynamics have been studied in detail with femtosecond time-resolved pump-probe and photoluminescence (PL) technique. 3,15,16 Compared to DFWM and pump-probe technique, Z-scan is an effective technique to investigate nonlinear absorption and nonlinear refraction separately. Recently, there have been several reports on CdS nanoparticles studied by the use of Z-scan technique.…”

Optical nonlinearities and ultrafast carrier dynamics in semiconductor quantum dots

“…This can be explained in terms of confinement-induced squeezing of the 1S electron wave function, resulting in an increased overlap with the wave function of the deep-trap state. "Application of iii up-conversion photoluminescence and TA allowed us to separate electron and hole relaxation paths [8]. We observed very fast PL decay (attributed to sub-ps hole trapping).…”