Hole Surface Trapping Dynamics Directly Monitored by Electron Spin Manipulation in CdS Nanocrystals.
A new detection technique, pump-spin orientation-probe ultrafast spectroscopy, is developed to study the hole trapping dynamics in colloidal CdS nanocrystals. The hole surface trapping process spatially separates the electron-hole pairs excited by the pump pulse, leaves the core negatively charged, and thus enhances the electron spin signal generated by the orientation pulse. The spin enhancement transients as a function of the pump-orientation delay reveal a fast and a slow hole trapping process with respective time constants of sub-10 ps and sub-100 ps, orders of magnitude faster than that of carrier recombination. The power dependence of hole trapping dynamics elucidates the saturation process and relative number of traps, and suggests that there are three subpopulations of nanoparticles related to hole surface trapping, one with the fast trapping pathway only, another with the slow trapping pathway only, and the third with both pathways together.
†State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Xiao
X
Li
†State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Donghai
D
Feng
†State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Haifang
H
Tong
†State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Tianqing
T
Jia
†State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Li
L
Deng
†State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China.
Zhenrong
Z
Sun
‡State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.
Zhizhan
Z
Xu
charge carrier trapping; colloidal nanocrystals; pump−probe; spin dynamics; ultrafast transient spectroscopy