The influence of surface passivation on electronic energy relaxation dynamics of CdSe and CdSe/CdS nanocrystals studied using visible and near infrared transient absorption spectroscopy

Nanoscale
Chongyue Yi, Kenneth L Knappenberger

Abstract

Charge carrier relaxation dynamics of electronically excited CdSe and CdSe/CdS core/shell nanocrystals (NCs) were studied using femtosecond time-resolved transient absorption spectroscopy, employing both visible and near-infrared (NIR) probe laser pulses. Following 400 nm excitation, the combination of visible and NIR laser probe pulses were used to determine the influence of surface passivation on electronic relaxation dynamics for nanocrystals overcoated with either organic ligands or inorganic semiconductors. In particular, low-energy NIR photons were used to isolate transient absorption signals due to either electron and hole intraband transitions. Four relaxation components were detected for CdSe NCs passivated by organic molecules: (1) picosecond hole relaxation; (2) electron deep trapping; (3) electron surface trapping; and (4) exciton radiative recombination. Based on TA data collected over a broad energy range, electron deep trapping at Se(2-) sites was suppressed for CdSe NCs passivated by inorganic (CdS) semiconducting materials. By comparing the time-dependent transient absorption data of a series of CdSe/CdS NCs with different shell thicknesses, evidence for the transition from Type-I to quasi Type-II NCs was obtai...Continue Reading

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Citations

Feb 13, 2016·Nanoscale·Aidi ZhangJicun Ren
Apr 16, 2019·Optics Letters·Megan A StevesKenneth L Knappenberger
Mar 23, 2019·The Journal of Physical Chemistry. a·Matthew N AshnerWilliam A Tisdale

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