Coupled Exciton and Charge-Transfer Resonances in the Raman Enhancement of Phonon Modes of CdSe Quantum Dots (QDs)

• NCJ Number: 304221
• Journal: Journal of Physical Chemistry C Volume: 118 Issue: 33 Dated: 2014 Pages: 19415–19421
• Author(s): Syed K. Islam; Mohammad A. Sohel; John R. Lombardi
• Date Published: 2014
• Length: 7 pages
• Grant Number(s): 2009-DN-BX-K185
• Agencies: NIJ-Sponsored
• Award: Development Of Advanced Raman Spectroscopy Methods And Databases For The Evaluation Of Trace Evidence And The Examination Of Questioned Documents-Phase II

Annotation

This article reports on a project that observed the enhancement of a transverse optical (TO) phonon mode of e1 symmetry and a normally forbidden surface optical (SO) phonon mode of b1 symmetry in CdSe quantum dots (QDs) due to adsorption of 4-mercaptopyridine molecules.

Abstract

The former was observed in 3, 4, and 5 nm diameter particles, while the latter was observed only in the 2 nm particles. Maximum enhancement of the phonon modes was obtained through a coupling of the charge-transfer transition and the exciton transition, which are in resonance with the laser energy. Selection rules, using Herzberg–Teller (vibronic) coupling, were invoked to explain the observed enhancements. (publisher abstract modified)