Defect Mediated Energy Transfer from Semiconductor Nanocrystals to a Molecular Probe
Solid surfaces have defects such as vacancies, interstitial atoms, and impurity atoms that affect their chemical reactivity. For catalysis applications, it is important to understand how the location and nature of the surface site impact the catalytic rate. However, it is challenging to determine directly the location and chemical or physical nature of surface defect sites. Recently, Mulvaney and co-workers1 used a molecular-probe approach to “label” surface defect sites on semiconductor nanocrystals. Their approach is based on energy transfer from nanocrystal defect site “donors” to molecular probe acceptors. To achieve their approach, the authors chose an AlexaFluor cadaverine dye probe whose excitation spectrum overlapped with the semiconductor defect emission feature that has been assigned to oxygen vacancies. Steady-state photoluminescence (PL) studies showed a decrease of the donor defect emission peak and an increase in the dye emission peak upon increasing the solution dye:ZnO nanocrystal ratio, consistent with energy transfer from defect sites to adsorbed dye molecules. Time-resolved PL studies were used to quantify the energy transfer rate, the energy transfer efficiency, and the mean number of surface absorbed dyes. The authors claim, based on the magnitude of the energy transfer rate relative to the intrinsic defect PL decay rate, that a single nanocrystal can be quenched by a single dye molecule. Here I show, based on a critical analysis of particle size calibration curves2,3, that the number of absorbed dye molecules per nanocrystal is not reliable.
(1) Beane, G. A.; Morfa, A. J.; Funston, A. M.; Mulvaney, P. J. Phys. Chem. C 2012, 116 (5), 3305–3310.
(2) Wood, A.; Giersig, M.; Hilgendorff, M.; Vilas-Campos, A.; Liz-Marzán, L. M.; Mulvaney, P. Aust. J. Chem. 2003, 56 (10), 1051–1057.
(3) Brus, L. J. Phys. Chem. 1986, 90(12), 2555-2560.
Speaker: Zach Nilsson
Speaker Institution: Colorado State University
Event Date: 08-23-2017
Event Time: 4:00 PM
Event Location: Chemistry A101
Mixer Time: 3:45 PM
Mixer Location: Chemistry B101E
Host: J. Sambur