Measurement of the separation dependence of resonant energy transfer between CdSe/ZnS core/shell nanocrystallite quantum dots

TL;DR

This study investigates how the resonant energy transfer between CdSe/ZnS quantum dots depends on their separation distance, using near-field microscopy and optical measurements to quantify transfer efficiency and transition probabilities.

Contribution

It provides experimental measurements of the separation dependence of energy transfer between quantum dots, including transition probabilities and F"orster radius, with numerical analysis of energy levels.

Findings

Energy transfer transition probability scales as 1/R^6.

F"orster radius is experimentally determined to be 14-22 nm.

Photoluminescence quenching observed as dots approach each other.

Abstract

The separation dependence of the interaction between two resonant groups of CdSe/ZnS nanocrystallite quantum dots is studied at room temperature. A near-field scanning optical microscope is used to bring a group of mono-disperse ~6.5 nm diameter nanocrystallite quantum dots which are attached to the microscope probe, into close proximity of `~8.5 nm diameter group of nanocrystallite quantum dots which are deposited on a solid immersion lens. Information extracted from photoluminescence, photoluminescence excitation and absorption curves as well as numerical calculations of the energy levels, show that the third excited excitonic energy level of the large quantum dots nearly matches the ground excitonic energy level for the small quantum dots. Quenching of the small quantum dots photoluminescence signal has been observed as they approach the large quantum dots. On average, the separation between microscope probe and solid immersion lens changed in the 15-50 nm range. The transition probability between these two groups of quantum dots is calculated to be (2.60 x 10-47 m6)/R6, within the (0.70 x 10-47 m6)/R6 - (11.0 x 10-47 m6)/R6 experimentally obtained range of transition probabilities. The F\"orster radius, as a signature of energy transfer efficiency, is experimentally found to be in the 14-22 nm range.