Measurement of the separation dependence of resonant energy transfer between cadmium selenide/zinc sulfide

An apparatus has been built to study the separation dependence of the interaction between small and large resonant groups of CdSe/ZnS nanocrystallite quantum dots (NQDs). A near-field scanning optical microscope (NSOM) is used to bring a group of mono-disperse 6 nm diameter dots close (near-field range) to a 8 nm diameter group of dots which are deposited on a solid immersion lens. 3rd excited excitonic energy level of large NQD does match the ground excitonic energy level of small NQDs. Combination of spectral and positional filtering allows us to measure the interaction between small numbers of NQDs, with the ultimate goal of identifying the interaction between individual dots. Quenching of the small NQDs photoluminescence signal has been observed as the small NQDs get to close proximity of large NQDs. Separation between two groups of the NQDs was changing in the range of 15-40nm during the experiment. The transition probability between these two groups of NQDs is theoretically obtained to be (2.72x10--47m 6)=R6. Forster radius, as a signature of energy transfer efficiency is extracted from experimental data to be 17 nm.