Ringlike emission profiles in scanning near-field photoluminescence images of single InGaAs quantum dots

In scanning near-field photoluminescence images of single InGaAs quantum dots taken with uncoated fiber tips, we observed sharp ringlike features varying in diameter with detection energy. This is in contrast to the typical single emission peaks observed using metal-coated fiber tips. These features can be explained by electrical charges induced by the uncoated fiber tip that lead to a Stark shift of the transition energy depending on the tip position. Simulations of the electric field at the quantum dot agree nicely with the experimental observation.