Dipole-forbidden energy transfer between CuCl quantum cubes via optical near-field

Summary form only given. The quantized exciton energy levels of (1,1,1) in a CuCl quantum cube (QC) X (4.6 nm) and (2,1,1) in a QC Y (6.3 nm) resonate with each other. For this type of resonant condition, the energy transfer time between QC via the optical near-field is estimated at 40 ps, assuming that the separation between two QCs is equal to 10 nm. This energy transfer time is much shorter than the exciton lifetime and is longer than the intersub-level transition /spl tau//sub sub/. Therefore, most of the exciton in a 4.6 nm CuCl QC transfer to the neighboring 6.3 nm QC. Here, we note that this energy transfer is optically forbidden, but becomes allowed with the optical near field. A far-field luminescence spectrum at 15 K is shown. It represents the luminescence intensity from large numbers of CuCl QCs, and is inhomogeneously broadened owing to the size distribution of the QCs. A near-field luminescence spectrum shows many fine structures are due to the contribution of the QCs near the apex of the near-field probe with a 50 nm aperture. The peaks X and Y correspond to the confined Z/sub 3/-exciton energy levels of the QCs with side lengths of 4.6 nm and 6.3 nm, respectively.