Enhanced Valley Splitting of Exciton Emission in Colloidal PbSe Quantum Dots When the Interdot Distance Coincides with Onset of Forster Resonance Energy Transfer

Photoluminescence (PL) emission of colloidal PbSe/CdSe core/shell quantum dots (QDs, CdSe shell thickness: 0.2 nm) at the lowest exciton state was investigated at room temperature and varying inter-QD distance (L = 7-240 nm) by changing the QD concentration. A distinct enhancement of the valley splitting of PbSe QDs was observed upon reducing L. Simultaneously, there was a redshift in the emission due to Forster resonance energy transfer (FRET), when the L value was still sufficiently large (7 nm <= L <= 50 nm) so that the wave functions of different QDs do not overlap. The enhanced valley splitting under no apparent external field is quite interesting as a method to control the valley splitting. The electronic coupling leading to FRET may enhance the valley splitting, because it occurs in an identical range of L.

Automated summary

The research found that the valley splitting of PbSe quantum dots can be significantly enhanced by controlling the thickness of the CdSe shell in varying inter-QD distances. When the inter-QD distance is large, Forster resonance energy transfer causes a redshift in photoluminescence emission.