Uncovering forbidden optical transitions in PbSe nanocrystals
Résumé
The 1Sh,e−1Pe,h exciton transition energy of PbSe nanocrystals was determined via two-photon photoluminescence excitation spectroscopy and was found to be in good agreement with predictions from a tight-binding calculation. The two-photon excitation peak occurs at energies very close to a strong feature in the one-photon absorption spectrum and suggests that it should be assigned as a formally forbidden S−P transition. Leading explanations for the unusual strength of the forbidden transition are discussed.