Deep level defect luminescence in cadmium selenide nano-crystals films

Undoped CdSe monocrystals and CdSe nano-crystals films have been studied at various temperatures by continuous wave (cw) photoluminescence. We report on a characteristic deep level emission, which is consistently observed in the wurtzite bulk- and nanocrystalline forms of CdSe. Two broad luminescence bands, which are separated from the excitonic emission by 0.5 and 0.7 eV occur in CdSe, prepared by quite different techniques. These bands experience, similar to the excitonic emission, a spectral shift to high energy enforced by the quantum confinement in nano-CdSe. The defects responsible for this luminescence are probably two different VCd-VSe divacancies: one is oriented along the hexagonal c-axis, the other is oriented along the basal Cd-Se bond directions.