Tunable photoluminescent Cu-doped CdS/ZnSe type-II core/shell quantum dots

Abstract

We used wet chemical methods to fabricate CdSm/ZnSen type-II core/shell (C/S) quantum dots (QDs) doped with different Cu contents (x), where m is the index related to the size (d) of the CdS core and n is the number of monolayers of the ZnSe shell. X-ray diffraction analyses indicated that all QDs crystallized in the zinc blende structure. The formation of type-II heterostructures was confirmed by Raman scattering spectroscopy. Studying the photoluminescence (PL) properties, we have found PL spectra of QDs showing two emissions. The first one is associated with the near band-edge excitonic transition of type-II C/S structures while the other is mainly associated with the Cu2+ impurity. We have also found that the Cu2+ level in C/S QDs is stable versus varying n and occupies above the valence bands of CdS and ZnSe. Particularly, by changing the values of d (or m), n, and x in the core and shell parts, we would tune effectively both emission intensity and peak position. While the exciton emission could be tuned from 495 to about 615 nm, the Cu-related emission could be from 700 to about 945 nm. Also, the lifetime related to the Cu emission of the doped C/S QDs also enhances remarkably. We believe that these Cu-doped CdS/ZnSe type-II C/S QDs are potential for near-infrared applications.