Photoluminescence Properties of Self-Assembled Monolayers Of CdSe and CdSe/ZnS Quantum Dots

The photoluminescence (PL) properties of self-assembled monolayers (SAMs) of CdSe and CdSe/ZnS quantum dots (QDs) were investigated. From measurements of the temperature dependence of PL spectra, it is demonstrated that the thiol group, which is a constituent of the reagent for formation of the SAM, degrades the PL properties during the SAM formation process. With an additional dipping treatment in a Cd(CIO4)(2) aqueous solution with pH = 10, the band-edge PL intensity is increased remarkably. The improvement of PL properties is attributed to QD surface modification with a Cd(OH)2 layer. On the other hand, the defect-related PL band is not observed at all, even at 10 K, in the SAMs of CdSe/ZnS core/shell QDs. This fact indicates that the ZnS shell layer prevents degradation of the PL properties during the SAM process.