Effects of metallic ions on photoluminescence properties of CdSe/PAMAM nanocomposites and their application in fingerprint detection

Uniform and well-dispersed photoluminescent semiconductor CdSe(Cadmium selenium) QDs(Quantum dots) were in-situ prepared stabilized by G4.0-NH ₂ PAMAM dendrimers in water and effects of metallic ions such as Zn²⁺, Cd²⁺, Cu²⁺, Ag⁺, Pb ²⁺, K⁺, Na⁺ on the photoluminescence(PL) properties of CdSe QDs were studied using spectrophotometric titration. The results show that Zn²⁺ and Cd²⁺ ions enhance the PL intensity of CdSe QDs, Cu²⁺, Ag⁺ and Pb²⁺ ions quench the PL intensity, while K⁺ and Na⁺ ions have no obvious effects. Those are attributed to the surface modification of CdSe QDs. Excess Cd²⁺ ions can reduce the non-combination centers, increase the passivation of PAMAM on the surface of CdSe QDs, and form a Schottky-like barrier which enhanced the PL efficiency. Excess Zn²⁺ ions can also increase the PL intensity of CdSe QDs in the same way as Cd²⁺ ions because of the much similar lattice parameters of CdSe and ZnSe. However, a CuSe, Ag₂Se or PbSe shell on CdSe QDs emerges due to the substitution of Cd²⁺ ions, which leads to the decrease of band-edge emmiting of CdSe QDs. and the quenching effect of Ag⁺ is stonger than Cu ²⁺ and Pb²⁺ because of the lower solubility of Ag ₂Se formed on the surface of CdSe QDs. Oil latent fingerprints deposited on tinfoil surface treated with CdSe/dendrimer NCs(Nanocomposites) Cd²⁺-CdSe/ PAMAM NCs and Zn²⁺-CdSe /PAMAM NCs emitted bright yellow photoluminescence under ultraviolet excitation of 365nm from an UV LED in the dark., among, fingerprint treated with Cd²⁺-CdSe/ dendrimer NCs and Zn²⁺-CdSe /PAMAM NCs was detected with better resolving rate.