Uniform and well-dispersed photoluminescent semiconductor CdSe(Cadmium selenium) QDs(Quantum dots) were in-situ prepared stabilized by G4.0-NH2 PAMAM dendrimers in water and effects of metallic ions such as Zn2+, Cd2+, Cu2+, Ag+, Pb2+, 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 Cu2+ and Pb2+ because of the lower solubility of Ag2Se 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.