Two distinct photoluminescence responses of CdTe quantum dots to Ag (I)

Four sizes of water-soluble thiol-capped CdTe quantum dots (QDs) have been synthesized and used to investigate the photoluminescence (PL) responses to Ag+ ions. For small particles, the CdTe QDs exhibit PL enhancement in the presence of lower concentration of Ag+ but show obvious quenching with the further increase of Ag+; for larger particles, however, PL of CdTe QDs is quenched all the time with the Ag+ addition, no PL enhancement is observed. Mechanism study shows that small QDs with more traps on the particle surface are effectively passivated by initial adsorbed Ag+, which accounts for the PL enhancement observed; after the initial traps are saturated, the excess Ag+ facilitates nonradiative recombination, resulting in PL quenching. For larger particles, the nonradiative recombination dominates the whole process even for the lower concentration of Ag+, due to the fewer traps on the QD surface. Compared with larger particles, the small CdTe QDs are more suitable for sensing Ag+ because of the more sensitive and selective PL response. To our best knowledge, this is the first systematical study on the interaction of Ag+ with different-sized CdTe QDs.