金属离子对CdS量子点/聚酰胺-胺树形分子纳米复合材料光致发光性能的影响

以聚酰胺-胺树形分子为模板制备了分散好、尺寸均匀的CdS量子点，并用分光光度滴定法研究了Cd²⁺、Zn²⁺、Pb²⁺、Cu²⁺、Mn²⁺几种金属离子对其光致发光性能的影响。发现不同离子对CdS量子点的发光性能影响不同:Cd²⁺和Zn²⁺使量子点荧光增强，Pb²⁺、Cu²⁺和Mn²⁺使其荧光有不同程度淬灭。这归因于金属离子对CdS量子点表面的修饰作用。Cd²⁺能减少由S^2-悬键构成的非辐射复合中心，增强树形分子对量子点表面缺陷的钝化作用，并能在量子点周围形成类肖特基能垒，从而显著增大CdS量子点的光致发光效率。由于ZnS与CdS的晶格参数非常接近，Zn²⁺能起到与Cd²⁺类似的作用，使CdS量子点的发光效率大大增强。Pb²⁺和Cu²⁺能取代Cd²⁺在CdS量子点表面生成窄带隙的壳层，对其发光有很强的淬灭作用。由于块体PbS的带隙比块体CuS窄，故Pb²⁺的淬灭能力强于Cu²⁺。Mn²⁺能破坏Cd²⁺与PAMAM树形分子的配位键，降低树形分子对CdS量子点表面缺陷的钝化作用，且其本身在量子点表面构成了新的荧光淬灭中心，但Mn²⁺也能形成较弱的类肖特基能垒，故对量子点的发光淬灭作用较弱。

Effects of Metallic Ions on the Photoluminescence Properties of CdS Quantum Dots/Poly(amidoamine) Dendrimer Nano-composites

CdS quantum dots(QDs) were prepared using poly(amidoamine) (PAMAM) dendrimer template,and eff-ects of such metallic ions as Cd2 ,Zn2 ,Pb2 ,Cu2 ,Mn2 on the photoluminescence(PL) properties of CdS QDs were studied using spectrophotometric titration. The results show that Cd2 and Zn2 ions enhance the PL intensity of CdS QDs,while Pb2 ,Cu2 and Mn2 ions quench it. These are attributed to the surface modification of metallic ions on CdS QDs. Excess Cd2 ions can reduce the non-recombination centres,increase the passivation of PAMAM dendrimers on the surface of CdS QDs,and form a Schottky-like barrier which enhances the PL efficiency greatly. Excess Zn2 ions can also increase the PL intensity markedly in the same way as Cd2 ions because of their similar lattice parameters. However,a PbS or CuS shell on CdS QDs emerges due to the substitution of Cd2 ,which leads to the decrease of band-edge emitting of CdS QDs. And the quenching effect of Pb2 is stronger than Cu2 . The coordination between Cd2 and dendrimers can be damaged by Mn2 ions,which results in weaker passivation of the QDs surface detects. Since Mn2 ions themselves are new quenching centres,the quenching effect is mild in spite of a lower-energy Schottky-like barrier formed by Mn2 ions.