半导体纳米粒子在反胶束中的合成及其与芘分子间的跨相电子转移

本文在AOT/异辛烷反胶束中合成了CdS和ZnS半导体纳米粒子。粒子的荧光量子产率随胶束水含量的增大而减小。这可以归结为水含量增大导致胶粒表面Cd²⁺或Zn²⁺离子浓度降低,因为这两种离子在胶粒表面富集有利于形成硫空位,从而增大光生电子-空穴对的发光复合。研究发现,Ag⁺离子可以有效猝灭CdS和ZnS纳米粒子的荧光发射,该猝灭过程可以用Ag⁺离子在胶束中的Poisson分布来描述。以溶解在有机相中的pyrene作电子给体,在光激发下可以向CdS粒子注入电子,而和ZnS粒子间没有电荷转移发生,这可以解释为两种半导体的导带边相对于pyrene激发态氧化电位所处的位置不同。Cu²⁺或Ag⁺离子在ZnS颗粒表面吸附,可以形成Cu_xZn_1-xS或Ag_2xZn_1-xS复合粒子,降低ZnS粒子的导带位置,从而使之能够接受来自pyrene激发态的电子。实验结果证实了这种论点。

SYNTHESIS OF SEMICONDUCTOR NANOPARTICLES IN REVERSE MICELLES AND MICROHETEROGENEOUS ELECTRON-TRANSFER FROM PYRENE TO THESE PARTICLES

Semiconductor nanoparticles of CdS and ZnS have been synthesized in AOT-isooctane reverse micelles. It was found that the fluorescence quantum efficiency of the semiconductor particle decreases with increasing water content. This is attributed to the dilution of Cd²⁺ or Zn²⁺ ions at the interface of semiconductor particles. These cations favor the formation of sulfur vacancy, where the radiation recombination of the electron-hole pair occurs. The fluorescences of CdS and ZnS particles are effectively quenched by the addition of Ag⁺ ions.Such a process can be described by the Poisson statistics for the distribution of AG+ ions in reverse micelles. An efficient microheterogeneous electron-transfer was observed from pyrene to the CdS particles formed in AOT-isooctane reverse micelles,whereas no electrontransfer can be observed at ZnS particles. This is explained with considering the relative positions of the conduction bands of CdS and ZnS particles with respect to the oxidation potential of the excited singlet of pyrene. Adsorption of Cu²⁺ and Ag⁺ ions on the ZnS particle leads to the formation of mixed semiconductor particles, Cu_x-Zn_1-xS and Ag_2xZn_1-xS, the conduction bands of which are adjusted between those of ZnS and CuS or Ag₂S. Electrons can be injected from pyrene to these mixed particles. The efficiency of the electron-transfer is determined by the probability of the contact of pyrene with the semiconductor particles.