Ohara Yuhki, Nakabayashi Takakazu, Iwasaki Kentaro, Torimoto Tsukasa, Ohtani Bunsho, Hiratani Takayuki, Konishi Katsuaki, Ohta Nobuhiro
Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan.
J Phys Chem B. 2006 Oct 26;110(42):20927-36. doi: 10.1021/jp064205r.
Electric-field-induced changes in absorption and emission spectra of colloidal CdS nanoparticles ranging in size from 1.0 to 5.0 nm in diameter have been measured by using electric field modulation spectroscopy. The analysis of the electroabsorption spectra indicates that the dipole moment in the first exciton state becomes larger with increasing particle size. The presence of the large dipole moment following photoexcitation into the first exciton band suggests that the CdS nanoparticles have large CT character in the first exciton state. The quantum yields both of the exciton emission and of the trap emission are markedly reduced by application of an electric field. On the basis of the direct measurements of the field-induced change in emission decay profile, it is suggested that the field-induced de-enhancement of these emission yields results from the field-induced decreases both in lifetime and in initial population of each emitting state. It is also found that the emission intensity of CdS nanoparticles increases under the UV light irradiation in air and decreases in a vacuum condition and that fluorescence lifetime in the former case is longer than that in the latter. This enhancement and de-enhancement process in emission intensity is almost reversible at least in several cycles.
通过电场调制光谱法测量了直径在1.0至5.0纳米范围内的胶体硫化镉纳米颗粒在电场诱导下的吸收光谱和发射光谱变化。对电吸收光谱的分析表明，第一激子态的偶极矩随粒径增大而增大。光激发进入第一激子带后出现的大偶极矩表明，硫化镉纳米颗粒在第一激子态具有较大的电荷转移（CT）特性。施加电场会显著降低激子发射和陷阱发射的量子产率。基于对场诱导发射衰减曲线变化的直接测量，表明这些发射产率的场诱导去增强是由于场诱导导致每个发射态的寿命和初始粒子数减少。还发现，硫化镉纳米颗粒的发射强度在空气中紫外光照射下增加，在真空条件下降低，并且前一种情况下的荧光寿命比后一种情况长。发射强度的这种增强和去增强过程至少在几个循环中几乎是可逆的。
