利用飞秒激光Z-扫描与泵浦-探测技术, 研究了室温下ZnO/ZnS与ZnO/ZnS/Ag核-壳胶体量子点的双光子吸收效应。研究发现: ZnO基核-壳量子点的本征双光子吸收系数比ZnO体材料增大了3个数量级; 测量得到的660 nm处的ZnO/ZnS核-壳量子点双光子吸收截面约为4.3×10-44 cm4·s·photon-1, 比相应的ZnS、ZnSe及 CdS量子点大2个数量级; 当ZnO/ZnS核-壳量子点镶嵌了银纳米点时, 非线性吸收有所增强。ZnO基复合纳米结构的双光子吸收增强可归因于量子限域与局域场效应。

We report a large two-photon absorption (TPA) in ZnO/ZnS and ZnO/ZnS/Ag core/shell quantum dots (QDs). Z-scan and pump-probe techniques with femtosecond laser pulses were employed to characterized the quantum dots. The intrinsic TPA coefficients of ZnO-based core/shell QDs are enhanced with nearly three orders of magnitude compared to that of ZnO bulk counterpart, which is attributable to quantum confinement effect. The TPA cross-section of ZnO-based nanocomposites is determined to be ~4.3×10-44 cm4·s·photon-1 at the wavelength of 660 nm. This value is at least two orders of magnitude greater than that of ZnS, ZnSe, and CdS QDs. Due to the local field effect, the nonlinear absorption in ZnO/ZnS core/shell QDs is improved as beaded with Ag nano-dots.