硫族化镉纳米微晶由于具有发光效率高和发射波长可调谐等优良性质在光电器件中有重要的应用,CdSe/CdS点-棒异质结量子点是典型代表之一。本文中通过非共振拉曼方法探测了该量子点在5~50 cm-1的声学声子模,利用不同模式的偏振特性,清晰地指认了球状核壳异质结量子点的扭转模式和径向呼吸模、棒状和点-棒异质结量子点的伸缩模和径向呼吸模等,并观察到了棒状量子点和点-棒异质结量子点的电子拉曼散射。同时发现点-棒异质结量子点的径向呼吸模较尺寸相当的纳米棒量子点发生红移。利用有限元方法形象模拟各量子点声学模的振动形式,并发现点-棒异质结量子点呼吸模振动的局域性。随后,引入局域有效声速的概念,利用改进的Lamb定律,成功解释了该红移是由CdSe核区域声速的减小所导致的,并再次验证该呼吸模局域在核附近区域。该研究对于表征和研究量子点中的限制性声学模具有重要意义,声学模和光学跃迁均局域在量子点附近区域的特性,对调控其激子-声子耦合和相关的光学性质具有重要指导意义。

Colloidal semiconductor nanocrystals(NCs) in particular nanorods,further the heterostructured nanocrystals have created tremendous interest to date due to their unique optical properties,such as efficient and tunable light emission via size control as well as the simple fabrication.CdSe/CdS dot-in-rods is one of the most typical specimen,whose absorptions depend on the nanorod shell while the emitting wavelength is determined by the core size.In this letter,acoustic vibrations(5-50 cm-1) of CdSe quantum dots,CdSe/CdS core-shell quantum dots with giant shell,CdS nanorods and CdSe/CdS dot-in-rods that consist of a CdSe core and a rod-shaped CdS shell are studied by non-resonant Raman spectroscopy.The phonon modes in the ULF region can be clearly assigned by their polarization behavior and Lamb’s theory to extensional and breathing modes of the NCs.The electronic Raman scattering is observed in rods and dot-in-rods in the meanwhile.Furthermore,in dot-in-rods the dominant RBM is red-shifted with respect to bare nanorods,which can be analyzed quantitatively in terms of local reduction of sound velocity.Finite element simulations using Comsol software reveal the intricate distribution of strain induced by the acoustic vibrations,and particularly the localization of the RBM in the core region in core-shell architectures.The localization of the acoustic phonons in certain regions of the rod influences their resonant frequency,which together with their spatial overlap with the electron and hole wave functions can be expected to affect coupling to band edge excitons,and therefore impact their light emitting properties.