Center for Advanced Solar Photophysics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Nano Lett. 2012 Aug 8;12(8):4372-9. doi: 10.1021/nl302182u. Epub 2012 Jul 19.
The incorporation of copper dopants into II-VI colloidal nanocrystals (NCs) leads to the introduction of intragap electronic states and the development of a new emission feature due to an optical transition which couples the NC conduction band to the Cu-ion state. The mechanism underlying Cu-related emission and specifically the factors that control the branching between the intrinsic and impurity-related emission channels remain unclear. Here, we address this problem by conducting spectro-electrochemical measurements on Cu-doped core/shell ZnSe/CdSe NCs. These measurements indicate that the distribution of photoluminescence (PL) intensity between the intrinsic and the impurity bands as well as the overall PL efficiency can be controlled by varying the occupancy of surface defect sites. Specifically, by activating hole traps under negative electrochemical potential (the Fermi level is raised), we can enhance the Cu band at the expense of band-edge emission, which is consistent with the predominant Cu(2+) character of the dopant ions. Furthermore, we observe an overall PL "brightening" under negative potential and "dimming" under positive potential, which we attribute to changes in the occupancy of the electron trap sites (that is, the degree of their electronic passivation) that control nonradiative losses due to electron surface trapping.
铜掺杂剂掺入 II-VI 胶体纳米晶体（NCs）会导致引入带内电子态，并由于光学跃迁而开发出新的发射特性，该光学跃迁将 NC 导带与 Cu 离子态耦合。铜相关发射的机制，特别是控制本征和杂质相关发射通道之间分支的因素，仍然不清楚。在这里，我们通过对铜掺杂核/壳 ZnSe/CdSe NCs 进行光谱电化学测量来解决这个问题。这些测量表明，可以通过改变表面缺陷位点的占据来控制本征带和杂质带之间的光致发光（PL）强度分布以及整体 PL 效率。具体而言，通过在负电化学势下激活空穴陷阱（费米能级升高），我们可以增强 Cu 带，而牺牲带边缘发射，这与掺杂离子的主要 Cu(2+)特性一致。此外，我们在负电位下观察到整体 PL“变亮”，在正电位下观察到“变暗”，我们将其归因于电子俘获位点占据状态的变化（即，其电子钝化程度），这控制了由于电子表面俘获而导致的非辐射损耗。
