Toufanian Reyhaneh, Chern Margaret, Kong Victoria H, Dennis Allison M
Division of Materials Science and Engineering, Boston University, Boston, MA 02215, USA.
Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
Chem Mater. 2021 Mar 23;33(6):1964-1975. doi: 10.1021/acs.chemmater.0c03181. Epub 2021 Mar 5.
The size-dependent optoelectronic properties of semiconductor nanocrystals quantum dots (QDs) are hugely beneficial for color tunability but induce an inherent relative PL brightness mismatch in QDs emitting different colors, as larger emitters absorb more incident photons than smaller particles. Here, we examine the effect of core composition, shell composition, and shell thickness on optical properties including high energy absorption, quantum yield (QY), and the relative brightness of InP/ZnS and InP/ZnSe core/shell and InP/ZnSe/ZnS core/shell/shell QDs at different excitation wavelengths. Our analysis reveals that the presence of an intermediate ZnSe shell changes the wavelength of enhanced absorption onset and leads to highly excitation wavelength dependent QYs. Switching from commercial CdSe/ZnS to InP/ZnS reduces the brightness-mismatch between green and red emitters from 33- to 5-fold. Incorporating a 4-monolayer thick optically absorbing ZnSe shell into the QD heterostructure and heating the QDs in a solution of zinc oleate and trioctylphosphine produces InP/ZnSe/ZnS QDs that are ~10-fold brighter than their InP/ZnS counterparts. In contrast to CdSe/CdS/ZnS core/shell/shell QDs, which only photoluminesce at red wavelengths with thicker CdS shells due to their Quasi-Type II bandstructure, Type I InP/ZnSe/ZnS QDs are uniquely suited to creating a rainbow of visible-emitting, brightness matched emitters. By tailoring the thickness of the intermediate ZnSe shell, heavy metal-free, brightness-matched green and red emitters are produced. This study highlights the ability to overcome the inherent brightness mismatch seen in QDs through concerted materials design of heterostructured core/shell InP-based QDs.
半导体纳米晶体量子点（QDs）的尺寸依赖性光电特性对颜色可调性极为有利，但会在发射不同颜色的量子点中引发固有的相对光致发光（PL）亮度失配，因为较大的发射体比较小的粒子吸收更多的入射光子。在此，我们研究了核组成、壳组成和壳厚度对光学特性的影响，包括高能吸收、量子产率（QY），以及不同激发波长下InP/ZnS和InP/ZnSe核/壳及InP/ZnSe/ZnS核/壳/壳量子点的相对亮度。我们的分析表明，中间ZnSe壳的存在改变了增强吸收起始波长，并导致量子产率高度依赖激发波长。从商用CdSe/ZnS切换到InP/ZnS可将绿色和红色发射体之间的亮度失配从33倍降低到5倍。将4单层厚的光学吸收性ZnSe壳纳入量子点异质结构，并在油酸锌和三辛基膦溶液中加热量子点，可产生比其InP/ZnS对应物亮约10倍的InP/ZnSe/ZnS量子点。与CdSe/CdS/ZnS核/壳/壳量子点不同，由于其准II型能带结构，只有在具有较厚CdS壳时才在红色波长处光致发光，I型InP/ZnSe/ZnS量子点特别适合创建一系列可见发射、亮度匹配的发射体。通过调整中间ZnSe壳的厚度，可生产出无重金属、亮度匹配的绿色和红色发射体。这项研究突出了通过对基于InP的异质结构核/壳量子点进行协同材料设计来克服量子点中固有亮度失配的能力。
