Department of Chemical and Bimolecular Engineering (BK21+ Program), KAIST Institute for the Nanocentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea.
Nanotechnology. 2017 May 5;28(18):185603. doi: 10.1088/1361-6528/aa6828. Epub 2017 Apr 10.
We present facile synthesis of bright CdS/CdSe/CdS@SiO nanoparticles with 72% of quantum yields (QYs) retaining ca 80% of the original QYs. The main innovative point is the utilization of the highly luminescent CdS/CdSe/CdS seed/spherical quantum well/shell (SQW) as silica coating seeds. The significance of inorganic semiconductor shell passivation and structure design of quantum dots (QDs) for obtaining bright QD@SiO is demonstrated by applying silica encapsulation via reverse microemulsion method to three kinds of QDs with different structure: CdSe core and 2 nm CdS shell (CdSe/CdS-thin); CdSe core and 6 nm CdS shell (CdSe/CdS-thick); and CdS core, CdSe intermediate shell and 5 nm CdS outer shell (CdS/CdSe/CdS-SQW). Silica encapsulation inevitably results in lower photoluminescence quantum yield (PL QY) than pristine QDs due to formation of surface defects. However, the retaining ratio of pristine QY is different in the three silica coated samples; for example, CdSe/CdS-thin/SiO shows the lowest retaining ratio (36%) while the retaining ratio of pristine PL QY in CdSe/CdS-thick/SiO and SQW/SiO is over 80% and SQW/SiO shows the highest resulting PL QY. Thick outermost CdS shell isolates the excitons from the defects at surface, making PL QY relatively insensitive to silica encapsulation. The bright SiO-coated SQW sample shows robustness against harsh conditions, such as acid etching and thermal annealing. The high luminescence and long-term stability highlights the potential of using the SQW/SiO nanoparticles in bio-labeling or display applications.
我们提出了一种简便的方法来合成具有 72%量子产率（QYs）的亮 CdS/CdSe/CdS@SiO 纳米粒子，保留了原始 QYs 的 80%左右。主要的创新点是利用高度发光的 CdS/CdSe/CdS 种子/球形量子阱/壳（SQW）作为二氧化硅涂层种子。通过反相微乳液法将二氧化硅封装应用于三种具有不同结构的量子点（QDs）：CdSe 核和 2nmCdS 壳（CdSe/CdS-薄）；CdSe 核和 6nmCdS 壳（CdSe/CdS-厚）；以及 CdS 核、CdSe 中间壳和 5nmCdS 外壳（CdS/CdSe/CdS-SQW），证明了无机半导体壳层钝化和量子点结构设计对于获得亮 QD@SiO 的重要性。由于形成表面缺陷，二氧化硅封装不可避免地导致光致发光量子产率（PLQY）低于原始 QD。然而，在三种二氧化硅涂层样品中，原始 QY 的保留率不同；例如，CdSe/CdS-薄/SiO 显示出最低的保留率（36%），而 CdSe/CdS-厚/SiO 和 SQW/SiO 中的原始 PLQY 的保留率超过 80%，并且 SQW/SiO 显示出最高的 PLQY。最外层的厚 CdS 壳将激子与表面缺陷隔离开来，使得 PLQY 相对不受二氧化硅封装的影响。亮的 SiO 涂层 SQW 样品在苛刻的条件下具有很强的稳定性，例如酸刻蚀和热退火。高发光度和长期稳定性突出了 SQW/SiO 纳米粒子在生物标记或显示应用中的潜力。
