Highly luminescent silica-coated CdS/CdSe/CdS nanoparticles with strong chemical robustness and excellent thermal stability

Abstract

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.

Highly Stable, Near‐Unity Efficiency Atomically Flat Semiconductor Nanocrystals of CdSe/ZnS Hetero‐Nanoplatelets Enabled by ZnS‐Shell Hot‐Injection Growth

“…When they performed temperature stability test with the pristine core/shell NCs, their core/shell NCs can retain only 61% of their initial emission at 473 K and almost quenched emission at 573 K . Regarding the InP based QDs, in their work the authors studied the thermal stability of InP/ZnS up to 800 K and the results demonstrated that integrated PL of these NCs decreased to almost 10% of their initial value at around 500 K . In our study, owing to the effective protection of the core surface with thick ZnS shell, trap states are passivated and hence HI thick‐shell NPLs not only exhibit the best performance among the reported NPL samples, but also have a comparable thermal stability even with the previously reported colloidal 0D quantum dots, although having relatively higher surface to volume ratio …”

3D test sample for the calibration and quality control of super-resolution and confocal microscopes

“…This seeded growth method is directly compatible with the work presented here, because silica coating is performed in the same reverse micro-emulsion system used to synthesize the fluorescent cores. The most promising quantum dots to use are so-called CdS/CdSe/CdS quantum well dots, as these can be coated with silica while maintaining a high photoluminescence quantum yield 46,47 .…”

Classification, Synthesis, and Application of Luminescent Silica Nanoparticles: a Review

“…When the fluorophores are hydrosoluble, it is easy to form a homogeneous silica layer on the surface within the molecules in the droplet. Nianfang Wang et al [46] synthesized luminescent silica-coated CdS/CdSe/CdS nanoparticles via reverse microemulsion method. Figure 13 showed the TEM images of the synthetic QDs and QDs@SiO 2 .…”