Control of the Morphology of Complex Semiconductor Nanocrystals with a Type II Heterojunction, Dots vs Peanuts, by Thermal Cycling

Abstract

Type II CdSe/CdTe core/shell nanocrystals with a dot shape were synthesized using a modified SILAR technique that incorporates cycling of the reaction temperature (thermal cycling). Conversely, experimental results revealed that the standard SILAR alone produced type II core/shell nanocrystals in a peanut shape (1D). Despite their differences in shape, the optical properties observed for the type II dot- and peanut-shaped core/shell nanocrystals were similar. The dot-shaped nanocrystals were confirmed as core/shell structures with an abrupt type II heterojunction within the experimental accuracy, and the peanut-shaped ones were found to be consistent with CdSe and CdTe separated on the two ends of the rods. Similar techniques were used for the synthesis of CdS/CdSe/CdTe type II colloidal quantum well heterostructures with dot and peanut shapes. For these type II colloidal quantum well structures, the PL peak positions were shown to be readily tunable by varying the CdSe and CdTe shell thickness, something not typically seen for the quantum dots. The PL quantum yield of these nanocrystals were found to range between 30 and 60%.

Bright and Water-Soluble Near IR-Emitting CdSe/CdTe/ZnSe Type-II/Type-I Nanocrystals, Tuning the Efficiency and Stability by Growth

“…7 As mentioned above, attempts to generate water-soluble CdSe/ CdTe core/shell nanocrystals failed. This is probably because of the hole trapping by the negatively charged thiolate ligands bounded on the surface of the CdTe shell.…”

“…In attempts to further boost the PL QY, type-II heterojunctions were examined using both quantum dots and quantum shell nanocrystals as the starting materials for the formation of the type-II nanocrystals, each of which was tested with a variety of shell thicknesses and sizes. 7 In all of these attempts, one interesting point is that straight SILAR always ended up either with minimum growth of the shell or forming peanut-shaped heterojunction nanocrystals, and SILAR-TC yielded the type-II core/shell dots or core/shell/shell type-I/type-II dots. Unfortunately, 30% PL QY was about the highest for stable dots, however up to 50% PL QY was observed for unstable ones.…”

Design and preparation of quantum dots fluorescent probes for in situ identification of Microthrix parvicella in bulking sludge

“…It could be seen that the three prepared QDs probes had different particle sizes, 4.5 nm for probe A, 2.9 nm for probe B, and 3.1 nm for probe C, and they dispersed well. Moreover, the morphologies of the three QDs probes were of dot-shaped heteronanostructures, which was a benefit for the high-fluorescence quantum yields in aqueous media (Blackman et al 2008;Blackman et al 2007;Gui and An 2013). In the high-resolution TEM images of the three QDs probes, it could be found that the crystal lattice of probe A was more clear than that of probes B and C, suggesting that in the preparation of probes B and C, the long carbon chain affected the crystallinity of the CdTe/CdS QDs, which was consistent with the XRD analysis results.…”

Prepare core–multishell CdSe/ZnS nanocrystals with pure color and controlled emission by tri-n-octylphosphine-assisted method

“…Orange-colored CdSe QDs were used as core for synthesizing the core-shell QDs according to the modified SILAR procedure [16,17] and the modified TOP-assisted method [21].…”

“…In particular, successive ionic layer adsorption and reaction (SILAR) is the most widely used method [7,16,17]. However, the intrinsic strain-induced formation of misfit dislocations and the defects within the shell cannot be avoided by SILAR method, which results in the decrease of QY as the shell thickness increasing [6,8,18].…”