Sequential Synthesis of Type II Colloidal CdTe/CdSe Core–Shell Nanocrystals

Abstract

Colloidal type II CdTe/CdSe nanocrystals were synthesized by sequential addition of a tri-n-octylphosphine telluride (TOPTe)/TOP solution and several shell-precursor solutions to a CdO/TOP solution; the shell-precursor solutions consisted of CdO and TOPSe in TOP. For the growth of the CdTe core, the TOPTe/TOP solution was swiftly added to the CdO/TOP solution at a higher temperature (300 degrees C) than the growth temperature (250 degrees C). For the growth of the CdSe shell, in contrast, the CdO/TOPSe/TOP solution was slowly added to the CdTe/TOP solution at a lower temperature than the growth temperature (200-240 degrees C). The temporal evolution of the optical properties of the growing core-shell nanocrystals was monitored in detail. During the growth of the CdSe shell, the core-shell nanocrystals exhibited interesting changes in photoluminescence (PL) properties. The highest PL efficiency (approximately 38 %) was detected from core-shell nanocrystals with a CdSe shell thickness of 0.4-0.5 nm (indicated by TEM); the formation of the first monolayer is proposed. Our synthetic approach is well suited to a practical realization of engineering materials with bandgaps in the near-IR and IR spectral ranges.

Spectroscopy and Femtosecond Dynamics of Type‐II CdTe/CdSe Core–Shell Quantum Dots

“…As shown in Figure 2 a, the appearance of the Se peak at 1.4 keV, in combination with the increase of the ratio for Cd versus Te from 1.2:1 in CdTe to % 6:1 in CdTe/CdSe, indicates the formation of CdSe. As shown in Figure 2 b, comparing the X-ray diffraction (XRD) pattern of the CdTe core, two sets of peaks at faces [ [112] shift to higher scattering angle upon coating with the CdSe shell, the results of which are consistent with those reported by Yu et al [10] In addition, alloy, if it formed, should be supported by a narrowing full-width-at-half-maximum (FWHM) in the set of peaks at [100], [002] and [101]. In contrast, a slight increase of the FWHM was observed upon encapsulating CdSe, supporting the suggestion of the formation of a CdTe/CdSe core/shell structure.…”

“…[9] Very recently, a synthetic route to prepare CdTe/CdSe colloidal using a template without incorporating fatty acid, amines, or phosphine oxide was reported. [10] In another approach, interconversion between type-I and II QDs has been achieved via fixing the ZnSe core radius, while increasing the shell (CdSe) thickness. [11] In terms of applications, type-II QDs have been exploited successfully as near-infrared (NIR) dyes for biomedical imaging in living tissue by taking advantage of their great photostability and deeper light penetration.…”

Low-Temperature Approach to Highly Emissive Copper Indium Sulfide Colloidal Nanocrystals and Their Bioimaging Applications

“…Such an increase from Sample 5 (120°C/15 min) to Sample 11 (160°C/120 min) is similar to what was observed during the growth of Zn x Cd 1−x S gradiently alloyed QDs 43 and CdTe/CdSe core−shell QDs. 44 Figure S1B in the Supporting Information demonstrates the good synthetic 3 -to-4SDPP feed molar ratios. The growth was at 160°C for 120 min, and the PL QY was estimated to be ∼23% for the as-synthesized NCs.…”

The Preparation and Application of Dendrimer Modified CdTe/CdS Near Infrared Quantum Dots for Brain Cancer Cells Imaging

“…In the PL spectrum, the CdTe QDs exhibited emission at 562 nm with the excitation wavelength set of 365 nm. Compared to CdTe QDs, the emission wavelength of dendrimer modified core/shell CdTe/CdS QDs shifted to 650 nm which has been taken as a feature of QDs with spatial separated charge carriers [12]. Furthermore, the excitoinc peak of the core/shell CdTe/CdS QDs shifted to shorter wavelength companying with increasing the generations of dendrimers.…”