Manifestations of Varying Grading Level in CdSe/ZnSe Core–Shell Nanocrystals

Abstract

Graded interface core–shell nanocrystals (NCs) are being investigated to attain highly luminescent systems and are also anticipated to be “blinking-free” at the single-particle level. In the present work, CdSe/ZnSe-graded core–shell NCs with varying confinement potential profile are studied at the single-particle level. The internal structure of NCs is determined with the aid of optical, structural, and chemical probes. Notably, the radiative lifetime for different nanostructures decays monoexponentially. The variation in the radiative lifetime due to differing internal structure is understood on the basis of recently reported first-principles study on different interfaces of core–shell NCs, in particular attributed to varying overlap of electron–hole wave functions. The single NC measurements reveal that the percentage of nonblinking NCs is higher for slowly varying confinement potential. Statistically suppressed blinking (∼80%) and a single exponential PL decay curve, accompanied by a very narrow (∼30 meV) emission line at the single NC level, are observed in graded CdSe/ZnSe core–shell NCs.

Continuous‐wave laser irradiation to form Cd1−xZnxSe shell on CdSe QDs in silicate glasses

“…In addition, our glass has a large concentration of ZnO. Similar concentrations of Zn in Cd 1−x Zn x Se also have been reported in several previous works both from the glass matrix as well as from QDs prepared by the colloidal processes …”

Reply to the comments on “Continuous‐wave laser irradiation to form Cd1−xZnxSe shell on CdSe QDs in silicate glasses”

“…However, we observed a large decrease in the defect emission ( λ ≈ 620 nm) together with a blue‐shift in the band‐edge emission (Figure 2B). A similar decrease in the defect emission was reported for other studies of QDs with shell structures produced by colloidal processing . The blue‐shift in the band‐edge emission provides additional indirect evidence of the shell structure since a blue‐shift should result from the decrease in the size of CdSe QDs as the surface of CdSe QDs transforms to Cd 1‐ x Zn x Se as cation exchange progresses .…”

“…A similar decrease in the defect emission was reported for other studies of QDs with shell structures produced by colloidal processing. [1][2][3] The blue-shift in the band-edge emission provides additional indirect evidence of the shell structure 1 since a blue-shift should result from the decrease in the size of CdSe QDs as the surface of CdSe QDs transforms to Cd 1-x Zn x Se as cation exchange progresses. 2,3 If homogeneous Cd 1−x Zn x Se alloy QDs have formed, as authors of the comment propose, the defect emission due to the interfaces should remain and the band gap emission will be red-shifted as the QDs grow during the laser irradiation.…”

“…[1][2][3] The blue-shift in the band-edge emission provides additional indirect evidence of the shell structure 1 since a blue-shift should result from the decrease in the size of CdSe QDs as the surface of CdSe QDs transforms to Cd 1-x Zn x Se as cation exchange progresses. 2,3 If homogeneous Cd 1−x Zn x Se alloy QDs have formed, as authors of the comment propose, the defect emission due to the interfaces should remain and the band gap emission will be red-shifted as the QDs grow during the laser irradiation. Additional support for the formation of core-shell QDs is provided by the increase in the lifetime of the band gap emission, which is presumably due to a decrease in nonradiative processes with the formation of the Znrich shell (Figure 7).…”

Insights on heterogeneity in blinking mechanisms and non-ergodicity using sub-ensemble statistical analysis of single quantum-dots

“…1(a) shows representative traces from three such individual QDs, being either mostly, moderately, or rarely emissive over the duration of data acquisition. Several other NC systems, 29,[43][44][45][46][47][48] including CdSe-ZnSe alloy core-shell QDs 49 of similar size (Fig. 1(b)) also exhibit such contrasting blinking characteristics in terms of time-averaged intensity distributions, albeit the fraction of different sub-populations may vary.…”