Influence of Interface-Driven Strain on the Spectral Diffusion Properties of Core/Shell CdSe/CdS Dot/Rod Nanoparticles

Abstract

By combining an atomistic valence-force field approach and calculations based on the effective-mass approximation we investigate the influence of strain effects on the band alignment and general excitonic properties of core/shell CdSe/CdS dot/rod nanoparticles. We find that the inclusion of strain effects leads to an increase in exciton energy as well as to a decrease in electron and hole wave function overlap. Importantly, the native type-I band alignment of the CdSe/CdS material system is preserved and does not change into an quasi-type-II or even type-II band offset for the nanoparticles. Furthermore, we analyze the impact of strain on the spectral diffusion of the fluorescence emission of these nanoparticles, which is explained by migrating surface charges. Our calculations show that the addition of strain effects leads to increased energy shifts as well as larger changes in the squared electron and hole wave function overlap, while the correlation of both also exhibits a steeper slope than for the unstrained system. For a given CdSe core size, an increase in CdS-shell thickness decreases the possible ranges of energy shift and squared wave function overlap without changing the slope of their correlation. On the other hand, for a given nanoparticle overall thickness, dot/rod systems with a small CdSe core exhibit the strongest influenceability by surface charges.

Fluorescence Quantum Yield and Single-Particle Emission of CdSe Dot/CdS Rod Nanocrystals

“…The number of grid points was 35 × 35 × 110. For the calculations of electron wave functions under the influence of a trapped hole, the hole potential, described as a Coulombic charge, was overlayed with the confinement potential of the electron, similar to the implementation of surface charges in refs. , …”

Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution

“…Indeed, spectral diffusion has been reported from single emitters in systems as diverse as diamond vacancies (Figure A), epitaxially grown III–V QDs (Figure B), single organic molecules (Figure C), colloidal II–V QDs (Figure D), and colloidal halide perovskite QDs (Figure E) . For colloidal materials, spectral diffusion has been reported for shapes including nanorods, nanoplatelets, and dot–rod heterostructures . In many of these systems, not only does the instantaneous emission energy change with time but also the intensity (PL quantum yield) varies as well.…”

“…62 For colloidal materials, spectral diffusion has been reported for shapes including nanorods, 233 nanoplatelets, 234 and dot−rod heterostructures. 235 In many of these systems, not only does the instantaneous emission energy change with time but also the intensity (PL quantum yield) varies as well. This intensity variation is known as fluorescence intermittency, 236 blinking, 237 or flickering 238,239 and is often coupled with spectral diffusion as the nonradiative recombination rate and emission energy both fluctuate, sometimes due to related processes, as we discuss below.…”

Design rules for obtaining narrow luminescence from semiconductors made in solution

“…Indeed, spectral diffusion has been reported from single emitters in systems as diverse as diamond vacancies (Figure 14A), 226 epitaxially grown III-V QDs (Figure 14B) 227 , single organic molecules (Figure 14C) 228 , colloidal II-V QDs (Figure 14D) 229 , and colloidal halide perovskite QDs (Figure 14E). 62 For colloidal materials, spectral diffusion has been reported for shapes including nanorods 230 and nanoplatelets 231 and dot-rod heterostructures 232 . In many of these systems, not only does the instantaneous emission energy change with time, but the intensity (PL quantum yield) varies as well.…”