Dynamics of the Size Distribution of CdTe Quantum Dot Ensembles during Growth in Liquid and Crystalline Phases

Abstract

We recently reported that the growth rate of colloidal CdTe nanoparticles decreases by orders of magnitude when the particles undergo a phase transition from liquid to crystal. The dynamics of nanoparticle growth are dominated by this factor rather than the size dependence of the chemical potential. Herein we discuss how the phase transition affects the size distribution and photoluminescence quantum efficiency of the nanoparticles. We suggest that the absorption linewidth is a better monitor of size distribution than the photoluminescence linewidth because the photoluminescence quantum efficiency, which affects the latter via energy transfer, varies substantially with reaction time. We find that the size distribution broadens in the early stages of growth possibly because of inhomogeneities in the phase transition radius or because particles nucleated at later times coalesce with nanocrystals. The quantum efficiency is enhanced when tellurium is depleted in the reaction solution, giving a cadmium-enriched surface. Batches with high initial tellurium and cadmium concentrations show a substantial amount of delayed nucleation, lower quantum efficiency and some anisotropic growth.

Preparation of Highly Luminescent CdTe/CdS Core/Shell Quantum Dots

“…Due to their size-dependent PL, which is tunable across the visible spectrum, CdTe QDs are one of the most studied semiconductor materials. [6][7][8][9][10][11][12][13] Hindering the full practical application of CdTe QDs-either as labels or in devices-is their known inherent chemical instability, which is due to the oxidation of Te and is especially observed in the case of oilsoluble CdTe QDs, usually prepared via the organometallic hotinjection route in organic media. [14][15][16][17] The as-prepared oil-soluble CdTe QDs exhibit a spontaneous and irreversible PL peak blue-shifting (i.e.…”