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

• Published in: Chemphyschem 2008-05, Vol.9 (7), p.1057-1061
• Main Authors: Piepenbrock, Marc-Oliver M., Stirner, Tom, O'Neill, Mary, Kelly, Stephen M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cadmium - chemistry; colloids; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystallization; Electronics; Exact sciences and technology; growth factors; Kinetics; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Luminescence; Materials science; Molecular electronics, nanoelectronics; Nanocrystalline materials; nanoparticles; Nanoscale materials and structures: fabrication and characterization; Particle Size; Phase Transition; Photochemistry; photoluminescence; Physics; Quantum Dots; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surface Properties; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Tellurium - chemistry
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200800025

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. Influential phase transition: The liquid–solid phase transition drastically alters the growth rate of colloidal CdTe nanoparticles (see figure). The energy distribution and photoluminescence quantum efficiency of the nanoparticles also depend on the particle phase at the growth temperature.