Colloidal CdSe nanocrystals from tri-n-octylphosphine: Part II: control of growth rate for high quality and large-scale production by tuning Cd-to-Se stoichiometry.
Colloidal CdSe nanocrystals were synthesized in reaction media consisting of tri-n-octylphosphine (TOP) without addition of other species; the single-step approach used cadmium oxide (CdO) and TOPSe as Cd and Se sources, respectively. The temporal evolution of the optical properties of the growing TOP-capped CdSe nanocrystals was monitored for a couple of hours, showing that there are two distinguishable stages of growth: an early stage (less than 5 minutes) and a later stage; the growth kinetics of the two stages is a function of the Cd-to-Se precursor molar ratios. A rational choice of 2-6Cd-to-1Se molar ratio was found, based on the temporal evolution of the photoluminescent (PL) efficiency (studied as PL intensity and sensitivity to the media of dispersion, and non-resonant Stokes shifts). For a 2Cd-to-1Se synthesis, the growth in size was slow in the early stages and became fast in the later stages; this fast-later-stage feature could be suppressed by going to a synthesis with a 4-6Cd-to-1Se mole ratio: the nanocrystals between 0.5-60 min growth time exhibit very much similar optical properties, with less than 19 nm redshift of bandgap absorption and emission occurring. Thus, the synthetic route developed here, with a rational 4-6Cd-to-1Se molar ratio, enables us to produce high-quality CdSe nanocrystals on a large-scale with a high degree of synthetic reproducibility. The insights gained facilitate a deeper understanding of the concept of what constitutes high-quality nano-crystals: high PL efficiency resulting from a low growth rate, which can be thoroughly and readily investigated by the red-shift rate of the band-gap peak positions; in addition, the insights gained help us to define a proper synthetic approach for large-scale production with high-quality product.
Yu
Kui
K
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario KIA OR6, Canada.
Zaman
Badruz
B
Ripmeester
John A
JA
D002104:Cadmium / Q000737:chemistry*; D019187:Cadmium Compounds / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry*; D005663:Furans / Q000737:chemistry; D006586:Hexanes / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D046529:Microscopy, Electron, Transmission; D036103:Nanotechnology / Q000379:methods*; D009943:Organophosphorus Compounds / Q000737:chemistry; D010087:Oxides / Q000737:chemistry; D012643:Selenium / Q000737:chemistry*; D018036:Selenium Compounds / Q000737:chemistry*; D012666:Semiconductors; D012997:Solvents; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D014466:Ultraviolet Rays
D019187:Cadmium Compounds; D003102:Colloids; D005663:Furans; D006586:Hexanes; D008024:Ligands; D009943:Organophosphorus Compounds; D010087:Oxides; D018036:Selenium Compounds; D012997:Solvents; D002104:Cadmium; C029663:cadmium oxide; C018674:tetrahydrofuran; C044965:trioctyl phosphine oxide; C058667:cadmium selenide; D012643:Selenium