The growth of Co:ZnO/ZnO core/shell colloidal quantum dots: changes in nanocrystal size, concentration and dopant coordination.
We report a synthesis route for the growth of Co:ZnO/ZnO core/shell quantum dots. This procedure consists of successive steps, comprising the addition of diluted precursor salt solutions, and heat treatment at 50 degrees C. By deriving a relation between the extinction coefficient at 250 nm and the nanocrystal diameter, we are able to monitor changes in quantum dot concentration during shell growth. We found that a mechanism based on the nucleation of new particles after salt addition and subsequent Ostwald ripening during the heat treatment is responsible for the shell growth. Based on ligand-field absorption spectroscopy, we demonstrate that the Co(2+) ions adsorbed at the surface of Co:ZnO quantum dots are incorporated inside the ZnO shells. Finally, EPR spectroscopy indicates that the surface-adsorbed Co(2+) ions can be incorporated as substitutional as well as interstitial Co(2+) ions.
Lommens
Petra
P
Physics and Chemistry of Nanostructures, Ghent University, Krijgslaan 281-S12, 9000 Ghent, Belgium.
Lambert
Karel
K
Loncke
Frank
F
De Muynck
David
D
Balkan
Timuçin
T
Vanhaecke
Frank
F
Vrielinck
Henk
H
Callens
Freddy
F
Hens
Zeger
Z
D003035:Cobalt / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D045663:Quantum Dots; D013499:Surface Properties; D015034:Zinc Oxide / Q000138:chemical synthesis* / Q000737:chemistry*
D003102:Colloids; D003035:Cobalt; D015034:Zinc Oxide