ABSTRACT
Ternary metal chalcogenide nanocrystals (NCs) offer exciting opportunities as novel materials to be explored on the nanoscale showing optoelectronic properties tunable with size and composition. CuInS2 (CIS) NCs are the most widely studied representatives of this family as they can be easily prepared with good size control and in high yield by reacting the metal precursors (copper iodide and indium acetate) in dodecanethiol (DDT). Despite the widespread use of this synthesis method, both the reaction mechanism and the surface state of the obtained NCs remain elusive. Here, we perform in situ X-ray diffraction using synchrotron radiation to monitor the pre- and postnucleation stages of the formation of CIS NCs. SAXS measurements show that the reaction intermediate formed at 100 °C presents a periodic lamellar structure with a characteristic spacing of 34.9 Å. WAXS measurements performed after nucleation of the CIS NCs at 230 °C demonstrate that their growth kinetics depend on the degree of precursor conversion achieved in the initial stage at 100 °C. NC formation requires the cleavage of S-C bonds. We reveal by means of combined 1D and 2D proton and carbon NMR analyses that the generated dodecyl radicals lead to the formation of a new thioether species R-S-R. The latter is part of a ligand double layer, which consists of dynamically bound dodecanethiolate ligands as well as of head-to-tail bound R-S-R molecules. This ligand double layer and a high ligand density (3.6 DDT molecules per nm2) are at the origin of the apparent difficulty to functionalize the surface of CIS NCs obtained with the DDT method.
ABSTRACT
Chemically synthesised In(Zn)P alloy nanocrystals are doped with Eu(3+) ions using europium oleate as a molecular precursor and are subsequently covered with a ZnS shell. The presence of zinc in the synthesis of the InP core nanocrystals leads to the formation of an In(Zn)P alloy structure, making it possible to obtain stable fluorescence emission at 485 nm. We demonstrate by means of steady state and time resolved photoluminescence measurements that resonant energy transfer takes place from the In(Zn)P/ZnS host to the Eu(3+) dopant ions. It results in the characteristic phosphorescence lines of Eu(3+) originating from the transitions between the lowest-lying excited state (5)D0 to the (7)F(J) (J = 1, 2, 3, 4) ground states. The maximum phosphorescence efficiency is obtained for an initially applied Eu(3+) : In(3+) molar ratio of 0.3 : 1, resulting in a final doping level of approximately 4%.
