2-1. Syntheses of the cysteamine-capped ZnS:Mn nanocrystals
All the solvents, except deionized (DI) water, were purchased from Sigma-Aldrich (reagent grade) and distilled prior to use. All the reactants, including cysteamine (HSCH2CH2NH2), ZnSO4, MnSO4, and Na2S, were purchased from Sigma-Aldrich and used as received. A solution of quinine sulfate in H2SO4 (0.1 M) was purchased from Fluka to evaluate the relative quantum efficiencies of the products.
ZnS:Mn-Cyst nanocrystals were synthesized following slight modifications of a previously reported method for the synthesis of conventional L-aminoacids-capped ZnS:Mn nanocrystals via the formation of zinc (II)-amino acid coordinated complexes as reactive intermediates.16 A 50 mL aqueous solution of ZnSO4·5H2O (1.44 g, 5 mmol) was slowly added to a 50 mL aqueous solution containing 0.77 g (10 mmol) of cysteamine. MnSO4·H2O (0.04 g, 0.2 mmol) and Na2S (0.40 g, 5 mmol) were seperatley dissolved in 20 mL of DI water. This mixture was subsequently transferred to the flask containing the [Zn-Cyst] complexes under vigorous stirring. The pH of the solutions was adjusted by the addition of 0.1 M NaOH or 0.1 M H2SO4 aqueous solution to the mixture solution. The resulting solution was refluxed for ∼10 h. Slow cooling to ambient temperature and the addition of ethanol produced yellow-white precipitates at the bottom of the flask. Finally, the obtained solids were separated by centrifugation and decanting the supernatant. The solids were