Adjustment of the band gap energies of biostabilized CdS nanoparticles by application of statistical design of experiments

The colloidal synthesis of US nanoparticles with the biostabilizers cysteine and glutathione, respectively, at pH values ranging from 4 to 10 is described. For the adjustment of their UV/Vis absorption properties and hence their band gap energies, the Statistical Design of Experiments (DoE) was used. This method allows the simultaneous variation of the synthesis parameters in a systematic manner, and thereby synergistic interaction effects can be obtained. The band gap energies of the quantum dots can be tuned from 3.32 to 4.26 eV by varying kind and concentration of stabilizer, pH value, and concentration of sulfide source. The energy position is significantly dependent on the interaction between the pH value and the concentration of the stabilizer, and the effect of high glutathione concentration is opposite at acidic and alkaline conditions thus leading to band Gaps of 4.10 eV at pH = 6 and of 3.64 eV at pH = 10. Examples for the synthesis of semiconductor nanoparticles with predefined spectroscopic properties and preset preparation conditions, e.g., alkaline conditions for the implementation of acid-sensitive dopants, are given.