Synthesis of cadmium sulfide Q particles in water-in-CO2 microemulsions

Semiconductor nanoparticles of cadmium sulfide were synthesized in ammonium perfluoropolyether (PFPE-NH4) stabilized water-in-CO2 microemulsions. The particle size was tuned by varying the water-to-surfactant molar ratio (w(o )): w(o) ratios of 5 and 10 yielded nanocrystals with exciton energies of 3 .86 and 3.09 eV, corresponding to mean particle radii of 0.9 and 1.8 nm, re spectively. These exciton energies are significantly higher than the bulk b and gap energy for CdS (2.45 eV) due to quantum confinement effects. Effect ively, w(o) controls the size of the compartmentalized water droplets in wh ich the particles grow.