Cadmium sulfide nanoparticles with a hexagonal phase ( 10 nm) were prepared at a relatively low temperature (70 C). This synthesis was carried out shortly (30 min) through a new micro-emulsion (O/W) induced by ultrasound without surfactant. Ultrasound can provide an excess energy for new interface formation and obtain emulsions even in the absence of surfactants. This technique avoids some problems that normally exist in conventional micro-emulsion synthesis such as the presence of different additives and calcinations. In addition, it was possible to tune the particle size, the band gap, and the phases of CdS nanoparticles by changing the variables such as ultrasonic irradiation time, intensity, precursor, and ratio of the components. It was also found that the synthesized nanoparticles have a bandedge emission at about 460 nm with a blue-shift to a higher energy which is due to the typical quantum confinement effects. The product was characterized by different techniques such as UV–visible absorption spectroscopy, X-ray powder diffraction, and high resolution transmission electron microscopy (HRTEM).

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