The effect of Co 2+ and Co 3+ on photoluminescence characteristics of ZnS nanocrystallines

Abstract

Free-standing powder of doped ZnS nanoparticles has been synthesized by using a chemical co-precipitation of Zn 2+, Co 2+, Co 3+ with sulfur ions in aqueous solution. X-ray diffraction analysis shows that the diameter of the particles is ∼2.6±0.2 nm. Unique luminescent properties have been observed from ZnS nanoparticles doped with Co 2+ and Co 3+. The effect of Co 3+ on emission spectra of doped samples is remarkably different from that of Co 2+. Very strong and stable visible-light emission have been observed from ZnS nanoparticles doped with Co 2+. However, the fluorescence intensity of Co 3+-doped ZnS nanoparticles is much weaker than that of ZnS nanoparticles. Nanoparticles can be doped with cobalt during the synthesis without altering the X-ray diffraction pattern and emission wavelength. However, doping makes the fluorescence intensity vary. The fluorescence intensity of doped sample is about five times of that of pure ZnS nanocrystallines when the doped mole ratio of Co 2+ is 0.5%. The fluorescence efficiencies of samples decreases as doped mole ratio of Co 2+ and Co 3+ increases. When Co 3+ is doped in ZnS nanoparticles, the fluorescence efficiencies of doped ZnS nanoparticles almost died away. Therefore, Co 3+ leads to fluorescence decay of ZnS nanocrystallites.