Multicolor Luminescence from Transition Metal Ion (Mn²⁺ and Cu²⁺) Doped ZnS Nanoparticles

Mn and Cu doped ZnS nanoparticles in powder form were prepared by a simple solvothermal route. Particle size and crystal structure of the products were investigated through X-ray diffraction study revealing the formation of cubic ZnS nanoparticles of average diameter 2.5 nm. Particle size was also verified by the high resolution transmission electron microscopic images. Blue emission at ∼445 nm was observed from the undoped sample, which was attributed to the presence of large surface defects. With increasing doping concentration the defect related emission gradually quenches and subsequently the impurity related emissions appeared. Mn doped samples exhibited orange emission at ∼580 nm which may be attributed to the transition between ⁴T₁ and ⁶A₁ energy levels of the Mn²⁺ 3d states. Whereas, the Cu doped ZnS nanoparticles exhibited a red shifted strong blue emission at ∼466 nm which is attributed to the transition of the electrons from the surface states to the 't ₂' levels of Cu impurities.