Synthesis, characterization and optical properties of water-soluble ZnS:Mn2+ nanoparticles

ZnS nanoparticles with Mn2+ doping (0.5-20%) have been prepared through a simple chemical method, namely the chemical precipitation method. The structure of the nanoparticles has been analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV-vis spectrometer. The size of the particles is found to be 3-5 nm range. Photoluminescence spectra were recorded for undoped ZnS nanoparticles using an excitation wavelength of 320 nm, exhibiting an emission peak centered at around 445 nm. However, from the Mn2+-doped samples, a yellow-orange emission from the Mn2+4T1-6A1 transition is observed along with the blue emission. The prepared Mn2+-doped sample shows efficient emission of yellow-orange light with the peak emission 580 nm with the blue emission suppressed. The maximum PL intensity is observed only at the excitation energy of 3.88 eV (320 nm). Increase in stabilizing time up to 48 h in de-ionized water yields the enhancement of emission intensity of doped (4% Mn2+) ZnS. The correlation made through the concentration of Mn2+ versus PL intensity resulted in opposite trend (mirror image) of blue and yellow emissions.