Synthesis and Optical Properties of Mn2+-Doped ZnS Nanoparticles in Solutions and Coatings

Mn2+-doped ZnS nanoparticles with different Mn-doping concentrations stabilized by hydroxypropyl cellulose (HPC) have been synthesized in ethanolic solutions and coatings. Their optical and structural properties have been characterized by means of UV-vis spectroscopy, luminescence spectroscopy, high resolution transmission electron microscopy (HRTEM) and small angle X-ray scattering (SAXS). Solutions and coatings exhibit a strong luminescence at 590 nm when excited with UV light showing that Mn2+ is incorporated into the ZnS nanoparticles. The highest luminescence intensity is obtained with an Mn2+ concentration of 2 mol%. HRTEM and SAXS investigations show that the particles are crystalline and are 3 ± 0.5 nm in size. Irradiation of the coatings with UV light leads to a photochemical oxidation of the particles, as shown by the decreasing absorption of the coating with irradiation time and a blue shift of the absorption maximum. Furthermore, the luminescence intensity first strongly increases and then decreases completely with UV-irradiation time. Both phenomena can be explained by the photochemical oxidation of the particles.