Luminescence enhancement of Mn2+-doped ZnS nanoparticles by insertion of Dy3+ ions

This work demonstrates that the insertion of Dy 3+ enhances the photoluminescence (PL) properties of Mn-doped ZnS nanoparticles (NPs). For this purpose, the chemical coprecipitation method was used to synthesize undoped and (Mn, Dy) co-doped ZnS spherical NPs with cubic structure. As a result, the insertion of the doping elements in the as-synthesized ZnS NPs induced an increase in crystallite size. Although annealing treatment at 300 °C promoted an increase in the crystallite size of the undoped ZnS sample, this did not occur with the annealed (Mn, Dy) codoped ZnS samples, due to the growth inhibitory effects of the dopants on the nanoparticle surface. This finding was validated by morphology analysis, which showed that both synthesized and annealed (Mn, Dy) co-doped ZnS nanoparticles exhibited very similar sizes (2 to 4 nm). Overall, Dy 3+ ions in Mn-doped ZnS induced a redshift of the bandgap energy. The PL studies showed that the Mn-doped ZnS NPs, stimulated by a 365 nm light source, exhibited a green emission related to ZnS defect states, and an orange emission originated from the 4 T 1 → 6 A 1 transitions of Mn 2+ . The intensity of these emissions produced by the co-doped samples (Mn, Dy) was much higher since Dy 3+ created additional defect states in ZnS, while acting as a sensitizer by transferring the absorbed energy to the excited states of Mn 2+ .