The effect of ultraviolet irradiation on the optical properties of ZnS: Mn synthesized by hydrothermal method and using thioglycolic acid

ZnS:Mn nanoparticles (C_Mn = 15 mol%) were synthesized from thioglycolic acid HSCH₂COOH (TGA) and initial chemicals Zn(CH₃COO)₂.2H₂O, Mn(CH₃COO)₂.4H₂O by the hydrothermal method at 220 °C for 5h and 20 h. The XRD patterns show that nanoparticles possess a hexagonal wurtzite crystalline structure with size about of 10-20 nm. Due to TGA creating a S^2- source, the hydroxyl groups of a-hydroxyl acetic acid (glycolic acid) molecules with electron pairs can be coordinated with vacancy 3d (t_2g) orbitale of Zn²⁺, Mn²⁺ ions and to form surface passive shells of ZnS and ZnS:Mn. The effect of ultraviolet (UV) irradiation on the photoluminescence (PL) spectra of coated ZnS, ZnS:Mn nanoparticles also was investigated by UV wavelength of 337 nm. The results show that the yellow-orange band intensity increases with increasing UV irradiation time, but their PL peak position unchanged. These results can be explained by the energy transition process, polymerization, photochemical process and gradual diffusion of Mn²⁺ into a ZnS crystal network due to the activity of this UV irradiation.