Synthesis and optical properties of undoped and Eu-doped ZnS nanoparticles

Pure and europium (Eu)-doped zinc sulfide (ZnS) nanoparticles were synthesized by the solvothermal method and characterized by powder x-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and photoluminescence (PL). The XRD pattern showed that as-prepared samples are a mixture of complex chemical groups. Heat treatment of the samples at 300 °C showed a phase transformation of the complex chemical mixture to the ZnS state. The crystallite size of undoped ZnS was found to be ∼23 nm. However, ZnS:Eu nanoparticles showed a crystallite size of ∼28 nm. The lattice constant of undoped ZnS was found to be 5.382 A and that of Eu-doped ZnS was 5.34 A. Further heating the samples to 500 °C showed a phase transition to the ZnO state. The SEM studies revealed that ZnS nanoparticles are agglomerated, crispy and porous. The FTIR spectrum showed the presence of hydroxyl groups in the sample. The PL studies showed a shift in the emission peak from 390 to 420 nm upon heating the samples from 300 to 500 °C.