Optical Dispersion, Permittivity Spectrum and Thermal-Lensing Effect in Nickel-Doped Zinc Sulfide Nanoparticles F. ABBASI, 1 E. KOUSHKI, 2,4 M.H. MAJLES ARA, 1 and R. SAHRAEI 3 1.—Faculty of Physics, Kharazmi University, Tehran, Iran. 2.—Department of Physics, Hakim Sabzevari University, Sabzevar, Iran. 3.—Department of Chemistry, University of Ilam, Ilam, Iran. 4.—e-mail: ehsan.koushki@yahoo.com In this paper, Ni-doped ZnS (ZnS:Ni 2+ ) nanoparticles (NPs) have been pre- pared through a chemical method. The average size of the particle is 45 nm. Thin films of the particles have been prepared by using the spin-coating method. The linear and nonlinear optical properties of Ni-doped ZnS thin films and the colloidal solution of them have been studied widely. Using a precise numerical method, the refractive index curve (dispersion curve), absorption coefficient and optical permittivity of Ni-doped ZnS film have been obtained. Using these values, the absorption coefficient of the colloidal solution of Ni- doped ZnS particles has been simulated and compared with experimental results. Finally, using the z-scan method at low laser irradiation, the thermo- optical effect has been studied and the nonlinear refractive index due to this effect has been reported. Key words: Ni-doped ZnS (zinc sulfide) nanoparticles, optical properties, nanocolloid, nanostructured thin film, z-scan INTRODUCTION Recently, semiconductor nanoparticles (NPs) have been receiving much interest due to their unique optical and electronic properties and poten- tial applications in optoelectronic devices. 1,2 Zinc sulfide belongs to II–VI compound semiconductors with a wide band gap of 3.5–3.8 eV (at room temperature), which has various applications such as electroluminescence, field effect transistors, field emitters, light-emitting diodes (LEDs), infrared windows, dielectric filters, reflectors and photo electrochemical cells. 3–6 Two allotropes of ZnS are commo: zinc blende and hexagonal wurtzite; how- ever, the first phase is more stable iatn room temperature. 7 Due to nontoxicity and compatibility with the environment, ZnS is distinguished from the other members of II–VI compound semiconductors. 8 ZnS is a host, and doping with transition metal ions can improves the physical properties and provide the potential for many applications, including biological detection, optoelectronic devices, phosphors, LEDs, buffer layers in Cu(In,Ga)Se2 (CIGS)-based thin film solar cells, lasers, etc. 9–12 Hence, the synthesis and investigation of transition metal ion-doped ZnS nanostructures has been widely studied. 13–16 Fur- thermore, Ni-doped ZnS nanostructures have been the focus of attention in the studies of luminescence and photocatalystic and magnetic properties. 17–23 Molaei reported a new thermochemical synthesis for Ni-doped ZnS nanocrystals and investigated their photoluminescence properties. 24 Kudo and Sek- izawa 25 reported Ni-doped ZnS as a visible-light- driven photocatalyst for hydrogen evaluation from aqueous solutions. Shah et al. 23 evaluated Ni-doped ZnS NPs as a photocatalyst for the removal of the color of aqueous solutions of rhodamine B (RhB) dye and Sahraei and Darafarin 26 prepared nanocrys- talline Ni-doped ZnS thin films by the chemical bath deposition method in a weak acidic solution con- taining ethylenediamine tetra-acetic acid disodium salt (Na 2 EDTA) as a complexing agent. In the present work, details of the synthesis of Ni-doped ZnS NPs have been presented. After (Received October 1, 2016; accepted July 4, 2017) Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-017-5678-3 Ó 2017 The Minerals, Metals & Materials Society