Full length article Fe induced optical limiting properties of Zn 1x Fe x S nanospheres T.V. Vineeshkumar a , D. Rithesh Raj a , S. Prasanth a , N.V. Unnikrishnan a , V.P. Mahadevan Pillai b , C. Sudarasanakumar a,⇑ a School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam 686560, India b Department of Optoelectronics, University of Kerala, Kariavattom, Thiruvananthapuram, Kerala 695581, India article info Article history: Received 26 March 2017 Received in revised form 11 July 2017 Accepted 7 September 2017 Available online xxxx Keywords: Nanospheres Two photon absorption Hydro-thermal methods Green emission Optical limiting abstract Zn 1x Fe x S (x = 0.00, 0.01, 0.03, 0.05) nanospheres were synthesized by polyethylene glycol assisted hydrothermal method. XRD studies revealed that samples of all concentrations exhibited cubic structure with crystallite grain size 7–9 nm. TEM and SEM show the formation of nanospheres by dense aggrega- tion of smaller particles. Increasing Zn/Fe ratio tune the band gap from 3.4 to 3.2 eV and also quenches the green luminescence. FTIR spectra reveal the presence of capping agent, intensity variation and shift- ing of LO and TO phonon modes confirm the presence of Fe ions. Nonlinear optical properties were mea- sured using open and closed aperture z-scan techniques, employing frequency doubled 532 nm pumping sources which indicated reverse saturable absorption (RSA) process. The nonlinear optical coefficients are obtained by two photon absorption (2PA). Composition dependent nonlinear optical coefficients ‘‘b”, non- linear refractive index, third order susceptibility and optical limiting threshold were estimated. The sam- ple shows good nonlinear absorption and enhancement of optical limiting behavior with increasing Fe volume fraction. Contribution of RSA on optical nonlinearity of Zn 1x Fe x S nanospheres are also investi- gated using three different input energies. Zn 1x Fe x S with comparatively small limiting threshold value is a promising candidate for optical power limiting applications. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction ZnS is a very interesting wide band gap semiconducting mate- rial having direct band gap (3.7 eV) with large binding energy (40 meV) and a small exciton with Bohr radius of 2.5 nm at room temperature [1–3]. When the size of ZnS nanocrystal is reduced below its Bohr excitonic radius, band structure will be modified and all the optoelectronic properties are enhanced. Nanometer scale semiconductor materials with a defined size and shape have attracted much interest due to their unique properties and poten- tial applications in solar cells, light-emitting diodes (LEDs), photo- catalysis, sensors and bio-labels and so on [4–7]. Among the variety of semiconductors, II-VI group inorganic nanocrystals such as ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe and CdTe have attracted great interest of the scientific community because of their excellent electronic, magnetic and optical properties for diverse applications in optoelectronic sensors, displays, electronic devices, laser devices and nonlinear optical devices, etc. Among these semiconducting nanocrystals, ZnS is less toxic with high luminescence efficiency in the ultra violet to blue spectral range, low absorption coefficient, and excellent transparency to infrared. Hence, it is recognized as one of the most promising material for various optoelectronic device applications. ZnS has been targeted as an efficient semiconductor host to dope different metal impurities which in turn enhances the optical, electrical and magnetic properties. The optoelectronic properties can be engineered by controlling the crystallite size and size distri- butions or by doping impurities into the nanocrystals. Doped semi- conductor nanoparticles have been regarded as a new class of materials which have wide range of applications in sensors, dis- plays, electronic devices, laser devices and nonlinear optical devices, etc. Effective interaction between the dopant ion and the host material determines the novel property of the developed material To synthesize ZnS nanocrystals with different morphology, var- ious methods have been employed, including the solvothermal and hydrothermal, the single-source molecular precursor, the chemical vapor deposition (CVD), the liquid–crystal template, and the c-irradiation [8–14]. Among various methods, the hydrothermal method is more promising for the synthesis of crystals due to its low cost, high efficiency and the potential for large scale produc- https://doi.org/10.1016/j.optlastec.2017.09.006 0030-3992/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: vineeshviswan@gmail.com (T.V. Vineeshkumar), c.sudarsan. mgu@gmail.com (C. Sudarasanakumar). Optics and Laser Technology xxx (2017) xxx–xxx Contents lists available at ScienceDirect Optics and Laser Technology journal homepage: www.elsevier.com/locate/optlastec Please cite this article in press as: T.V. Vineeshkumar et al., Fe induced optical limiting properties of Zn 1x Fe x S nanospheres, Opt. Laser Technol. (2017), https://doi.org/10.1016/j.optlastec.2017.09.006