Synthesis and characterization of MnS and MnSe nanoparticles: Morphology, optical and magnetic properties N. Moloto a,⇑ , M.J. Moloto b , M. Kalenga a , S. Govindraju a , M. Airo a a Molecular Science Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa b Department of Chemistry, Vaal University of Technology, Private Bag X021, Vanderbijlpark 1900, South Africa article info Article history: Available online 28 June 2013 Keywords: Chemical synthesis Magnetic properties Optical properties Nanostructures Semiconductors abstract Herein, we report on the synthesis of manganese chalcogenide nanoparticles using mild synthetic meth- ods. The MnS nanoparticles were synthesised using a single-source precursor method with tetramethyl- thiuram disulfide as a ligand, whilst the MnSe nanoparticles were synthesised by reacting reduced elemental selenium with manganese. These synthetic methods resulted in crystalline MnS nanoparticles with wire-like morphology with high aspect ratio and MnSe nanorods that were nearly mono-dispersed. The absorption band-edges of both MnS and MnSe were blue-shifted from the reported bulk band-edges indicative of quantum confinement effects seen in nanoparticles. Furthermore, both MnS and MnSe showed paramagnetic characteristics with the ESR spectra showing broad single resonance peaks with g-values of 2.0064 and 2.0068 respectively. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Semiconductor nanoparticles of manganese chalcogenides have attracted a lot of attention due to their interesting electronic struc- tures and magneto-optical properties. Unlike conventional II–VI semiconductors such as CdS and CdSe, these semiconductors offer additional versatility, i.e. their metal cores are less toxic and their variable oxidation states result in wide range of applications and their magnetic susceptibility offers completely new avenues of applications. Manganese sulfide (MnS) is a wide band gap semi- conductor with a bulk band gap of 3.1 eV. It usually exist in three phases, a green stable a-MnS form (alabandite) with a rock salt (RS) structure, a b-MnS and a c-MnS (both pink) which are both meta-stable modifications with zinc blend (ZB) and wurtzite (W) structures respectively [1–3]. In previous studies considerable ef- fort had been put on controlling the crystalline phases and the morphologies [4–6]. Recently, a variety of novel shapes such as MnS nanorods, hollow spheres, porous networks, coral shaped and floral-like arrangements have been synthesised by different methods such as hydrothermal, solvothermal, microwave irradia- tion, spray pyrolysis and chemical bath deposition [7–10]. These methods usually result in non-reproducible properties of the nanoparticles. Just like manganese sulfide, manganese selenide in bulk form is a wide band gap semiconductor with a band gap of 2.65 eV. It can exist in many forms and possesses optoelectronic, transport and magnetic properties. Traditionally molecular beam epitaxy (MBE), organometallic vapor phase epitaxy (OMVPE) and the reac- tion of the manganese metal with elemental selenium at high tem- peratures in a quartz tube with the existence of I 2 catalyst have been employed to synthesize manganese selenides [11–13]. These synthetic methods require harsh conditions, expensive equipment as well as toxic materials. Recently, Peng and co-workers synthes- ised cubic micro-crystals of MnSe using a less expensive hydro- thermal method but their synthesis employed a rather toxic Na 2 SeO 3 whilst Wu and co-workers reported on MnSe and MnSe 2 nanorods using the same method with Mn(CH 3 COO) 2 4H 2 O, Se and hydrazine hydrate in NaOH to carry-out their reactions [14]. Herein we report on the synthesis of manganese sulfide nanoparti- cles using a single source precursor method that uses mild condi- tions. Similarly, we report on the synthesis of manganese selenide nanoparticles through the reaction of manganese chloride and selenium using sodium borohydride as a reducing agent in metha- nol. We further report on the optical, morphological and magnetic properties of the nanoparticles. 2. Experimental 2.1. Syntheses of MnS nanoparticles 2.1.1. Materials Tetramethylthiuram disulfide (TMTD), hexadecylamine (HDA), trioctylphosphine (TOP), manganese chloride tetrahydrate (MnCl 2- 4H 2 O) and methanol were available commercially. 0925-3467/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optmat.2013.06.023 ⇑ Corresponding author. Tel.: +27 117176774; fax: +27 865228349. E-mail address: Nosipho.Moloto@wits.ac.za (N. Moloto). Optical Materials 36 (2014) 31–35 Contents lists available at SciVerse ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat