Please cite this article in press as: S.K. Mehta, S. Kumar, Photoactivation and perturbation of photoluminescent properties of aqueous ZnS nanoparticles: Probing the surfactant-semiconductor interfaces. Mater. Chem. Phys. (2011), doi:10.1016/j.matchemphys.2011.07.059 ARTICLE IN PRESS G Model MAC-15077; No. of Pages 8 Materials Chemistry and Physics xxx (2011) xxx–xxx Contents lists available at ScienceDirect Materials Chemistry and Physics j ourna l ho me pag e: www.elsevier.com/locate/matchemphys Photoactivation and perturbation of photoluminescent properties of aqueous ZnS nanoparticles: Probing the surfactant-semiconductor interfaces S.K. Mehta a,∗ , Sanjay Kumar b a Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh 160014, India b Department of Chemistry, Government College, Chowari, Chamba, H.P. 176302, India a r t i c l e i n f o Article history: Received 17 February 2011 Received in revised form 15 July 2011 Accepted 24 July 2011 Keywords: ZnS NPs Nucleation Photoluminescence spectroscopy Surfactants Interfaces Surface passivation a b s t r a c t The in situ photochemistry of aqueous colloidal ZnS has been studied in relation to variety of the sur- factants as surface passivating agents. The photoluminescence (PL) intensity of ZnS nanoparticles (NPs) has been drastically enhanced as compared to their bare counterparts due to surface passivation by surfactants depending upon their molecular structure. Cationic surfactants of alkyltrimethylammonium bromide series with different chain lengths (C 16 , C 14 and C 12 ) have been tested. The PL emission of ZnS NPs decreases with decrease in chain length because of ineffective stabilization and passivation of surface because the larger sized NPs were produced in the surfactant with smaller chain length. On the other hand, three anionic surfactants with C 12 chain length with different head groups have been capable of comparatively effective passivation to produce stable NPs with better luminescence. The changing nature of surface states during growth and long time ripening of ZnS NPs has also been monitored by comparing time evolution PL emission in different surfactants. The influence of UV-light irradiation in enhancing the PL emission has been found to be surfactant structure dependent with maximum enhancement observed with the surfactants having -electrons in their head group functionalities. The anionic surfactants also display better tendency to retain the enhanced PL of ZnS NPs for longer time durations. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Recently, there is increasing interest in chalcogenides nanos- tructures in view of their optoelectronic properties that leads to extensive applications in optical devices [1–4]. II–VI semiconduc- tors based on Zinc chalcogenides are the front-runners for such applications because of their intense absorption, high quantum yield and, more importantly, photoluminescence (PL) properties that are size-dependent and hence tunable over a wide wavelength range. However, the major problem with semiconductor nanopar- ticles (NPs) is related to their surface electronic states that lie within HOMO-LUMO gap and provide non-radiative decay chan- nels mainly during agglomeration leading to a severe degradation in optoelectronic properties. Applying suitable protective cover- ings of specific materials during their synthesis can serve two fold motives i.e. tuning the optoelectronic properties and acting as stabilizing agent to prevent the unlimited growth. During the syn- thesis of aqueous ZnS NPs dispersion, the most challenging aspect is to explore the efficiency of variety of organic molecules that can provide suitable surface functionalities and make the NPs compati- ble with biological systems. In this context, the methods that make ∗ Corresponding author. Tel.: +91 172 2534423; fax: +91 172 2545074. E-mail address: skmehta@pu.ac.in (S.K. Mehta). the use of surfactants have attracted considerable interest where size and surface states of the NPs have been controlled by adsorbing long-chain surfactant molecules/aggregates onto the ZnS surface, forming nearly bilayer/vesicles like structures thereby mimic the biological systems [5,6]. To fully exploit the application potential of semiconductor NPs, further elaborations are necessary to estab- lish the additional role played by surfactants as stabilizing agents in modification and creation of surface recombination centers which can significantly change the optical and PL properties. While the adsorption of various organic or inorganic layers appear to influ- ence only mildly the absorption characteristics of semiconductor NPs, the PL emission efficiency has been strongly affected. So far, only few systematic reports [7–9] has been developed for general understanding about the ever changing PL behavior of ZnS NPs due to passivation of surface states arising from surface nonstoichiom- etry, unsaturated bonds, vacancies, interstitial atoms and atoms at surfaces and grain boundaries etc. Tang et al. [10] have estab- lished the origin of discrete energy levels of lattice point defects and surface states by comparing the PL properties of ZnS/AOT and ZnS/pyridine/AOT systems. In addition, the adsorbing molecules can interact with semiconductor surface to form weak charge- transfer complex by acting as adsorbing lewis acids or base accord- ing to their chemical structure thereby alter the PL intensity [11,12]. Therefore, the possibilities of surfactants with different electronic arrangements and charges on their head group functionalities to 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.07.059