Elsevier

Materials Discovery

Volume 12, June 2018, Pages 1-8
Materials Discovery

Microwave-assisted synthesis, characterization and photoluminescence interaction studies of undoped, Zr2+, Rh3+ and Pd2+ doped ZnS quantum dots

https://doi.org/10.1016/j.md.2018.08.001Get rights and content

Abstract

Here, we report the simple and low-cost synthesis of undoped, Zr2+, Rh3+ and Pd2+ doped ZnS quantum dots (QDs) by a microwave-assisted method. We study the compositional, structural, and optical properties by XRD, SEM-EDX, TEM, FTIR, UV–vis and PL spectroscopy. The quantum confinement effect of the products was confirmed by means of spectroscopic measurements. XRD and TEM show that the synthesized ZnS quantum dots have cubic structures with a diameter of about less than 10 nm. The fluorescence interaction studies suggest that L-Cysteine was effectively quenched the fluorescence intensity of ZnS QDs and form stable Cys-ZnS complex using fluorescence spectroscopy.

Introduction

Semiconductor nanoparticles have attracted widespread attention because of their unique optical and electrical properties suitable for applications in gas sensors, ultraviolet detectors, photoelectric devices, photocatalysis and luminescence properties [[1], [2], [3], [4], [5], [6]]. Recently extensive efforts have been devoted towards the synthesis and characterization of metal doped chalcogenide nanoparticles. The nano-sized chalcogenides exhibit excellent electrical, optical and magnetic properties compared to that of bulk material due to quantum confinement and surface effects. In order to get enhanced emissions of luminescent materials with various wavelengths, it is important to synthesize ions doped semiconductor nanoparticles. Recently, ions doped semiconductor nanoparticles with applications in sensors, solar cells, photocatalysts and light emitting diodes, have been attracting special attention [[2], [3], [4], [5], [6], [7]]. The interesting, unique physical properties and strong application potential of some wide band gap IIsingle bondVI compound semiconductors have received considerable attention among researchers [[8], [9], [10], [11], [12]].

Among the family of IIsingle bondVI semiconductor compounds, ZnS has been realized to be the potential material for extensive research, possible applications in magneto-optical devices and the potential generation of results to other candidates because of its wide band gap (3.54 eV), large exciton binding energy (40 meV), and high index of refraction (2.27 at 1 μm). ZnS with cubic zinc blende and hexagonal wurtzite crystal structure has band gap energies of ∼3.72 and ∼3.77 eV at room temperature, respectively [13,14]. Particularly, this makes it convenient for use as a host lattice for a large variety of dopants. Therefore, during the last several decades, there are many studies on IIsingle bondVI semiconductor nanoparticles doped with different metal ions. Up to date, ZnS has been investigated as a matrix to synthesize doping nanostructures for enhanced optical properties. Among them, Cu2+ [15], Ag+ [16], Au3+ [16], Mn2+ [15,17], Fe3+ [18], Ni2+ [18], Mg2+ [19], Pb2+ [20], Gd3+ [21], Cd2+ [22], La3+ [23], Eu3+/2+ [24,25], Dy3+ [26], Sn2+ [27], Nd2+ [28], Co2+ [18,29], Cr2+ [30] and Ru3+ [31] ions-doped ZnS nanostructures have been obtained. From this point of view, we emphasize a microwave-assisted method to prepare Zr2+, Rh3+ and Pd2+ doped ZnS QDs and to investigate the optimized conditions for their photoluminescence emission and quenching properties.

ZnS nanoparticles with different structures and morphologies including nanotubes, nanosheets and nanowires have been successfully synthesized and studied using a variety of methods. A number of synthesis methods are available for the preparation of ultrafine metal doped ZnS NPs such as sol-gel, hydrothermal, microwave, solid state techniques and spray pyrolysis methods etc. [6,14,[32], [33], [34]]. Among all these methods the preparation of ZnS NPs via a microwave-assisted chemical route has received great attention because it provides favorable factors such as large-scale production, high yield with low cost, high reaction rate, and rapid and homogeneous heating compared to a conventional chemical route which are key parameters to design required tunable properties. The conventional heating sources are very slow to heat the reaction mixture, and also there is a possibility of decomposition of the material at the hot surface of the reaction vessel. The approach utilized in the present work is based on microwave synthesis of nanoparticles from metal salts in solutions. Microwave irradiation (MWI) has several advantages over conventional methods, which include short reaction times, small particle sizes, narrow size distribution and high purity [35].

Semiconductor materials show unusual luminescence properties induced by the quantum size effect. Efforts have been made in realizing luminescence tuneable materials simply by changing the particle size and size distribution and great progress have been achieved [36]. These materials not only give luminescence in various regions but also can add to the excellent properties of ZnS QDs. Optical properties can be altered through doping [37] and ZnS doped with transition metal ion alters the optical and luminescence properties which lead to emission in visible region [38]. In doped ZnS QDs, impurity ions occupy the ZnS lattice site and behave as a trap site for electrons and holes. The electrons are excited from the ZnS valence band to conduction band by absorbing energy equal to or greater than the band gap energy. Subsequent relaxation of these photoexcited electrons to some surface states or levels is followed by radiative decay, enabling luminescence in the visible region. The combination of many desired properties in one material drives great interest to carry out research on doped ZnS QDs.

In this paper, we report the successful synthesis of cubic ZnS QDs and ZnS QDs doped with Zr2+, Rh3+ and Pd2+, having average grain size of less than 10 nm, by the microwave-assisted method to study the effect of dopant on structural, surface and optical properties of ZnS QDs without capping agent. The absorption edges of doped ZnS QDs were blue shifted with respect to the undoped ZnS QDs. The band gap values of doped and undoped ZnS QDs were determined from UV–vis spectroscopy and PL emission spectroscopy. A rapid luminescence quenching with increasing Cys concentration was observed. The binding parameters were determined by Stern-Volmer relation.

Section snippets

Materials and methods

All the chemicals used for synthesis were of AR grade, purchased from Sigma Aldrich chemicals, and for spectral analysis, spectral grade solvents were used. Double distilled water was used for preparing the solutions.

Synthesis of undoped, Zr2+, Rh3+ and Pd2+ doped ZnS QDs

In a typical experiment, for preparing Zr2+, Rh3+ and Pd2+ doped ZnS QDs, 25 ml of 0.1 M zinc acetate and an equal quantity of 0.1 M sodium sulfide were dissolved separately in double distilled water. The solutions were stirred for 30 min using a magnetic stirrer. In a separate

UV–vis absorption analysis

The UV–vis absorption spectra of undoped, Zr2+, Rh3+ and Pd2+ doped ZnS QDs by the microwave-assisted method are shown in Fig. 1. The effects of Zr2+, Rh3+ and Pd2+ dopants on the UV–vis absorption spectrum of ZnS QDs were studied. An absorption edge around 320–340 nm (Zr2+, Rh3+ and Pd2+ doped ZnS QDs) and 370 nm (undoped ZnS QDs) was observed, which does not appreciably change with the variation of the dopants. The calculated band gap values of Zr2+, Rh3+ and Pd2+ doped and undoped ZnS QDs

Conclusions

In this paper, we describe a simple microwave-assisted method to fabricate and stabilize undoped and Zr2+, Rh3+ and Pd2+ doped ZnS QDs without using any capping agent. TEM analysis showed that the synthesized NPs were less than 10 nm in size. The cubic phase of synthesized undoped and doped ZnS QDs was observed from the XRD. The optical properties of the undoped and doped ZnS QDs were investigated by UV–vis and PL spectroscopy. The obtained undoped and doped ZnS QDs showed a band gap of

Financial support

No financial support was provided to any of the authors in the creation/writing of this manuscript.

Conflict of interest

The authors declare that they have no competing interests.

Acknowledgments

The authors would like to acknowledge the Head, Department of Chemistry, Osmania University for providing the necessary facilities. One of the authors, D. Ayodhya wishes to thank the UGC, New Delhi for the award of SRF which supported this work. The authors would like to thank DST–FIST, New Delhi, India for providing necessary analytical facilities in the department.

References (46)

  • P. Yang et al.

    Photoluminescence properties of ZnS nanoparticles co-doped with Pb2+ and Cu2+

    Chem. Phys. Lett.

    (2001)
  • G. Murugadoss

    Luminescence properties of co-doped ZnS: Ni, Mn and ZnS: Cu, Cd nanoparticles

    J. Lumin.

    (2012)
  • B. Poornaprakash et al.

    Achieving room temperature ferromagnetism in ZnS nanoparticles via Eu3+ doping

    Mater. Lett.

    (2016)
  • B. Poornaprakash et al.

    Chemical synthesis, compositional, morphological, structural, optical and magnetic properties of Zn1-x DyxS nanoparticles

    Ceram. Int.

    (2016)
  • K.C. Kumar et al.

    Structural, optical and magnetic properties of Sn doped ZnS nanopowders prepared by solid state reaction

    Physica B: Condens. Matter

    (2017)
  • B. Poornaprakash et al.

    Room temperature ferromagnetism in Nd doped ZnS diluted magnetic semiconductor nanoparticles

    Mater. Lett.

    (2016)
  • L. Liu et al.

    Optical properties of water-soluble Co2+:ZnS semiconductor nanocrystals synthesized by a hydrothermal process

    Mater. Lett.

    (2012)
  • R. Sahraei et al.

    Synthesis and photoluminescence properties of Ru-doped ZnS quantum dots

    J. Lumin.

    (2017)
  • T. Tsuzuki et al.

    Mechanochemical synthesis of metal sulphide nanoparticles

    Nanostructured Mater.

    (1999)
  • J. Mu et al.

    Effect of annealing on the structural and optical properties of non-coated and silica-coated ZnS: Mn nanoparticles

    Mater. Res. Bull.

    (2005)
  • R. Sarkar et al.

    Enhanced visible light emission from Co2+ doped ZnS nanoparticles

    Physica B Condens. Matter

    (2009)
  • K. Muraleedharan et al.

    Green synthesis of pure and doped semiconductor nanoparticles of ZnS and CdS

    Trans. Nonferrous Met. Soc. China

    (2015)
  • S. Kumar et al.

    Room temperature ferromagnetism in Ni doped ZnS nanoparticles

    J. Alloys

    (2013)
  • Cited by (8)

    • Microwave-assisted synthesis of quantum dots

      2022, Quantum Dots: Fundamentals, Synthesis and Applications
    • ZnS-based quantum dots as photocatalysts for water purification

      2021, Journal of Water Process Engineering
      Citation Excerpt :

      The bandgap values of doped and undoped ZnS QDs were calculated 3.88–4.2 eV which is greater than the bulk ZnS (3.3 eV). A blue shift in absorbance was mainly due to the decreased size of ZnS QDs, irrespective of the type of dopant ions [71]. The greener synthesis technique is simple, cost-effective, relatively reproducible, and often results in more stable nanoparticles [72]; there is no requirement for high pressure, energy, temperature, or toxic chemicals.

    • Characterization, luminescence and dye adsorption study of manganese and samarium doped and co-doped zinc sulfide phosphors

      2020, Optical Materials
      Citation Excerpt :

      To date, many synthesis methods have been reported for preparing ZnS nanocrystals. For examples, (1) chemical precipitation for synthesizing pure ZnS and Ni2+ doped ZnS [20], (2) solvothermal method for Au and Ag-doped ZnS [3], (3) hydrothermal method for ZnS [21] and Mn-doped ZnS [22], (4) sol-gel method for Mn-doped ZnS [23], (5) mechanochemical method for pure ZnS [24], (6) reverse micelle method for Mn-doped ZnS [25], and (7) microwave-assisted method for Zr, Rh and Pd doped ZnS [26]. Among all synthetic routes, the chemical precipitation is a promising method with advantages over others.

    • Structural, morphological and optical properties of Cr doped ZnS nanoparticles prepared without any capping agent

      2020, Optik
      Citation Excerpt :

      The band gap and band structure convert because increases in band gap and decreases in practical size with the edges of the band split into discrete energy levels [1,2]. One of the successful processes employed to improve the optical properties of semiconductors is doping [15–18]. Impurity states that may take place due to the doping may change the optical properties of semiconductor nanoparticles.

    • Fabrication of Schiff base coordinated ZnS nanoparticles for enhanced photocatalytic degradation of chlorpyrifos pesticide and detection of heavy metal ions

      2019, Journal of Materiomics
      Citation Excerpt :

      In recent years, the development of novel fluorescent sensors has attracted significant interest for selective and sensitive detection of metal ions in environmental and biological samples [29]. Therefore, previously reported the ZnS NPs is an important luminescence material with a wide band gap, widely used in fluorescence sensing applications and in particularly it suitable for the detection of heavy metal ions [30]. From the background literature, it has been found that several studies are available on the degradation of toxic pollutants as well as detection of metal ions using semiconductor nanostructures with various supporters or capping agents but very few studies are reported on Schiff base capped semiconductor nanostructures.

    View all citing articles on Scopus
    View full text