Impact Of Doping Transition Metal In Optically Sensitive CuS with As Prepared CuS

T.V. Banumathi 1,a) and J. Sree Sudha1, b)

1Department of Physics, Sri G.V.G Visalakshi College for Women, Autonomous, Udumalpet, Tamilnadu, India a) tvba64@gmail.com

b) jsreesudha2012@gmail.com a)Corresponding author: tvba64@gmail.com

b)jsreesudha2012@gmail.com

Abstract. The CuS and the transition metal Mn doped CuS were synthesized by co-precipitation method using Cupric Chloride Hydrate, Triethanolamine, Thiourea and Manganese (II) Chloride tetrahydrate. The prepared samples of Mn-CuS were calcinated at 150 0C and 300 0C. The structural and optical properties of CuS and Mn-CuS were investigated through XRD, FTIR, SEM with EDAX, UV absorption and PL. The XRD studies revealed the crystalline nature of CuS and Mn-CuS and the lattice parameters were also calculated. The FTIR spectra show the presence of Mn in Mn-CuS. The band gap energies of the samples were calculated using Tauc plot of UV absorption results and the Photoluminescence study showed the emission wavelength peaks of the samples. Keywords: Transition metal, optical properties, band gap, Tauc plot, Photoluminescence, emission wavelength.

1.INTRODUCTION

Nano materials unveil number of optical, electrical, magnetic and chemical properties which greatly differs from bulk materials because of their unique size which leads to the applications in the technological fields [1-3]. Research has been going on for several decades and also has successfully emerged in industrial applications. Copper Sulfide is also one of the prominent nano material which exhibits excellent optical, surface and structural properties [4]. Copper sulphide is an inorganic compound of general formula CuxSy. It can be classified as Copper monosulfide, disulfide and mixed monosulfide. It crystallizes in hexagonal structure and in the form of covellite which is a natural one. CuS is widely used for the applications in Solar cells, gas sensors, photoconductors, photocatalysts and lithium – ion batteries and also as electrodes [5-10]. The controlled synthesis by various methods [11–18] and with different CuS compounds the attracted potential applications has come into existence. The properties and the characterization of any nano material enhance or change by doping or forming composites with other compounds or elements [19]. Likewise the properties and characteristics of CuS can be improved by doping with other elements (transition elements) like Zn, Mn, Ti, Co, Ca, and Ni. Here, Mn is used for doping CuS, which increases the size of the surface area and reduces the particle size and also boosts the photolytic properties [20].

In the present work, the synthesis of CuS and Mn doped CuS nano particles using the precursors CuCl 2.2H2O, NH2CSNH2, MnCl2 4H2O and C6H15NO3 has been carried out by co-precipitation method to understand the impact of the transition element over the as-prepared CuS. Here Cupric Chloride Hydrate, Thiourea and Manganese (II) Chloride tetrahydrate act as sources of Cu, S and Mn. The obtained nano particles have been characterized using XRD, FTIR, SEM with EDAX, UV and PL.

2. Experimental Details

2.1 Synthesis of CuS Nanoparticles

CuS nanoparticle is prepared by precipitation method. 5 mlof CuCl 2.2H2O mixed with 8 ml of C6H15NO3 is stirred continuously. 10 ml of ammonia solution is added while stirring and continued for 10 minutes. Later under the stirring process, 10 ml of NaOH is added followed by 6 ml of NH 2CSNH2 and left for 10 minutes. Double distilled water is added to make the final solution 100 ml and stirred continuously at room temperature for 3 hrs. The precipitate thus formed is filtered and washed with distilled water several times. It is dried at 90 0C for 24 hrs and grounded well using pestle-mortar to obtain the final form of CuS nanoparticles.

2.2 Synthesis of Mn Doped CuS Nanoparticles

Mn doped CuS nanoparticle is synthesized by precipitation method. 5 ml of CuCl2.2H2O mixed with 5 ml of MnCl2 4H2O is allowed to stir at room temperature. 8 ml of C 6H15NO3 is added in the above solution while stirring. 10 ml of ammonia solution is added drop-wise followed by 10 ml of NaOH. Further 6 ml of NH 2CSNH2 is added and left to stir for another 10 minutes. Double distilled water is added to make the final solution 100 ml and stirred continuously at room temperature for 3 hrs. The thus formed precipitate is filtered and washed with distilled water several times. It is dried at 90 0C for 24 hrs to obtain the final product of Mn doped CuS nanoparticles. The Mn-CuS is calcinated at 150 0C and 300 0C separately. The structural and optical studies have been carried out for the samples.

3. Results and Discussions

3.1 Structural Analysis

The XRD spectrometer is used in the recording of the diffracted pattern of the samples using CuKα radiation operated between 3deg. and 95deg. The structural analysis is carried out using the Debye-Scherrer formula of FWHM. Figure 1 represents the XRD pattern for the samples of CuS and Mn doped CuS (150 0C and 3000C). The observed XRD parameters in the present work are well matched with JCPDS card number: 04-0464 which reveals the crystalline nature and also possess the Hexagonal structure [4]. The average crystalline size is found to be 29.46 nm for pure CuS and 27.93 nm, 24.94 nm for Mn doped CuS at 150 0C, 300 0C respectively. The crystallite sizes is found to decrease for the Mn doped CuS. Also the process of calcination seems to reduce the crystallite size. The plane (1 0 8) is confirmed for undoped CuS and the plane (2 0 3) is confirmed for Mn doped CuS nanoparticles. The lattice parameter a = b = 3.22 A0 and c = 2.6 A0 is calculated. The 150 0C of Mn-CuS nanoparticles have sharp peaks compared to 300 0C of Mn-CuS nanoparticles [19-20].

FIGURE 1 : XRD spectrum for undoped and Mn doped CuS (1500C & 3000C)

3.2 Fourier Transform Infrared spectroscopy (FT-IR):

The FTIR analysis is carried out using JASCO FTIR Spectrometer.The peak observed at 1211 cm -1and 1197 cm-1

of Mn-CuS calcinated at 150 0C and 3000C respectively denote Mn=N stretching due to the presence of Manganese Chloride. The peak at 1370 cm-1 (a) and 1365 cm-1 (c) corresponds to the NO2 nitro groups.

FIGURE 2: FTIR spectrum of (2a) as-prepared CuS, 2b) Mn doped CuS at 150 0C 2c) Mn doped CuS at 300 0C

3.3 Surface Analysis: Scanning Electron Microscope (SEM)

The SEM micrograph of as-prepared CuS and Mn-CuS (150 0C) are shown in the figures below

FIGURE 3.a) SEM images of as-prepared CuS nanoparticles

Fig. 3.b): SEM images of Mn-CuS (150 0C) nanoparticles

The as-prepared CuS nanoparticles are agglomerated while that of Mn doped CuS nanoparticles have spherical morphologies. The change in the morphology is due to Mn ions replacing Cu ions in CuS lattice sites. This confirms the doping of Mn ions in CuS nanoparticles matrix. The variation in the copper content leads to change in the morphology of the nanoparticles, which is proved here by the Mn being doped in CuS crystal structure [4–7].

3.4 Energy Dispersive Analysis of X-rays (EDAX)

Fig 4: EDAX spectrum for (4a) As-prepared CuS and (4b) Mn- CuS (150 0C) nanoparticles

The chemical compositions of the as-prepared CuS and Mn doped CuS nanoparticles are studied with the help of EDAX. Only Copper and Sulphur peaks are observed in the CuS spectrum. In the Mn doped CuS nanoparticles of figure 4(b), Manganese and Oxide peaks are observed. The observed weight percentage values are nearer to the standard theoretical weight percentage values. The weight percentage values are shown in the Table below.

Sample Element Weight % Atomic %

CuS Cu 63.03 47.06

S 30.97 52.94

Mn-CuS O

S

Mn

Cu

21.37

20.91

3.60

54.12

45.98

22.45

2.25

29.32

TABLE:1 Elemental composition for As-prepared CuS and Mn doped CuS

3.5 Optical studies

3.5.1 Ultraviolet–Visible Spectroscopy

The Tauc plot of (αhν)2 versus (hν) for as-prepared CuS and Manganese doped CuS nanoparticles are shown in figure 5. The optical band gap values of 4.1 eV for as-prepared CuS and 3.6 eV for Mn-CuS nanoparticles at (150 0C), and 3.3 eV for (300 0C) is calculated. The optical band gap value of the as-prepared CuS nanoparticles is higher compared to the Mn doped CuS at nanoparticles at 150 0C and 300 0C. And also on increasing calcination temperature the band gap energy of the Mn doped CuS is found to decrease. This reveals the impact of temperature and the dopant on the Mn doped specimen of CuS [19, 21].

FIGURE 5 : Tauc plot of 5a) as-prepared CuS 5b) Mn doped CuS(1500C) 5c) Mn doped CuS(3000C)

3.5.2 Photoluminescence (PL) spectroscopy

Figure 6 shows the photoluminescence (PL) spectra of nanoparticles of as-prepared CuS and Mn doped CuS recorded in the wavelength range 350 -500nm.

FIGURE 6: The Photoluminescence spectra of as-prepared CuS and Mn-CuS Nano particles.

The PL spectrum shows the emission of blue light which is observed at the peak 387 nm and 419 nm and also Mn doped CuS nanoparticles have two emission peaks at 410 nm and 435 nm [1,2,4]. Comparing PL spectrum for as-prepared CuS and Mn doped CuS nanoparticles, as-prepared CuS nanoparticles shift towards the shorter wavelength.[25]

4. Conclusion

The as-prepared CuS and Mn doped CuS nanoparticles are synthesized using co-precipitation method. The XRD analysis of as-prepared and Mn doped CuS nanoparticles confirms the crystalline nature and hexagonal structure. The average particle size is determined as 29.46 nm for as-prepared CuS and 27.93 nm, 24.94 nm for Mn-CuS at 150 0C, 300 0C respectively. Also the lattice parameters are calculated as a = b = 3.22 A 0 and c =2.6 A0. The FT-IR spectrum confirms the presence of Mn=N stretching in CuS and Mn-CuS nanoparticles. From UV-Vis, both the undoped (as-prepared) and Mn doped CuS nanoparticles possesses direct optical band gap energy of 4.1eV for CuS and 3.6 eV and 3.3 eV at 150 0C , 300 0C of Mn doped CuS respectively. The SEM images clearly showed that the CuS nanoparticles are agglomerated in shape whereas Mn doped CuS have spherical like morphologies. The undoped (as-prepared) and Mn doped CuS nanoparticles is confirmed by EDAX analysis which confirms the presence of Cu, Mn, S and O contents. The band gap value of CuS nanoparticles (4.1 eV) is more than the doped CuS nanoparticles with 3.6 eV and 3.3 eV for 150 0C and 300 0C calcinations which could be desirable aspect for photocatalytic actions. The PL spectra reveals the emission of blue wavelength and showed two emission peaks at 387nm and 417 nm for undoped (as-prepared) and at 410nm and 435 nm for Mn-CuS nanoparticles.

ACKNOWLEDGMENTS

The authors sincerely acknowledge the Management, the Principal and the Head of the Department of Physics of Sri GVG Visalakshi college for women, Udumalpet, TN,India for providing encouragement and facilities to carry out the research effectively. The authors thankfully acknowledge the DST for providing funding under DST-FIST (Level 0) scheme to the institution for procuring JASCO-FTIR Spectrometer. The authors also acknowledge the services of the Instrumentation centres of the universities CUSAT, BU for providing the results at the earliest.

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