Fe doped ZnO nanostructures prepared by co-precipitation method

Journal Pre-proof Structural, magnetic and photoluminescence behavior of Ni/Fe doped ZnO nanostructures prepared by co-precipitation method C. Prabakar, S. Muthukumaran, V. Raja

PII:

S0030-4026(19)31612-2

DOI:

https://doi.org/10.1016/j.ijleo.2019.163714

Reference:

IJLEO 163714

To appear in:

Optik

Received Date:

4 August 2019

Revised Date:

24 October 2019

Accepted Date:

5 November 2019

Please cite this article as: Prabakar C, Muthukumaran S, Raja V, Structural, magnetic and photoluminescence behavior of Ni/Fe doped ZnO nanostructures prepared by co-precipitation method, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.163714

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Structural, magnetic and photoluminescence behavior of Ni/Fe doped ZnO nanostructures prepared by co-precipitation method C. Prabakar, S. Muthukumaran*, V. Raja PG & Research Department of Physics, Government Arts College, Melur -625 016, Madurai, Tamilnadu, India

*

Corresponding author. Tel.: +91 +91 0452 2415467; fax: +91 0452 2415467.

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E-mail address: [email protected] (S. Muthukumaran)

Abstract

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Un-doped and Ni/Fe-doped ZnO nanostructures were synthesized by co-precipitation route. The variation in crystallite size and lattice parameters by Ni/Fe doping is discussed by the

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dissimilarity in their ionic radius and the generation of defect states. The higher energy gap in

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Fe-doped Zn0.97Ni0.03O is described by the generation of oxygen related defects. The shifting of IR frequency by Ni/Fe-doping confirmed the Ni/Fe ions are replaced at tetrahedral sites

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instead of octahedral co-ordination. The high intensity green emission at  524 nm from PL study confirmed the increased oxygen vacancies related defects in Ni, Fe dual doped ZnO.

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Though the entire samples exhibited room temperature ferromagnetism (RTFM), Ni, Fe dual doped ZnO showed the strong ferromagnetism due to the existence of the oxygen vacancy

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mediated bound magnetic polarons (BMP). Keywords: Dual doped ZnO; Tuning of energy gap; Photoluminescence; Room temperature ferromagnetism

______________________ 1. Introduction

Metal oxide (MO) like zinc oxide (ZnO) possesses unique characteristics like low resistivity, high energy band gap [1], and high chemical stability [2] which promotes them to potential technological applications [3-5]. The magnitude of room temperature saturation 1

magnetization in undoped ZnO is small which restricted them to the practical applications [6]. The addition of transition metal (TM) into ZnO is an effective technique to adjust the physical properties of ZnO. The characteristics like optical and magnetic nature can be adjusted using the addition of TMs like Fe [7], Co [8], Mn [9], Ni [10] and Cu [11]. The TM ions like Co, Mn and Ni added ZnO nanoparticles found some applications in spintronic materials [12]. The surface modification by TMs like Al, Mn, Co, Cr, Ni, Fe, and Cu [13, 14] has revealed a enormous impact on optical, magnetic and sensing applications [15, 16].

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Among the different TM ions, Ni2+ exhibits higher chemical stability during the occupation of Zn2+ place and improves the electrical nature [17]. Cong et al. [18] detailed the

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ferromagnetic nature of Ni added ZnO. The substitution of Zn2+ through Ni2 gives up high

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donor defects and improves the transport nature [19]. The doping of Ni not only stimulates a change in magnetic properties [20], but also makes red shift in the energy gap [21]. The

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collective effects of optical and magnetic properties, makes it a key source for the optical

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integrated circuit applications [22]. Therefore, in the present work, Ni is selected as first doping element in order to enhance the optical and structural characters of ZnO. To avoid the

to 3%.

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secondary phases and also to maintain the solubility limit of Ni in ZnO [23], doping is limited

The simultaneous substitution of two TM ions in ZnO is a significant technique to

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achieve the better optical and structural properties [24]. For that reason, the scientists take immense efforts in the dual doping of TM ions in ZnO [25]. Among the different TM elements, Fe is selected as the second doping element into ZnO because of the following reasons: (i) the ionic radius of both Fe2+ (0.76 Å) and Fe3+ (0.64 Å) are analogous to Zn2+ (0.74 Å) which is used to reduce the lattice distortion [26] and (ii) the substitution of Fe induce additional impurity levels in the host lattice which improve the energy level structure. Xu et al. [27] noticed that the small amount of Fe (1%) substitution enhanced the crystal 2

nature and ultraviolet emission in ZnO. Chen et al. [28] described that Fe doping could significantly influence the physical nature of ZnO because of the adjustment of Fe valence state from Fe3+ to Fe2+. Beltrán et al. [29] inspected the magnetic properties of single Fe / Co doped ZnO and Fe, Co dual doped ZnO. Singh et al. [30] reported the enhancement in optical band gap in Fe, Co dual doped ZnO than undoped ZnO. Recently, Fe/Co dual doped ZnO has been studied to analyze the magnetic properties of the system [29]. In recent days, Fe, Ni-doped ZnO/

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material for waste water treatment and anti-microbial agent [31].

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polyaniline composite has been studied and it has been observed that it acts as effective

Even though, the detailed optical and structural studies have been reported on single

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Ni/Fe doped ZnO [17-28], the detailed study about optical, structural, magnetic and

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photocatalytic studies on Ni, Fe dual doped ZnO nanostructure is nearly scantly. Therefore, Ni-doped and Ni/Fe dual doped ZnO nanostructure have been successfully prepared by

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chemical co-precipitation method. The role of Ni/Fe on the structural, optical, magnetic and photocatalytic behavior in ZnO were investigated systematically.

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2. Materials and experimental procedure

2.1. Synthesize of ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanostructures

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For the preparation of Zn0.95Ni0.03Fe0.02O nanostructures zinc acetate dihydrate

[Zn(CH3CO2)2.2H2O], nickel nitrate (Ni(No3).6H2O) and ferric chloride dihydrate (FeCl2.2H2O) are usedas metal precursors and sodium hydroxide (NaOH) is used to control the pH value. The prepared NaOH solution was added drop wise to the initial solution to increase the pH to 8.5. The preparative technique is reported in the literature [32]. Final powders were annealed at 500˚C in air atmosphere for 2 h followed by furnace cooling. 2.2. Characterization technique 3

XRD patterns were recorded by RigaKu C/max-2500 diffractometer from 2θ = 30˚ to 70˚. The topological features and composition were determined by energy dispersive X-ray (EDX) spectrometer. The surface morphology was studied using a scanning electron microscope (SEM, JEOLJSM 6390). The optical absorption and transmittance were determined using UV–Visible spectrometer (Model: lambda 35, Make: Perkin Elmer) from 300 nm to 700 nm. The chemical bonding was studied by Fourier transform infra red (FTIR) spectrometer (Model: Perkin Elmer, Make: Spectrum RX I) from 400 to 4000 cm-1. The

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photoluminescence (PL) spectra have been carried out between the wavelength ranging from

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350 to 600 nm using a fluorescence spectrophotometer (F-2500, Hitachi). The magnetization (M) and magnetic hysteresis (M-H) loops were measured at room temperature using vibrating

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sample magnetometer (VSM, Make: Lake shore, Model: 7404). 3. Results and discussion

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3.1. XRD - Structural studies

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The modulated XRD pattern by the influence of Ni/Fe in ZnO is revealed in Fig. 1a. The crystallization of the synthesized samples with hexagonal structure is confirmed by unique and high intensity XRD peaks. All the samples possess wurtzite structure of ZnO [33].

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Moreover, no peaks matching to Ni/Fe or its oxides like NiO/Fe2O3. The noted high peak intensity and narrow peak widths expressed that all the synthesized samples possess nano-

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sized crystalline nature [34]. The slight enhancement in XRD peak intensity along (101) plane (higher along the entire samples) of Ni-doped ZnO than pure ZnO is due to the substitution of comparably smaller Ni2+ ion at Zn2+ sites. The modulation in XRD intensity is clearly exposed by Fig. 1b for different peak position between 35.2° and 37.2°. Fig. 1c shows the graphical representation of the alteration in peak intensity and crystallite size of different synthesized samples. The changes in XRD derived parameters such as peak position and intensity, full width at half maximum (FWHM) along (101) plane, crystallite size and micro4

strain of different synthesized samples is displayed in Table 1. During the doping of Ni into ZnO (Zn0.97Ni0.03O), it is observed that both the peak position shifted towards 2 side and the peak intensity slightly increased to higher value as illustrated in Fig. 1b. In general, the increase of peak intensity indicates the increase of crystallite size. But in this case, size gets decreased by Ni-doping than pure ZnO which is mainly due to the enhancing full width at half maximum (FWHM) value and micro-strain. The average crystallite size is derived from Scherrer’s formula D = 0.9/cos and

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the micro-strain (ε) is obtained by[32]  = cos/4. The inclusion of Fe into Zn0.97Ni0.03O

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diminishes the intensity of all the peaks and shift the peak position which may be due to the disorder or defects generated by the addition of Fe2+ ions in Zn-Ni-O sites. The similar

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decrease of peak intensity is reported by Kayani et al. [36]. It is well-known that the radius of Fe2+ ions is larger than that of ionic radius of Zn2+ and Fe3+ ions has smaller ionic radius than

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Zn2+ [37]. It is noted from Table 1 that the enhanced size and diminishing FWHM and micro-

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strain values by simultaneous doping of Fe into Zn-Ni-O are due to the replacement of Fe2+ instead of Zn2+.

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The modulation in d-value, cell parameters ‘a’ and ‘c’, c/a ratio, and volume of ZnO, Zn0.97Ni0.03O, and Zn0.95Ni0.03Fe0.02O nanoparticles is expressed in Table 2. The inter-planar

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distance 'd' is obtained from the diffraction theory, 2d sin  =, and the lattice parameters like 'a' and 'c' are derived from the relation [38] 1/d2 = 4/3 ([h2+hk+k2]/a2) +l2/c2. The unit cell volume (V) can be obtained from the relation [39], V = 0.866 x a2 x c. The small re-allocation in the positions of the XRD peaks lead the increase of lattice parameters which indicate the successful inclusion of Ni2+ into Zn-O site [17]. The lattice parameters, 'd' value and volume are further enhanced by Fe-doping in Zn-Ni-O lattice. When Fe is introduced into Zn-Ni-O sites, the generation of the interstitial atoms as well as the variation in radius of Zn and Fe 5

ions led to lattice distortion which might enhance the lattice parameters. C. Han et al. [26] reported that Fe2+ exists at lower Fe concentration and Fe3+ presents at higher Fe concentrations of Fe-doped ZnO. The noticed increase of lattice constant in the present system confirm the substitution of Fe2+ with larger ionic radius in the position of Zn2+ [28]. As noticed from Table 2 the overall c/a ratio is nearly constant and approximately no variation is noted within the entire samples which recommends that Ni2+ / Fe2+ ions are properly included into Zn-O sites, without changing its crystal structure [40].

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3.2. Microstructure and Compositional analysis

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The surface morphology of pure ZnO, Ni-doped ZnO, and Ni, Fe dual doped ZnO nanostructure was made by SEM, and SEM images are shown in Fig. 2a-c. Fig. 2a show the

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surface morphology of pure ZnO which exhibit an agglomerated more or less spherical like structure with un-even size around 20 nm. When Ni is included into ZnO, the grain size

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reduced to  10-15 nm with more agglomeration as shown in Fig. 2b. The lattice distortion

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and the defect induced by Ni2+ in Zn-O site is accountable for the diminution of size. Fig. 2c illustrates the SEM image of Zn0.95Ni0.03Fe0.02O sample. Dual doping of Ni and Fe into ZnO

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slightly enhances the size as shown in Fig. 6c with more agglomeration. The EDX spectra and its elemental analysis of pure ZnO, Zn0.097Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles are illustrated in Fig. 2 d-f. It is explored from Fig. 2 d-f that

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no signal of the unwanted additional elements except Zn, O, Ni and Fe was observed. The atomic % of the elements, (inset of Fig. 2d) Zn and O are nearly equal for pure ZnO and the percentage of Zn gradually decreased by single (inset of Fig. 2e, Ni-doping) and double (inset of Fig. 4c, Ni and Fe simultaneous doping) element doping into ZnO. The atomic % of Ni/(Zn+Ni) and Fe/(Zn+Ni+Fe) ratio confirms the well-incorporation of Ni/Fe into ZnO. 3.3. UV-Visible spectroscopy - Optical properties

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The room temperature absorption spectra of un-doped and Ni/Fe doped ZnO as carried out from 300 nm to 700 nm and displayed as shown in Fig. 3a. The absorption edge of the whole range of the samples found below 340 nm even though the band gap pure ZnO ≈ 3.3 eV (matching wavelength at 370 nm) [41]. The obtained lower absorption edges in this work than the bulk ZnO confirms the existence of nano-dimension in the synthesized samples. The absorption intensity of pure ZnO enhanced by Ni-doping (single doping) and further elevated by Ni, Fe double doping. The higher intensity at single/double doping is due

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to the replacement of Zn2+ instead of Ni2+ / Fe2+ in ZnO lattice [42]. The similar increase of

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absorption intensity is noticed in Ni-doped ZnO [42] and Ni, Mn doped ZnO [6]. The existing broad absorption band centered at 488 nm is because of the d-d transition in Ni/Fe-

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doped ZnO [43] which indicates the substitution of Ni2+/Fe2+ in the tetrahedral of ZnO [44]. Room temperature transmittance spectra of un-doped and Ni/Fe doped ZnO from 300

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nm to 700 nm are presented in Fig. 3b. All the three samples exhibit lower transmittance at

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lower wavelength and superior transmittance at higher wavelength particularly after 488 nm. The continuous decrease of transmittance by doping Ni alone and Ni, Fe dual doping into ZnO is due to the generation of defect states by dopant. The optical band gap of the

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synthesizes samples was obtained by using the Tauc relation [45] hυ = A(hυ - Eg)n. The optical energy gap is obtained from a graph between (αhυ)2 and hυ as shown in

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Fig. 4a. Optical energy gap exhibits clear blue shift i.e., continuous increase from 3.97 eV (un-doped ZnO) to 4.05 eV for Zn0.97Ni0.03O and 4.09 eV for Zn0.95Ni0.03Fe0.02O nanostructures. The same type of increase in energy gap by Ni doping at lower concentration was reported by Jeyachitra et al. [46]. The enhanced energy gap is ascribed to the BursteinMoss band filling effect [47-49] that is obviously observed in n-type ZnO. During the doping of Fe in addition to Ni, the Fermi level moves towards the direction of conduction band because of the sp-d exchange relations among the band electrons and localized spin of Fe2+ 7

ions [50]. The exchange interaction generates the excess carriers which engage the states close to the Fermi level in the conduction band and hence energy gap further shift to higher level [51] as shown in Fig. 4a. Both Kumar et al. [52] and Liu et al. [53] reported the same blue shift of energy gap in Fe doped ZnO. Fig. 4b illustrates the change in crystallite size and energy gap of un-doped and Ni/Fe doped ZnO. When Ni is introduced into ZnO (Zn0.97Ni0.03O) energy gap enhanced to higher value at the same time size of the nanoparticles diminished to lower value i.e., it obey the size

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effect [54]. During Ni and Fe dual doping, both size and energy gap enhanced to higher

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value. Since, the size of nanoparticles are much higher than the excitonic Bohr radius of the host material, size has negligible role in the modification of energy gap. Further, it is

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concluded that the incorporation of simultaneous Ni and Fe into ZnO change the structure of the system and generate the oxygen related defects [55].

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3.4. Fourier transform infrared spectroscopy (FTIR) analysis - Chemical bonding

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Fig. 5 expresses the FTIR spectra of ZnO and Ni/Fe-doped ZnO within 400-4000 cm-1. Throughout the samples, the presence of H-O-H from moisture and the atmospheric CO2 is not avoided. The noticed wide and high intensity bands between 3000-3700 cm-1 are

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due to polymeric O-H stretching vibration of H2O in Ni/Fe-Zn-O lattice [56]. The band in the region of 2330 cm-1 is corresponding to M-CO stretching mode [57, 58], here M represents

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the transition metal element. The sharp bands around 1569 cm-1 are payable to the bending vibration of O-H [59]. The peaks in the region of 1338 cm−1 are owing to the vibration of C=O group [60]. The observed feeble bands around 700-1000 cm-1 are payable to the vibrations corresponding to defect states and local bonds induced by Ni/Fe in Zn-O lattice [61-63]. The absorption band lower than 700 cm−1 are usually originated from the bond between inorganic elements i.e. metal-oxide (M-O) bonding. It is well-known that the peaks 8

around 600-650 cm−1 and 400-460 cm−1 are due to the stretching vibration mode of Zn-O in tetrahedral and octahedral co-ordinates [64, 65] respectively. The characteristic peak around 470 cm−1 found in ZnO represents the stretching vibration of Zn-O in octahedral coordination. When Ni is introduced into ZnO, the characteristic peak shifted to 520 cm−1 and further shifted to 560 cm−1 for Fe/Ni-doping. The shifting of frequency towards higher wave number by Ni/Fe-doping confirmed that the Ni/Fe ions are replaced simply at tetrahedral arrangement instead of octahedral co-ordination in ZnO. In addition, the shift may be due to

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the dissimilarity in bond lengths by Zn2+ ions replaced by Ni2+/Fe2+ with different ionic

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radius [66]. 3.5. Photoluminescence spectroscopy

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The PL spectra of un-doped ZnO, Ni/Fe doped ZnO between 350 nm and 600 nm at room temperature is presented in Fig. 6a. Here, ZnO consists of four emission bands namely,

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two UV emissions centered at 359 nm and 383 nm, blue emission at 478 nm and green

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emission at 524 nm. The noticed high energy UV bands are originates from the radiative recombination of free excitons from localized level near the condition band to the valence band corresponding to NBE emission [67-69]. The visible PL emissions like violet, blue and

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green are deep-level emissions induced by different defect states such as oxygen vacancies (VO), zinc vacancies (VZn), zinc interstitials (Zni), etc. [70]. The origin of feeble blue band

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emission at 478 nm ( 2.60 eV) in ZnO is due to the transition from one intrinsic defect state to another state, particularly interstitial zinc (Zni) to acceptor level of neutral VZn near valence band [71, 72]. The observed green band at 524 (~ 2.37 eV) is induced from the recombination of electron with h+ (holes) trapped in singly ionized VO [73-75]. Vanheusden et al. [76] reported that the green band in ZnO is originated from the recombination of h+ and the electron of a singly ionized VO. The energy level diagram to describe the emissions of UV, violet, blue and green colours in Zn0.95Ni0.03Fe0.02O sample is displayed in Fig. 6b. 9

The luminescence intensity increases and also UV band shifted to higher wavelength side when Ni/Fe is introduced into ZnO than un-doped ZnO which is mainly due to the increasing number of distortion centers produced in Zn-O lattice [55, 77]. Moreover, the UV shoulder bands are found around 415-421 nm in Ni/Fe-doped ZnO which are missed at undoped ZnO. The violet band is corresponds to zinc vacancies. The position of Zni is just below the conduction band and the gap difference between Zni and valence band is 3.0 eV [75]. Hence, the violet emission is originated from the transition between Zni and the top level

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of valence band. Shi et al. [78] and Kumar et al. [79] reported the similar violet band which is

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related to trapping states in grain boundaries. The intensity of visible emissions like blue and green is increased by Ni/Fe doping in ZnO which confirmed the increased oxygen vacancies

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related defects in the prepared samples. 3.6. Magnetic properties

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Fig. 7a reveals the graph between magnetization and magnetic field (M-H) of un-

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doped ZnO, Ni/Fe doped ZnO at room temperature from H = -3000 to 300 Oe. Room temperature ferromagnetic (FTFM) behavior is noticed in the entire samples where the magnitude of magnetization is minimum for un-doped ZnO which is enhanced by Ni-doping

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and also by Ni, Fe dual doping. The exchange interface among the spin-polarized electrons and conductive electrons [80] and bound magnetic polarons (BMP) produced from point

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defects like interstitials, oxygen vacancies [81] are the potential reasons of current RTFM. The increasing saturation magnetization by Ni-doping and Ni, Fe-dual doping signifying that the substitution of TM ions enhance the RTFM. The presence of secondary phases like NiO / Fe2O3 or other metallic oxide phases may

responsible for the RTFM. But, the existence of MO phases is ruled out from XRD measurements where no extra peaks detected. As a result, the FM character noticed in the current samples is only due to the intrinsic nature. Fig. 7b illustrates the variation in retentivity 10

and coercivity of un-doped ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanostructures. The gradual decrease of coercivity and the steady increase of retentivity are noticed with Ni/Fedoping. It is well known from Fig. 7b that Zn0.95Ni0.03Fe0.02O sample exhibits maximum retentivity and low coercivity values which confirms the occurrence of higher defect states. The previous studies recommend that the oxygen vacancies play a significant role in mediating the long - range magnetic exchange coupling in DMSs [82]. The oxygen vacancies are intrinsically present in Ni/Fe doped ZnO without any structural volatility. Therefore, the

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oxygen vacancy mediated BMP [83] acting a main role in the origin of RFTM in the Ni/Fe

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doped ZnO. During Fe-doping in Zn0.97Ni0.03O lattice, the FM interaction among the Fe ions becomes stronger due to the reduced lattice distance between Fe-Fe ions [84]; the present

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stronger interaction enhanced the saturation magnetization. Further, the exchange interaction between conductive electrons with local spin polarized electrons on Ni2+/Fe2+ ions from RKKY

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theory (RKKY stands for Ruderman-Kittel-Kasuya-Yosida) is also accountable for RTFM.

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4. Conclusions

Un-doped ZnO and Ni/Fe-doped ZnO nanostructures have been synthesized by coprecipitation route. The variation in crystallite size and lattice parameters by Ni/Fe doping is

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discussed by the dissimilarity in their ionic radius and the generation of defect states. The constant c/a ratio within the entire samples recommended that Ni2+ / Fe2+ ions are properly

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included into Zn-O sites. The noted higher energy gap with absorption intensity in Fe-doped Zn0.97Ni0.03O system is due to the generation of oxygen related defects. The shifting of frequency towards higher wave number side by Ni/Fe-doping in FTIR spectra confirmed that the Ni/Fe ions are replaced simply at tetrahedral arrangement instead of octahedral coordination in ZnO. The high intensity green emission at  524 nm from photoluminescence (PL) study confirmed the increased oxygen vacancies related defects in Ni, Fe dual doped ZnO samples. Though the entire samples exhibited room temperature ferromagnetism (RTFM), Ni, 11

Fe dual doped ZnO showed the strong ferromagnetism which is induced from the existence of the oxygen vacancy mediated bound magnetic polarons (BMP).

Declaration of interest Please find enclosed one of my research papers for the publication in your journal. The work

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described is original and has not been published previously in any language, either partially

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or wholly. Submission also implies that the work is not under consideration for publication elsewhere, that its publication is approved by all authors and that, if accepted, it will not be

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published elsewhere, in English or in any other language, without the written consent of the

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Publisher. It also implies that all authors had full access to all of the data in the study and take complete responsibility for the integrity of the data and the accuracy of the data

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Dr. S. Muthukumaran

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analysis.

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.

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Figure captions Figure 1. (a) XRD pattern of between 30° and 70°, (b) Enlarged view of XRD pattern from 35.2° to 37.2°, (c) the variation of XRD peak intensity and average crystallite size of pure ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles. Figure 2. SEM images of (a) pure ZnO, (b) Zn0.97Ni0.03O and (c) Zn0.95Ni0.03Fe0.02O nanoparticles. EDX spectra of (d) pure ZnO, (e) Zn0.97Ni0.03O and (f) Zn0.95Ni0.03Fe0.02O nanoparticles. The inset shows the atomic percentage of the constituent elements.

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Figure 3. UV-Visible (a) absorption spectra and (b) transmittance spectra of pure ZnO,

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Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles from 300 nm to 700 nm.

Figure 4. (a) The (αh)2 versus h curves of pure ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O

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nanoparticles for the optical energy gap calculation, (b) the variation of average crystallite size and energy gap of pure ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles.

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Figure 5. FTIR spectra of pure ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles at

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room temperature from 400 cm-1 to 4000 cm-1.

Figure 6. (a) The room temperature PL spectra of pure ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles as a function of wavelength between 350 nm and 600 nm,

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(b) the energy level diagram to describe the UV, violet, blue and green light emissions in Zn0.95Ni0.03Fe0.02O sample.

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Figure 7. (a) Magnetization versus magnetic field (M-H) curves of pure ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles at room temperature, (b) variation in coercivity and retentivity of pure ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O.

21

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Table 1 The variation in XRD peak position, peak intensity, FWHM along (101) plane, average

Peak

Micro-

position,

intensity

crystallite size, D

strain, ε

2θ (˚)

(counts)

(nm)

(10-3)

ZnO

36.35

6448

0.62

15

2.363

Zn0.97Ni0.03O

36.26

6628

0.68

12

Zn0.95Ni0.03Fe0.02O 36.04

5547

0.60

14

FWHM, β

2.944 2.490

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(degrees)

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Peak Samples

Average

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crystallite size and micro-strain of ZnO, Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles

Table 2

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The variation in d-value, cell parameters ‘a’ and ‘c’, c/a ratio, and volume of ZnO,

Samples

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Zn0.97Ni0.03O and Zn0.95Ni0.03Fe0.02O nanoparticles

d-value

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(Ǻ)

Cell parameters (Ǻ)

c/a ratio

Volume, V (Ǻ)3

a=b

c

ZnO

2.4695

3.2636

5.2228

1.600

48.1743

Zn0.97Ni0.03O

2.4755

3.2664

5.2278

1.600

48.3032

Zn0.95Ni0.03Fe0.02O

2.4901

3.2687

5.2350

1.602

48.4378

29