Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite

Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite

Journal Pre-proof Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite Mohamed Bakr Mohamed, M...

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Journal Pre-proof Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite

Mohamed Bakr Mohamed, M.H. Abdel-Kader PII:

S0254-0584(19)31100-9

DOI:

https://doi.org/10.1016/j.matchemphys.2019.122285

Reference:

MAC 122285

To appear in:

Materials Chemistry and Physics

Received Date:

04 March 2019

Accepted Date:

07 October 2019

Please cite this article as: Mohamed Bakr Mohamed, M.H. Abdel-Kader, Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite, Materials Chemistry and Physics (2019), https://doi.org/10.1016/j.matchemphys.2019.122285

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Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite Mohamed Bakr Mohameda,b, M.H. Abdel-Kadera,b,* a

Physics Department, Faculty of Science, Taibah University, Al-Madina al Munawarah, Saudi Arabia. b

Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt.

Abstract PVA/ZnS nano-composites were prepared by both thermolysis and casting procedures. The influence of annealing temperature of ZnS nano filler on the structure properties of composite films was studied by x-ray diffraction technique and Fourier transform infrared (FTIR) techniques. X-ray analysis revealed that ZnS can be obtained with changing the annealing temperature up to 500 oC, above this temperature ZnS converted into ZnO. Moreover, the crystallite size of ZnS increased from 4 nm to 10 nm as the annealing temperature rose from 300 to 500 oC. The effect of crystallite size of nano filler on extinction coefficient, refractive index, band gap, dielectric constant, single-oscillator and the dispersion energies was studied in details using UV–vis. spectrophotometer technique. The photoluminescence technique (PL) showed that, PVA/annealed ZnS nano-composite films exhibited five sub-emissions spectra for ZnS annealed at 300°C and 400 oC while the sample contained ZnS annealed at 500 oC displayed two sub-emissions. PL intensity enhanced with increasing the crystallite size of ZnS nano particles.

Keywords: annealed; ZnS; PVA; size; structure; optical. *Corresponding

Author: M.H. Abdel-Kader ([email protected] ).

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Introduction The study of novel polymer nano-composite materials contain semiconductor nano-crystals has attracted widespread scientific and industrial interests because of their size-dependent characteristics [1]. The possible applications of the nano-composites based on polymer were in optoelectronics, aerospace, automotive [2]. The low-priced and diversity of polymer materials make them very imperative hosts for nano particle materials [2]. Organic polymers frequently used as transparent optical systems because of their optical clarity and improved flexibilities, while their optical uses were limited because of its narrow refractive indices [3]. This limitation can be overcome by filling it with inorganic nano sized materials. Adding of nano materials to polymer permitted a deep enhancing for the properties of both polymeric and nano filler materials [3]. The electronic energy transformations between the polymeric matrix and inorganic nano fillers occur from the structural modification upon polymer and nano filler integrate [4]. The characteristics of polymer nano composites were found to be affected by various factors such as nano particles size, shape, amount, the interfacial bonding and spreading of the nano particles in the polymer medium [4]. Polyvinyl alcohol (PVA) polymer is widely used on a large scale of applications due to its high dielectric constant, excellent charge storage capacity, low electrical conductivity, high flexibility, and high transparency [5]. In addition, PVA contains carbon chain backbone with hydroxyl groups (OH) connected with methane. These OH groups are the source of hydrogen bonding and therefore help in the creation of polymer composite [6]. Additionally, PVA is a nontoxic, water-soluble and easy film-forming ability [7]. The broad range of uses of PVA could be increased through integration of nano dopant into PVA environment. Zinc sulfide (ZnS) nano particles is one of the most important group II–VI semiconductor filler with a large band gap (Eg) of about 3.7 eV at ambient temperature with numerous outstanding chemical and physical properties [8]. The change in crystallite size can be performed either by changing the method of preparation or changing the annealing temperatures [9, 10]. Guruswamy et al. [11] found that the energy gap of PVA decreased as it doped with ZnS but its thermal stability was enhanced as the amount of ZnS increased in polymer matrix. Tiwari et al. [12] investigated the optical properties of nano-composites based on ZnS and different polymers; poly(vinyl alcohol), starch and hydroxypropylmethyl cellulose. They found that the PL emission intensity changes with the nature of capping agent. The intense and broad survey in the literature indicated a nearly very little or absolutely rare work has been performed to study the variations in the band gap values with the annealing temperature (or the particle size) of the doped ZnS nano particles. So the novelty comes from introducing a new method for controlling the variations in the band gap values (increasing it) in a promising way that suits the composite material under study for manufacturing of highly transmission electronic devices in the visible range. This of course after investigation of a proper annealing temperature for the preparation of ZnS nano particles as a single phase structure by thermolysis procedure. The structural and optical characteristics of annealed ZnS/PVA nano-composites were studied by x-ray diffraction (XRD), Fourier transform infrared (FTIR), UV spectroscopy and photoluminescence (PL) techniques. 2. Experimental Nano ZnS were prepared using thermolysis procedure by mixing, grounding and heating a necessary amount of zinc acetates, and thiourea, obtained from Sigma-Aldrich at 300 ºC. The prepared sample divided into smaller parts and heated at 400, 500 ºC and 600 ºC (1h) in an electric oven, separately. At 600 oC, ZnS converted into ZnO phase, as will see in X-ray part, so

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this sample was avoided in the preparation of nano-composite films. The nano-composite films were formed by casting technique; (2 gm) PVA was dissolved in double distillated water (50 ml) via stirring it for 3h (90 oC). Only ZnS nano particles annealed up to 500 oC were added to PVA solution in weight ratio x (0.5 wt%) with respect to PVA based on the following: 𝑥(𝑤𝑡%) =

𝑤𝑓 𝑤𝑝 + 𝑤𝑓

x 100

where 𝑤𝑓 and 𝑤𝑝 are the weights of ZnS and PVA respectively. ZnS nano particles and PVA solution mixed together under strong stirring to avoid any agglomeration. Lastly, the mixtures were poured into Petri dishes and located in closed box for 3 days. A homogenous PVA/annealed ZnS nano-composite films with thickness of 400 µm were obtained. The x-ray diffraction were performed using (Shimadzu 6000 X-ray diffractometer, λ=1.5406 Å). UV–vis spectroscopy and photoluminescence investigations were performed by UV–vis. Spectrophotometer (Model Tomos UV-1800) and RF-1501 SHIMADZU, Ltd spectrophotometers, respectively. Fourier transform infrared (FTIR) spectroscopy (Bruker Tensor 27 FTIR Spectrometer) was used in the range of 400–4000 cm-1. 3. Results and discussion 3.1 Structural investigation X-ray diffraction data of ZnS samples annealed at different temperatures are given in Fig. 1a. As noticed from the figure ZnS has cubic structure up to 500 ºC, and then it converted into ZnO at 600 ºC. ZnS diffraction peaks are located at the Bragg angle (2θ in degree) values of 28.6, 47.5 and 56.8 that related to the (111), (220) and (311) Miller indices of ZnS with zinc-blend structure [JCPDS card No.05–0566]. On the other hand, ZnO has hexagonal structure with diffraction peaks located at 2θ=31.7, 34.3, 36.2, 47.5, 56.6 and 62.7o corresponding to the Miller indices (100), (002), (101), (102), (110) and (103), respectively. The diffraction pattern at 300 ºC exhibited broad peaks showing that the formed nano particle had a very tiny crystallite size. These peaks became narrower as the annealed temperature increased up to 500 oC as shown in Fig. 1b. The crystallite size of ZnS annealed at 300, 400 and 500 oC are 4, 7 and 10 nm, respectively, which was estimated using the following Scherrer equation: 𝐿=

𝐾

 𝑐𝑜𝑠

where  and β are the wavelength and half of maximal intensity, respectively. The x-ray diffraction data of pure PVA and annealed ZnS/PVA nano-composites are given in Fig. 1b. It is seen that the samples were characterized by main diffraction peak, noticed at 2θ=21°, which represented a partial crystallinity structure [13]. No difference could be detected between pure PVA and that loaded with ZnS, also no diffraction peaks emerge for ZnS phase. This indicates a homogenous distribution of nano ZnS over PVA matrix. FTIR studies provide a clear image about diverse intermolecular changes in the pure PVA and PVA/annealed ZnS nano-composites. The study includes gathering information about the interaction effects between different constituents within samples depending on the induced changes in the vibrational modes and the bands position. The FTIR spectra with the apparent

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bands in the wavenumber range between 500-4000 cm-1 are shown in Fig.2. For pure PVA a strong broad band appears in the wavenumber region (3156 cm-1- 3476 cm-1) centered at 3320 cm-1. This band assigned to the stretching vibration of O-H in the hydroxyl groups along the PVA polymer structure [14]. The two bands appear at 2937 cm-1 and 2825cm-1 are returned to the CH2 asymmetric and symmetric stretching respectively [15]. Other two bands at 1734 cm-1 and 1675 cm-1 are due to C=O and C=C stretching vibrations, respectively [14, 15]. The two bands were found at 1421 cm-1 and 1328 cm-1 are referred to CH3 bending vibration and CH2 stretching respectively [16]. The appearance of clear band at 1093 cm-1 assigned to the C-O stretching vibration and C–O–C groups in PVA, the band at 929 cm-1 is due to CH2 rocking vibration, the band at 835 cm-1 result from C-C stretching vibration while that at 671 cm-1 comes from the bending vibration of CH out of plane [17]. The bands specified in the region 500 - 640 cm-1 represents the stretching vibrations of Zn-S bond (exactly at 615 cm-1). These bands are also observed in annealed ZnS/PVA samples [18]. From the FTIR spectra, PVA/ZnS composite films spectra looks to a great extent similar to that of the pure PVA one. However, one can observe a slight small shift to the direction of lower wavenumber in the band position corresponding to the O-H stretching vibration and C-O stretching vibration of PVA. This represents an evidence for the interaction between hydroxyl groups along PVA structure and zinc cations reflecting the uniform distribution of the nanoparticles within polymer samples. A gradual variation in the bands peak intensity for composite films can be observed as an increase in the intensity when moving from 500 oC to 300 oC annealing temperatures as shown in the figure. Our results are consistent with the XRD result which indicates that, embedding ZnS nanoparticles annealed at different temperatures increases the degree of crystallinity of the polymer. 3.2 Optical properties The study of optical absorption spectra is a necessary tool for understanding the changes in the internal band structure of the material under test through gathering essential information about the optical band gap. All UV measurements of the samples were performed at room temperature. Studies showed that optical absorption procedure can be used for providing information about both optically induced transitions and band structure for materials under study [19]. The absorbance and transmittance spectra in the region 200-1000 nm for pure PVA and PVA /annealed ZnS nano-composites are shown in Fig.3. A wide absorption band with faint intensity in the UV region 220–280 nm with a spectral peak of maximum around 255 nm has been displayed for pure PVA. Similar results were observed although different nano-composite films based on PVA such as Al/PVA nano-composite [20], chitosan-Poly(vinyl alcohol) blend polymer nano-composites [21], Solid-polymer electrolytes PVA–LiClO4.3H2O[22], doped PVA films with nontoxic and environmentally friendly material [23] and PVA/Na2Dy2O4[24]. Other annealed PVA/ZnS samples prevails absorption peaks consistent with the pure ones. This wide band was returned to the transition (n ---- *) of the unshared electron pairs of both oxygen and carbon atoms in the C=C and C=O bonds which are present along the PVA structure and its tail head. Moreover, no absorption bands appeared in the visible spectrum range which reflects the high transparency of the pure PVA films used. Adding an amount of nano particle dopants to the polymer increases the absorption property across the entire spectral range. This increase in the absorbance reveals a gradual decrease in the transmittance spectra. This counter behavior for both absorbance and transmittance spectra is due to formation of new internal bonds (by attractive forces) between resulting zinc cations [ Zn2+] and hydroxide groups along the PVA backbone showing a change due to new defects responsible for disorders and generating stress in

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the intermolecular structure. The absorption spectra in the region (260-1000 nm) for all prepared samples decreases with increasing wavelength because of the decrease in the energy of the incident light [25]. Increasing the annealing temperature of the ZnS nano particles added to PVA polymer from 300 to 500 °C shows a decrease in the absorption property of all PVA/ZnS composites across the entire spectral range. This decrease corresponds to a gradual increase in the transmittance spectra. A possible interpretation for this behavior is that, increasing the annealing temperature of the added ZnS nano particles increases its particle size [26-31]. Larger particle size improves the internal structure by a process of adjustment that reduces the number of defects and disorders and causes stress relaxation. This complicates electronic transitions within band gap region. The rise in the transmittance spectra with annealing temperature reflects the role of the particle size in scattering of the incident beam either by volume or surface scattering [31]. Optical parameters such as refractive index n and extinction coefficient k within a certain range of wavelengths are essential criteria when directing the new PVA/ZnS composite films for particular applications. Refractive index n and the extinction coefficient k are related to each other by the following relation [32-34]: 𝑛=

4𝑅 1+𝑅 + ― 𝐾2 1―𝑅 (1 ― 𝑅)2 K=

 2

where  and  are the absorption coefficient and wavelength, respectively. The absorption coefficient α (λ) can be determined from the experimental results of the absorption spectra using the following relation:

 () =

( )

2.303 𝐴 𝑑

where d and A are the film thickness the absorbance, respectively. The extinction coefficient k plays an important role for giving clear description about the medium absorption properties when affected by light of a certain wavelength. It reflects the absorption alterations within the internal structure of the medium when electromagnetic light waves pass through it. Fig.4a represents the extinction coefficient for PVA and PVA/annealed ZnS samples. The spectra have peaks consistent with these obtained in absorbance spectra at 255 nm. It is clear from the figure that firstly, the extinction coefficient increases with the addition of ZnS nano particles at 300 °C and then it decreases with the rise in the annealing temperature, these results are completely agreed with those obtained Fig.3a. A possible explanation for this is that with increasing the annealing temperature, the fraction of incident electromagnetic energy lost by absorption decreases due to increasing the probability of scattering [35]. One can see from Fig.4b that the refractive index increases for PVA/ZnS annealed at 300 °C and then it decreases with the addition of more annealed nano fillers. It is remarkable that the refractive

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index spectra exhibit wide dispersion peaks in the low wavelengths region while almost plateau in the high one. The refractive index is one of the most fundamental optical parameters of a material that was used for supplying deep information about the electronic polarizability of different molecules which means it reflects the polarization action that happens under the effect of the electromagnetic field of the incident beam of light. It also supplies information about the intermolecular interactions and about the local field inside the medium. The wide dispersion region appeared at low wavelengths range is returned to the polarizability effect that happened to the samples molecules under the effect of the applied electromagnetic field while in the high wavelengths region samples molecules don't obey to the electromagnetic field alternations because of their inertia [36]. The dependence of refractive index on both density and polarizability can be understood more clearly from Lorentz–Lorenz relation [37]: 𝑛2 ― 1 4𝜋𝑁𝑚𝜌𝛼 = 𝑛2 + 2 3 𝑀𝑊 where is n, Nm, MW, α and ρ are refractive index, Avogadro’s number, molecular weight, polarizability and density, respectively. Therefore, the decrease in the refractive index samples with increasing the annealing temperature of added nano fillers can be returned to the effect of the particle size on varying the intermolecular structure by reducing the hydrogen bonds formed between ZnS nano particles and the OH groups along the PVA backbone that results in an increase between inter-atomic spacing and thus the composite films become less stressed showing a reduction in the density of the films. The investigation of optical absorption spectra is an essential parameter for having information about band gap structure of the material. In general, materials (semiconductors or insulators) can be classified into two main types according to the band gap; direct and indirect band gaps materials. The transition from valence band to conduction band in indirect band gap materials depends on the proper phonon of the right magnitude of crystal momentum. In indirect band gap materials, the bottom of the conduction band does not correspond to zero crystal momentum while in direct band gap materials the top part of valence band and the bottom of the conduction band are both positioned at the same zero crystal momentum (wave vector) [19, 38]. Others investigated that near the fundamental band edge both direct and indirect transitions can occur [39]. Both direct and indirect transitions can be displayed by plotting relations between (ℎ)2 and (ℎ)1/2 with the photon energy (ℎ), respectively according to the following relation between absorption coefficient  and incident photon energy (ℎ): 𝑛

ℎ = 𝐴(ℎ ― 𝐸𝑔)

where A, 𝐸𝑔 and n are a constant, the optical band gap energy of the material and an indicator depends the type of transition, respectively. n take values 1/2, 2, 3/2 and 3 depending on the type electronic transition: the allowed direct, allowed indirect, forbidden direct and forbidden indirect transitions, respectively [38, 40]. Fig. 5 shows the spectral distribution for the variations of both (ℎ)2 and (ℎ)1/2 with the photon energy (ℎ) for direct and indirect transitions. The interception of the linear parts of

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curves (ℎ)2 and (ℎ)1/2 with the photon energy (ℎ) axis represents the exact values for the energy gap 𝐸𝑔 as shown in table 1. It is clear from the figure that the shape of the absorption edge attitude is the same for all annealing temperatures and there is a shift in the absorption curve (PVA/ZnS annealed at 300 °C) towards the lower energy side and then as the annealing temperature increases the shift moves towards the higher energy side. A possible explanation for the first behavior is that introducing nano fillers into a polymer matrix reduces the band gap and this reduction in the band gap reflects the rise in the degree of disordering in the composite films due to the variations in its intermolecular structure. This is a clear evidence of the formation of some defects which are responsible for producing localized states in the optical band gap region. the increase in the energy gap values from 3.3 or 2.3 eV (for direct or indirect transition for sample contains ZnS annealed at 300 °C) to 4.9 or 4.7 eV (for direct or indirect transition for sample contains ZnS annealed at 500 °C) is returned to the vital role of the particle size for producing an enhancement in the band gap structure via a decrease in the number of defects and hence the number localized states. The dispersion spectral data of the refractive index n at energy value less than that of the absorption edge can be efficiently resolved using the single oscillator approximation model proposed by Wemple and DiDomenico [41]. In this model both the single-oscillator energy 𝐸𝑜 and the dispersion energy 𝐸𝑑 parameters are related to the refractive index n by the following empirical formula [36, 41, 42]: (𝑛2 ― 1) =

𝐸𝑜𝐸𝑑 2

𝐸2𝑜 ― (ℎ) 𝐸𝑑 determines the strength of interband optical transitions and it is closely related to the effective number of charge distribution (valence electrons) per anion. Experimentally it was found that 𝐸𝑑 doesn't depend to a great extent on either the band gap value or the valence electrons volume density [41] while 𝐸𝑜 is provides deep insights into the optical properties of the material and it is closely related to the energy gap value by the empirical relation (𝐸𝑜1.3 𝐸𝑔) which agrees quite -1 well with the single oscillator model. Fig. 6 represents the relation between the (𝑛2 - 1) and the square value of the photon energy (ℎ)2, the values of the 𝐸𝑑 and 𝐸𝑜can -1

be calculated from the slope (𝑠𝑙𝑜𝑝𝑒 = 𝐸𝑜𝐸𝑑) and the interception point on the vertical axis ( 𝐸𝑜

𝑖𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡 = 𝐸𝑑). The calculated values of 𝐸𝑑 and 𝐸𝑜are shown in table 1. Since 𝐸𝑜 is closely related to the energy gap according to mentioned empirical relation this means that it follows the compositional variations in the band gap region. The decrease in the oscillator energy values at annealing temperature 300 °C is a clear evidence of appearance of new localized states associated with the addition of ZnS nano particles where this result agrees with that of the energy gap when decreased from 5.3 eV (for pure PVA) to 3.3 eV (PVA with ZnS annealed at 300 °C) and the further increase in 𝐸𝑔 values is consistent with the increase in 𝐸𝑜 values with the annealing temperature as shown in table 1. This means that the rise in the 𝐸𝑜 values is associated to reduction in the degree of disordering due to particle size effect. Since 𝐸𝑑 measures the interband optical transitions strength and it clearly depends on the effective number of valence electrons, the gradual decrease in the dispersion energy 𝐸𝑑 values with increasing the annealing

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temperature of impeded ZnS inside the PVA matrix proves that there is a decline in the effective number of valence electrons necessary for transitions upon receiving energy meaning that the probability of forming new bonds between the added nano particles and the PVA polymer will be less which in turn reduces the number of charge transfer complexes between PVA molecules and the ZnS nano particles and hence the number of defects will be declined and disorders as well. This behavior enhances the energy gap values with annealing temperature as indicated in table 1. Depending on the calculated values of both the refractive index n and the extinction coefficient k, one can easily determine the complex dielectric constant (𝜀 = 𝜀𝑟 + 𝑖𝜀𝑖) where 𝜀𝑟 is the real part of the dielectric constant and 𝜀𝑖 is the imaginary part. Both are related to n and k by the following relations [43, 44]: 𝜀𝑖 = 2𝑛𝑘 𝜀𝑟 = 𝑛2 ― 𝑘2 𝜀𝑟 normally gives clear image about the dispersion in the medium while 𝜀𝑖 provides information about the incident electromagnetic wave energy dissipation in the medium. In the field of industrial applications, usually the dispersion parameter has a great role in the designing process of optical devices particularly in the optical communication field. Fig.7 represents the real and imaginary parts of the dielectric constant of pure PVA films and PVA doped with ZnS nano particles annealed at different temperatures as a function of wavelength. It is clear from the figure that the spectra of 𝜀𝑟 decreases with increasing the wavelength and beyond the absorption edge value it slightly tends to have a constant behavior. Upon doping pure PVA samples with ZnS nano particles (annealed at 300 °C) a rise in the value of 𝜀𝑟 has been observed which reflects the role of the new hydrogen bonds formed between zinc cations [Zn2+] and hydroxide groups in increasing the number of defects and disorders resulting in an increment in the number of density of states and hence the number of accumulated space charge regions increase. The decrease in the 𝜀𝑟 value with the increased the annealing temperature of ZnS filler can be attributed to the role of the particle size in suppressing the formation of hydrogen bonds and these results in a rise between inter-atomic spacing causing stress relaxation. This reduces the number of accumulated space charge regions and thus a lower value of 𝜀𝑟 is obtained [45]. The shape of the εi spectra for all composite films looks have the same tendency beyond the absorption edge value; the spectra increases slightly in a linear manner with increasing the wavelength. It is noticeable that the deviation increases more upward with the rise in the annealing temperature of the ZnS nano dopants. An increment in the εi values at small values of wavelength (below 350 nm) to a certain maximum can be observed which reflects the domination effect of the extinction coefficient. The resemblance in the spectral shape of both εi and extinction coefficient k was expected because of the direct proportional relationship. The εi spectral behavior with the annealing temperature is similar to that of 𝜀𝑟 which indicates that polymer films doped with more annealed nanoparticles dissipate electromagnetic wave energy more that those of less annealed ones due to the particle size effect. 3.1 Photoluminescence emission analysis (PL)

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Fig.8 reveals a photoluminescence (PL) emission for all nano-composites measured from 300500 nm under an excitation of 260 nm. As seen from the figure, the PL emission of the PVA/ annealed ZnS nano-composites materials exhibited five emission peaks for the nano-composite with ZnS annealed at 300 oC; one in UV, and four in visible region (two violets and two blue). The PVA/ annealed ZnS at 400 oC exhibited also five emission peaks; two in UV, one in violet and two in blue regions. The sample contains ZnS annealed at 500 oC exhibited one main broad peak, which can decomposed using Gaussian fitting into two sub peaks in UV and violet regions. The PL intensity enhanced as the annealing temperature of ZnS doped nano composite increased. This enhancement can be explained by decreasing the defect concentration and improving crystal quality as the annealing temperature of ZnS increased. The PL peaks shifted towards a red region as ZnS annealing temperature in nano-composite increased, due to increase of crystallite size. Shahi et al. [46] observed five emissions out from ZnS/PVA in UV, blue and green regions. UV peak attributed to the transitions involving interstitial zinc or sulfur atoms [47] while blue emission could be attributed as transitions from sulfur vacancy to different surface states [48]. 4. Conclusion X-ray diffraction study showed no difference in X-ray data of pure PVA and PVA/ZnS nanocomposites loaded with different annealed ZnS. Also FTIR analysis confirmed the existence of ZnS inside PVA matrix. Increasing the annealing temperature of the ZnS added to PVA revealed a decrease in the absorption and an increase in transmittance spectra of nano-composites. The extinction coefficient and refractive index increased with the addition of ZnS nano particles at 300 °C and then it decreased with rising of the annealing temperature. The energy gaps (direct and indirect), dielectric constant, single-oscillator energy (𝐸𝑜) first decreased as the PVA filled with ZnS annealed at 300 oC and then increased as the annealed temperature increased. The dispersion energy(𝐸𝑑) showed a contrary behavior. The variation of the dispersion parameter with annealing temperature is a promising result especially for designing and fabricating optical devices related to communication. PVA/annealed ZnS at 300 and 400 oC nano-composites exhibited five emissions in UV, violet and blue regions. While PVA/annealed ZnS at 500 oC revealed two emissions in UV and violet regions. The PL intensity enhanced as the annealing temperature of ZnS doped nano-composite due to decrease of the defect concentration. Also, The PL peaks shifted towards a red region as ZnS annealing temperature in nano-composite increased, due to increase of crystallite size. References [1] L. Chen,C.Wang, Q.Li,S.Yang, L.Hou, S.Chen, J.Mater.Sci.44, 3413 (2009) [2] H. Agrawal, K. Awasthi, V.K. Saraswat, Polym. Bull. 71, 1539 (2014) [3] D. K. Pradhan, R.N.P. Choudhary, B.K. Samantaray, Express Polym. Lett. 2, 630 (2008) [4] A.A.Alhazime, M.B. Mohamed, M.H. Abdel-Kader, J Inorg Organomet Polym (2018). https://doi.org/10.1007/s10904-018-1014-5 [5] B. Pradhan, K. Setyowati, H. Liu, D.H. Waldeck, J. Chen, Nano Lett. 8(4), 1142 (2008) [6] R. Singh, S.G. Kulkarni, N.H. Naik, Adv. Mater. Lett. 4, 82 (2013)

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[7] U. K. Parida, A.K. Nayak, B.K. Binhani, P.L. Nayak, J. Biomater. Nanobiotechnol. 2, 414 (2011) [8] A. R. Loukanov, C. D. Dushkin, K. I. Papazova, A. V. Kirov, M. V. Abrashev, E. Adach, Colloid Surface 245(1-3), 9 (2004) [9] M.B. Mohamed, M.H. Abdel-Kader, A.A. Alhazime, J.Q.M. Almarashi, J Mol Struct. 1155, 666(2018) [10] K. El-Sayed, M.B. Mohamed, S. Hamdy, S.S. Ata-Allah, J Magn Magn Mater. 423, 291(2017) [11] B. Guruswamy, V. Ravindrachary, C. Shruthi, R. N. Sagar, S. Hegde, AIP Conf Proc. 1953 030211 (2018) [12] A. Tiwari, S. A. Khan, R. S. Kher, S. J. Dhoble and A. L. S. Chandel, Luminescence 31, 428 (2016). [13] T. Sangappa, S. Mahadevaih, S. Divakar, M. Pattabi, R. Somashekar, Nucl. Instr. Meth. Phy. Res. B 266, 3975 (2008). [14] Omed Gh. Abdullah, Yahya A. K. Salman, Salwan A. Saleem. J Mater Sci: Mater Electron. 27, 4, (2016). [15] Aashis S. Roy, Satyajit Gupta, S. Sindhu, Ameena Parveen, Praveen C. Ramamurthy, Compos B Eng. 47, (2013). [16] Omed gh. Abdullah and Salwan a. Saleem, J Electron Mater. 45, 11, (2016). [17] Kalim Deshmukh, M. Basheer Ahamed, R. R. Deshmukh, Pundlik R. Bhagat, S. K. Khadeer ,Pasha, Aditya Bhagat, Rutwesh Shirbhate, Fastin Telare and Chirag Lakhani, Polym Plast Technol Eng. 55, 3 (2016). [18] M. Kuppayee, G.K. Vanathi Nachiyar, V. Ramasamy, Mat. Sci. Semicon. Proc. 15, (2012). [19]S. B. Aziz, O. G. Abdullah, A. M. Hussein, R. T. Abdulwahid, M. A. Rasheed, H. M. Ahmed, S. W. Abdalqadir, A. R. Mohammed, J Mater Sci: Mater Electron. 28, 7473 (2017) [20] F. Naseri, D. Dorranian Opt Quant Electron. 49(4), 1 (2017) [21] S. B. Aziz, R. T. Abdulwahid, M. A. Rasheed, O. G. Abdullah, H. M. Ahmed, Polymers 9, 485 (2017) [22] M. Q. A. Al-Gunaid, Adel M. N. Saeed, Siddaramaiah, J. Appl. Polym. Sci. 135, 45852. (2018) [23] S. B. Aziz, J. Electron. Mater. 15, 4191 (2015).

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Intensity (a.u.)

(a)

o

600 C o

500 C o

400 C o

300 C

20

30

40

50

60

PVA/annealed ZnS o 300 C

(b)



2  

o

Intensity (a.u.)

400 C o

500 C PVA

10

20

30

40 

2  

50

60

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Fig.1. XRD diffractions for (a) annealed ZnS at different temperatures and (b) PVA and PVA/annealed ZnS nano-composites.

PVA/ZnS annealed at o

500 C

o

400 C

Transmittance (%)

o

300 C PVA

4000 3500 3000 2500 2000 1500 1000

500

-1

Wavenumber (cm )

Fig.2. FTIR for PVA and PVA/ZnS nano-composites.

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pva PVA/ZnS annealed at o 300 C o 400 C o 500 C

Absorbanc (a.u.)

(a)

200

400

600

800

1000

(nm)

60

(b)

Transmittance (%)

50 40 30 20 10 0 200

400

600 (nm)

800

1000

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Fig.3. UV-visible (a) absorbance and (b) transmittance spectra of PVA and PVA/ZnS nano-composites.

(a)

k (extinction Coefficient)*10

-2

0.24

PVA PVA/ZnS annealed at o o 300 C 400 C o 500 C

0.16

0.08

0.00 200

300

400

500

600

700

800

900

(nm)

Refractive index, n

2.4

(b)

2.2 2.0 1.8 1.6 300

400

500

600

700

800

900

(nm)

Fig.4. wavelength dependent of (a) extinction coefficient and (b) refractive index for PVA and annealed ZnS/PVA nano-composites.

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2000

h)

2

PVA PVA/ZnS annealed at o 300 C o 1500 400 C o 500 C

1000

500

0

(a)

0

1

2

3

4

5

6

h (eV)

6

h)

0.5

5 4

(b)

3 2 1 0

5.8 eV

2.3 eV

0

1

2

3 4 h (eV)

5

6

7

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Fig.5. Relationship between (a) (h)2, and (b) (h)0.5 against (h) for PVA and annealed ZnS/PVA. nanocopmpsites.

0.52 0.48

2

(n -1)

-1

0.44

PVA PVA/ZnS annealed at o 300 C o 400 C o 500 C

0.40 0.36 0.32 5

6

7 2 (h (eV)

8

9



Fig.6. Plot of (n2 - 1)-1 against (h)2 for PVA and annealed ZnS/PVA nano-composites.

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6

PVA PVA/ZnS annealed at o 300 C o 400 C o 500 C

(a)

r

5

4

3

2 300

400

500

600

700

800

900

1000

800

900

1000

(nm)

1.0

(b)

0.8

i

0.6 0.4 0.2 0.0 300

400

500

600

700

(nm)

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Fig.7. wavelength dependent of (a) real part of dielectric constant and (b) dielectric loss for PVA and annealed ZnS/PVA nano-composites.

0.8 0.6

347 nm

60 396 nm 408 nm

0.4

50

0.2 0.0

330

360

390

420

450

40

480

352 nm

464 nm

446 nm

330

360

390

420

450

480

(nm)

(nm)

160

o

300 C

70 PL(a.u.)

Normalized PL(a.u.)

80

PVA/ZnS annealed at o 300 C o 400 C o 500 C

1.0

363 nm

365 nm

o

400 C

o

500 C

600

404 nm

120

464 nm

80

330

360

390

420

(nm)

450

400

405 nm

200

447 nm

100

PL(a.u.)

PL(a.u.)

140

480

0

330

360

390 (nm)

420

450

480

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Fig.8. PL spectra at excitation of 260 nm for PVA and annealed ZnS/PVA nano-composites.

Table 1. Energy gaps and dispersions parameters for PVA and annealed ZnS/PVA nano-composites. Direct band gap energy Eg (eV) PVA 5.3 PVA/ZnS annealed at 300 oC 3.3 o 400 C 4.4 500 oC 4.9

Indirect band gap energy Eg (eV) 5.8 2.3 3 4.7

Eo (eV)

Ed (eV)

6.9

9.9

5.3 5.6 6.1

14 13.7 12

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CONFIRMATION OF AUTHORSHIP TITLE: Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite We, the undersigned, confirm that we are the joint authors of the above paper. We confirm that all the authors have had material input into the submission. We confirm that, to our knowledge, all the claims, statements and conclusions are true and are our jointly held opinions. We confirm that we all accept the terms of publication of the publisher. Author names: Mohamed Bakr Mohamed M.H. Abdel-Kader

Journal Pre-proof Manuscript title:

Effect of annealed ZnS nanoparticles on the structural and optical properties of PVA polymer nanocomposite

The authors whose names are listed immediately below certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Author names: Mohamed Bakr Mohamed M.H. Abdel-Kader