Physical, structural and optical properties of bio-silica borotellurite glass system doped with samarium oxide nanoparticles

Physical, structural and optical properties of bio-silica borotellurite glass system doped with samarium oxide nanoparticles

Journal of Non-Crystalline Solids 529 (2020) 119777 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: ww...

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Journal of Non-Crystalline Solids 529 (2020) 119777

Contents lists available at ScienceDirect

Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol

Physical, structural and optical properties of bio-silica borotellurite glass system doped with samarium oxide nanoparticles

T



A.S. Asyikin, M.K. Halimah , A.A. Latif, M.F. Faznny, S.N. Nazrin Glass and Dielectric Laboratory, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

A R T I C LE I N FO

A B S T R A C T

Keywords: Rice husk Borotellurite glasses Samarium oxide nanoparticles Optical band gap Polarizability Metallization criterion

Glasses with chemical composition {[(TeO₂)0.7 (B₂O₃)0.3]0.8 [SiO₂]0.2}1-x {Sm₂O₃ NPs}x where x = 0.01 to 0.05 molar fraction have been fabricated using conventional melt-quenching method. Fourier transform infrared (FTIR) spectra reveal the presence of TeO3, SiO2 and BO3 structural units in the glass network. The existence of samarium oxide nanoparticles was recorded through high resolution transmission electron microscopy (HRTEM) with particle size of 71.74 nm. Meanwhile, the optical properties of fabricated samples were determined by UV–vis analysis. The variation in the optical band gap identifies the modification in the glass network to the formation of bridging oxygen (BO) and non-bridging oxygen (NBO). Other optical parameter including refractive index, Urbach energy, electronic polarizability, oxide ion polarizability and optical basicity were determined. The metallization criterion values obtained is in the range of 0.403 to 0.409, which suggest that the glass material has a huge potential applications, in non-linear optics fields.

1. Introduction The extending interest on optical properties of trivalent rare earth ions doped silicate, borate and tellurite glass are investigated by many researchers due its technological and commercial application in fiber optics, sensors, optoelectronics, solid state lasers and waveguide laser [1–4]. Tellurite glass is selected as the best host material due to its attractive properties such as excellent thermal stability, low phonon energy, low melting temperature and high linear and nonlinear refractive index [5–9]. Since tellurium dioxide is a conditional glass former, it requires the addition of another substance, such as another glass former and network modifier to form a progressively steady glass [10–11]. Borate glass are fusible, chemical durability, high transparency and good solubility of rare earth oxides, and these properties make the borate glass known as a standout amongst other glass former [12]. The addition of TeO2 in borate glasses decreases the hygroscopic nature of the glass matrix and the combination of these components in one glass system promote the quality and improve the stability of the glass [10,13]. Besides, the properties of borotellurite glass are enhanced by adding silica extracted from waste rice husk. Silica usually provides mechanical strength to the glass [14]. Lanthanides oxide nanoparticles are one of the elements that are applicable to be incorporated into the glass system as dopant due to the interesting properties especially in the optical and electronic



applications [15]. The introduction of nanoparticles shows specific effect toward the optical properties of glass material due to the size dependence of the particle. Samarium oxide nanoparticles doped glasses are observed for the effect of particle size, quantum confinement effects, interfacial effects and interfacial effects [16]. In view of previous research, there is a huge gap of research by scientist on the effect of incorporation of samarium oxide nanoparticles into glass system. Therefore, this research was set forth to investigate the structural and physical properties of bio-silica borotellurite glass doped with samarium oxide nanoparticles. The optical properties of this glass also been observed for the optical band gap, Urbach energy, refractive index, electronic polarizability, oxide ion polarizability, optical basicity and metallization criterion. 2. Experimental procedure 2.1. Extraction of silica from waste rice husk In this study, the silica that was included in the glass composition was obtained from the waste rice husk. Rice husk was washed with distilled water to get rid of the contaminants and dust. The water-rinsed rice husk were mixed with 2 M of hydrochloric acid (HCl) and heated at 110 °C for 3 h. The solution was filtered and rice husk was washed with distilled water several times to remove excess acid that may remain in

Corresponding author. E-mail addresses: [email protected] (M.K. Halimah), [email protected] (A.A. Latif), [email protected] (S.N. Nazrin).

https://doi.org/10.1016/j.jnoncrysol.2019.119777 Received 2 August 2019; Received in revised form 29 October 2019; Accepted 10 November 2019 0022-3093/ © 2019 Elsevier B.V. All rights reserved.

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using CuKα radiation, with an uncertainty of 2θ ˂ 1.5% and the data obtained were transferred to a computer that was connected to the xray diffractometer. Next, the functional groups that exist in the glass samples were identified through FTIR spectroscopy. FTIR spectra were obtained in the range of 280–4000 cm−1 by using Perkin Elmer FTIR Spectrophotometer with an uncertainty of ± 10 cm−1. The existence of samarium oxide nanoparticles in the glass was captured using High Resolution Transmission Electron Microscope (HRTEM) JEOL JSM–IT-100 with an accelerating voltage of 200 kV. Fine powder form of glass samples underwent sample preparation process before being viewed under HR-TEM. The sample preparation process start with mixing the glass samples with acetone solution and the mixture was sonicated for about 30 min to ensure uniform dispersion of the samples in the acetone solution. Then, a drop of the solution was placed on the centre of carbon grids, left to dry under room temperature and transferred on the sample holder of the instrument. The scanning process was controlled by the computer connected to the instrument to obtain the HR-TEM image of the nanoparticles in the glass sample. The instrument that will be used for the optical absorption measurement is UV-1650PC UV–Vis Spectrophotometer (Shimadzu). The glass sample underwent characterization process under room temperature and the optical absorption data were acquired for wavelength in the range of 220–2000 nm with the uncertainty of ± 0.3 nm. In addition, the physical properties of the glass were determined through the density and molar volume of the fabricated glass samples. In this study, the density of the bulk form glass sample was measured at room temperature based on Archimedes’ principle by using distilled water as immersion liquid. The molar volume of the glass was calculated based on the density of the glass samples and molecular weight of the element. Table 2 shows the uncertainties of the devices being used for each measurement in this work.

Table 1 Mass composition in 13 g samples. Molar fraction, x

Weight of TeO₂ ( ± 0.0001 g)

Weight of B₂O₃ ( ± 0.0001 g)

Weight of SiO₂ ( ± 0.0001 g)

Weight of Sm₂O₃ nanoparticles ( ± 0.0001 g)

Total (g)

0.01 0.02 0.03 0.04 0.05

9.5531 9.2789 9.0148 8.7603 8.5148

1.7860 1.7347 1.6853 1.6377 1.5918

1.2844 1.2476 1.2121 1.1778 1.1448

0.3765 0.7389 1.0878 1.4242 1.7485

13 13 13 13 13

the rice husk. Next, the rice husk was dried in the oven for 30 min at 110 °C. Then, the rice husk was put in alumina crucible and burned in the furnace at 700 °C for 2 h to obtain the white rice husk ash known as silica. 2.2. Glass fabrication A series of bio-silica borotellurite glass doped with samarium oxide nanoparticles with a chemical composition of {[(TeO₂)0.7 (B₂O₃)0.3]0.8 [SiO₂]0.2}1-x {Sm₂O₃ NPs}x where x = 0.01, 0.02, 0.03, 0.04 and 0.05 molar fraction were synthesized using a method known as melt quenching. The starting material to produce this glass samples are silica, SiO2 synthesized from waste rice husk and commercially chemical powder of boron oxide, B2O3 (98.5%, Alfa Aesar), tellurium (IV) oxide, TeO₂ (99.99%, Alfa Aesar) and samarium oxide nanoparticles, Sm2O3 NPs (99.99%, Nanostructured & Amorphous Materials Inc). The raw materials were weighed using an electronic balance according to the required amount, as shown in Table 1. Then, the weighed element (13 g) was placed in an alumina crucible and stirred using a glass rod for 30 min to ensure the mixture is homogenous. The alumina crucible containing 13 g of chemical powder was transferred to the first furnace to undergo pre-heating process for 1 h at 400 °C. This step was conducted to eliminate water molecule that might present in the mixture. Next, the alumina crucible was put into the second furnace to proceed with melting process for 3 h at 1050 °C. In the meantime, a stainless steel cylindrical shape mould was cleaned to remove dirt and impurities that may stick on it. The mould was also pre-heated at 400 °C using the first furnace to prevent thermal shock from occurring during the quenching step due to the differences in temperature between the melt and mould. After melting process, the melt was quenched rapidly into the mould to avoid solidification from taking place. Lastly, the mould that contains the melt mixture was annealed in the first furnace for 2 h at 400 °C. The furnace was switched off and the samples were left to cool down for one day. The glass samples were polished on both sides using different kinds of silicon carbide (SiC) sand paper (400 mesh, 800 mesh, 1200 mesh, 1500 mesh) to obtain transparent, flat and parallel surface. The thickness of the glass samples was measured using a digital vernier caliper and all the glass samples possess the thickness required for optical measurement which is around 2.20–2.30 mm. The polished glass samples were subjected to various characterization technique to investigate the physical, structural and optical properties.

3. Result and discussion 3.1. X-ray fluorescence (XRF) analysis XRF spectroscopy was used to examine the chemical composition in the rice husk ash. Table 3 shows the result from XRF analysis for the composition in the extracted silica. From Table 3, the presence of silica was detected in the composition with highest percentage which is 98.130%. The other elements that appeared in the rice husk ash with small amount is seen as impurities. An extracted silica with purity of 98.13% is considered as a high purity when compared to some other research [17]. The chances of the inhomogeneous to exist as nanoparticles is fairly small since the nanosize impurity will usually exist in crystalline form that will appear as Bragg peaks in the XRD. The presence of nanoparticles as observed in HRTEM image has also been reported by other researchers such as Azlan et al. [25] and Hazlin et al. [13] with glass samples that did not have silica in their respective glass composition. Therefore, it can be concluded that the existence of nanoparticles are not originated from silica or from its impurities [13,25]. The purity of silica synthesized from waste rice husk in this study is found to be as close as reported by other literature [18]. The silica content from silica extraction process were affected by many factors such as temperature of incineration, incineration time and concentration of hydrochloric acid [19].

2.3. Glass characterization The elemental analysis to verify the purity of silica in the rice husk ash was performed using X-ray fluorescence (XRF) (Shimadzu, EDX720) spectrometer. Some of the glass samples were crushed using a plunger and ground using a pestle and mortar to make it available in fine powder form for structural testing including X-ray diffraction (XRD), Fourier transform infrared (FTIR) and high resolution transmission electron microscopy (HR-TEM). XRD patterns of the prepared glass were determined using X′Pert PRO Panalytical Philips in order to prove the amorphous nature of the glass. The glass samples were scanned at room temperature for 5 min in the angle of 20°≤ θ ≤ 80°,

Table 2 Uncertainties for each measurement in this work.

2

Measurement

Uncertainties

X-ray Diffraction (XRD) Fourier Transform Infrared (FTIR) High Resolution Transmission Electron Microscope (HR-TEM) UV–Vis Spectrophotometer Density

2θ ˂ 1.5% ± 10 cm−1 ± 0.02 nm ± 0.3 nm ± 0.001 g/cm3

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Table 3 The chemical composition in the rice husk ash. Composition SiO2 SO3 K2 O Fe2O3 ZnO CaO MnO PtO2 Cr2O3

Percentage (%) 98.130 0.602 0.290 0.257 0.227 0.194 0.106 0.099 0.095

Fig. 3. HR-TEM image for samarium oxide nanoparticles doped bio-silica borotellurite glasses at 0.03 molar fraction.

wavenumber ranges from 651–667, 1050–1060, 1225–1233 and 1369–1378 cm−1. The first band detected at 651–667 cm−1 is attributed to the Te–O vibration in trigonal pyramid, TeO3 groups [21]. The absorption at 651–667 cm−1 is slightly shifted to the higher wavenumber as the concentration of Sm2O3 NPs increase which suggests the increasing concentration of TeO3 units. The peak observed at 1050–1060 cm−1 is related to the asymmetric stretching vibration of Si–O–Si bonds [22]. The absorption bands for borate network are active in the wavenumber of 1225–1233 and 1369–1378 cm−1 which corresponded to the trigonal B–O bond stretching vibrations of BO3 units from boroxyl groups [23] and asymmetric stretching vibrations of the BO3 triangles in metaborate, pyroborate and ortho-borate units [24].

Fig. 1. XRD pattern for samarium oxide nanoparticles doped bio-silica borotellurite glasses (lines are drawn as guides to the eyes).

3.2. X-ray diffraction (XRD) analysis

3.4. High resolution transmission electron microscope (HR-TEM) analysis

Fig. 1 shows the XRD patterns for samarium oxide nanoparticles doped bio-silica borotellurite glass systems. All glass samples exhibit broad band at 20–30° angles and there is no presence of a sharp peak in the XRD spectra where it reveals the amorphous nature of the samples [20]. The XRD results confirm the feature of glass material has random and disorder arrangement.

High resolution transmission electron microscope (HR-TEM) technique was applied in order to demonstrate the presence of the nano-size particles after glass formation process [25]. Fig. 3 illustrates the distribution of samarium oxide nanoparticles in the glass system. The presence of samarium oxide nanoparticles is indicated as the black spot in the glass matrix. The average size of raw samarium oxide nanoparticles powder is around 15–30 nm [26], however the nanoparticles size increase to 71.74 nm after being incorporated in the glass system. The increase in nanoparticle size could be related to the agglomeration of samarium oxide nanoparticle in the glass matrix. This phenomenon could be explained through an Ostwald ripening process where small particles are dissolved and deposited onto larger particles [27]. The partial solubility of the nanoparticles can be seen through the difficulty in observing the nanoparticles throughout the glass sample by using HRTEM microscopy. This also indicates that the samarium oxide nanoparticles dissolves partially in the glass network.

3.3. Fourier Transform Infrared (FTIR) analysis Fourier Transform Infrared (FTIR) spectroscopy are used to investigate the structural modification that occurs in the glass system. The FTIR spectra for bio-silica borotellurite glass doped with samarium oxide nanoparticles is presented in Fig. 2. Fig. 2 depicts the FTIR spectra with the appearance of four absorption band in the

3.5. UV–Vis analysis The optical properties of the material could be explained in term of the interaction of the material with electromagnetic waves which are ultraviolet and visible light, particularly. The investigation of optical properties of samarium oxide nanoparticles doped bio-silica borotellurite glass was conducted by using UV–Vis spectroscopy. Fig. 4 shows the optical absorption spectra for samarium oxide nanoparticles doped bio-silica borotellurite glass recorded at room temperature with wavelength ranging from 220–1820 nm. All of the samples does not demonstrate the similarity of sharp fundamental absorption edge, which reveals the glassy state of the glass system [28]. There are several absorption bands observed in the UV–Vis spectra at 354, 404, 476, 958,

Fig. 2. FTIR spectra for samarium oxide nanoparticles doped bio-silica borotellurite glasses (lines are drawn as guides to the eyes). 3

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Fig. 5. Plot of (αћω)1/2 against photon energy, ħω for samarium oxide nanoparticles doped bio-silica borotellurite glasses (lines are drawn as guides to the eyes).

Fig. 4. UV–Vis spectra for samarium oxide nanoparticles doped bio-silica borotellurite glasses (lines are drawn as guides to the eyes).

1086, 1238, 1383, 1486, 1536, 1591 and 1649 nm which corresponds to transition from the ground state, 6H5/2 to excited state; 4D3/2, 4M19/2, 4 I11/2, 6F11/2, 6F9/2, 6F7/2, 6F5/2, 6F3/2, 6H15/2, 6F1/2 and 6H13/2. [29-32]. The optical band gap of the glass samples could be determined from the UV–Vis spectra. The optical absorption coefficient, α(ω) can be calculated using absorbance through the following equation [33]:

A (ω) = 2.303 ⎛ ⎞ ⎝d⎠

(1)

where A and d represent the absorbance and the thickness of the glass samples, respectively. The optical energy band gap values and Urbach energy can be determined by investigating the dependence of the absorption coefficient on photon energy. According to Mott and Davis theory, the relation between absorption coefficients with photon energy can be applied to determine the direct and indirect transition occurred in the band gap. The photon energy dependent absorption coefficient α(ω) is obtained by the following relation [34]:

α (ω) =

Fig. 6. Plot of (αћω)2 against photon energy, ħω for samarium oxide nanoparticles doped bio-silica borotellurite glasses (lines are drawn as guides to the eyes).

B (ℏω − Eopt )n (2)

ℏω

where B is band tailing parameter, ħω is the photon energy, Eopt is the optical energy band gap and n is an index that refer to the transition that occurred in the materials. The values of n equal to 2 for indirect allowed transition and ½ for direct allowed transition. In amorphous material, the optical band gap for indirect and direct transition can be obtained by using the Eqs. (3) and (4) respectively:

(α ℏω)1/2 = B(ℏω − Eopt)

(α ℏω)2

(3)

= B(ℏω − Eopt)

(4)

versus photon energy, ħω and (αħω) against A graph of (αħω) photon energy, ħω for samarium oxide nanoparticles doped bio- silica borotellurite glasses are plotted for indirect and direct transition according to Eqs. (3) and (4). The values for both optical band gap can be determined by extrapolating the linear region of ħω curve which being represented by the Tauc's plot [35]. The Tauc's plot of the glass system are shown in Figs. 5 and 6, respectively. The trend for the optical band gap of the glass samples are shown in Fig. 7, while its values are tabulated in Table 4. The optical band gap for indirect transition is in the range of 3.260 to 3.353 eV, meanwhile for direct transition is in the range of 3.356 to 3.405 eV. Although the variation in the energy band gap is small, the slight differences matters when the material is applied in some application such as optical fiber. A small variation in the energy band gap that directly contribute to small difference in the refractive index value is crucial for fibre drawing application because commonly 1/2

2

Fig. 7. Variation of optical band gap for indirect and direct transitions for samarium oxide nanoparticles doped bio-silica borotellurite glasses (lines are drawn as guides to the eyes).

Table 4 The values of optical band gap for indirect and direct transitions for samarium oxide nanoparticles doped bio-silica borotellurite glass with increasing concentration of samarium oxide nanoparticles.

4

Molar fraction, x

Indirect band gap ( ± 0.3 eV)

Direct band gap ( ± 0.3 eV)

0.01 0.02 0.03 0.04 0.05

3.304 3.353 3.284 3.276 3.260

3.381 3.405 3.371 3.364 3.356

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are in the range of 2.308 to 2.330.

the difference between the refractive index of the core and the cladding must be small to prevent loss of light signal. The size of particles could significantly influence the optical properties of material especially the energy band gap. The decrease in the particle size contributes to the increase in the optical band gap values. The optical band gap for indirect and direct transition exhibit an increasing trend as the concentration of samarium oxide nanoparticles increases. The introduction of samarium oxide nanoparticles up to 0.02 molar fraction into the SiO2–B2O3–TeO2 glass system might cause the movement of the electron to become restricted in the glass matrix due to the quantum confinement effect hence increasing the energy band gap [36]. However, the addition of dopant more than 0.02 molar fraction causing sudden decrement in optical band gap values. The variation in the optical band gap trend could be related to changes in the structure of the prepared samples with increasing concentration of samarium oxide nanoparticles [37]. According to Halimah et al. , the non-bridging oxygen is already present in the structure of tellurite group and the concentration of non-bridging oxygen increases as samarium oxide nanoparticles are included in the glass system [10]. The inclusion of samarium oxide nanoparticles as the network modifier will break the tellurite and borate structural unit and causing the formation of non-bridging oxygen in the glass matrix, hence, leading to a decrease in the optical band gap value.

3.7. Urbach energy Urbach energy provides information regarding the scale of disorder in the amorphous materials [40]. Materials that have large Urbach energy values will be more likely to convert weak bonds in the glass system into defects [10]. A graph of natural logarithm of the absorption coefficient, α(ω) against photon energy, ħω is plotted in order to determine the Urbach energy, ΔE. The values of ΔE were calculated by taking reciprocal of the slopes of linear portion of ln (α) against ћω curve by using the following equation [35]:

ℏω ⎞ α (ω) = B exp ⎛ ⎝ ΔE ⎠

where B is constant, ħω is the photon energy and ΔE is the Urbach energy. The cut-off position of the glass is very close to the absorption band of samarium as reported by Hussain et al. [9] as well as Maheshvaran et al. [41]. In this case, when samarium oxide nanoparticles are doped into silica borotellurite glass system, the actual cut off wavelength or fundamental absorption edge that have been considered might become too close until it basically overlap with samarium absorption band. This may also indicate that the wavelength for first absorption of photon that contribute to the excitation of the first electron to conduction band is extraordinarily near to the absorption for samarium element [9,41]. The Urbach energy values of bio-silica borotellurite glass doped with samarium oxide nanoparticles is shown in Fig. 9. The values fall in the range of 0.160 eV–0.204 eV. Shifting of absorption edge toward shorter wavelength cause higher optical band gap and lower Urbach energy. In this study, the increasing trend in Urbach energy values from 0.02 to 0.05 molar fraction indicate that the structure of the glass network becomes more disordered, less stable and might lead to a reduction in the glass compactness [42]. The increase in the Urbach energy with samarium oxide nanoparticles content confirms that the number of defects also increases. The increment in the Urbach energy also could be related to the conversion of TeO4 ↔ TeO3 and BO4 to ↔ BO3 units that contribute to the presence of NBO which lead to the weak connection of the glass structure [43]. Hence, the increasing values of Urbach energy with increasing concentration of dopant from 0.02 to 0.05 molar fraction shows that the fragility nature of the vitreous network to increase.

3.6. Refractive index Another important parameter in the optical properties of a material is the refractive index. The potential of glass materials to be utilized as optical devices could be determined by using the values of refractive index [38]. The refractive index value of each prepared glass sample is calculated from the optical band gap value by using the following equation [39]:

n2 − 1 =1− n2 + 2

Eopt 20

(6)

(5)

where n is the refractive index and Eopt is the optical band gap value for indirect transition of the glass samples. The refractive index values of the glass samples are plotted in Fig. 8. Based on the result, the refractive index for samarium oxide nanoparticles doped bio-silica borotellurite glass decreases from 0.01 to 0.02 molar fraction and increases with the further addition of samarium oxide nanoparticles to the glass systems. The number of non-bridging oxygen could affect the polarizability of the glass system which leads to the increase or decrease in the values for refractive index. The increasing amount of NBO atom that have large polarizability is responsible for the increment in the refractive index of the glass samples [10]. The values of the calculated refractive index of the glass samples

3.8. Other optical parameter Electronic polarizability gives information about the overall polarizability of the glass system meanwhile oxide ion polarizability reflect

Fig. 8. Refractive index for bio-silica borotellurite glass doped with samarium oxide nanoparticles with different molar fraction (lines are drawn as guides to the eyes).

Fig. 9. Urbach energy of bio-silica borotellurite glass doped with samarium oxide nanoparticles with different molar fraction (lines are drawn as guides to the eyes). 5

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Table 5 Electronic polarizability, oxide ion polarizability, optical basicity and metallization criterion of the bio-silica borotellurite glass doped with samarium oxide nanoparticles at different concentration of dopant. Molar fraction of Sm2O3 nanoparticles, x

Electronic polarizability, αm (Å3)

Oxide ion polarizability, αₒ²ˉ (Å3)

Optical basicity, ˄

Metallization criterion, M

0.01 0.02 0.03 0.04 0.05

7.2199 7.4829 8.1514 8.7078 9.3713

2.7939 2.8835 3.1517 3.3687 3.6313

1.0723 1.0908 1.1401 1.1743 1.2101

0.4064 0.4095 0.4052 0.4047 0.4037

on the polarizability of each element that is present in the glass matrix [44].The calculated values for electronic and oxide ion polarizability of samarium oxide nanoparticles doped bio-silica borotellurite glass are tabulated in Table 5. The values for both electronic polarizability and oxide ion polarizability increases with the increase in samarium oxide nanoparticles concentration. The substitution of Sm2O3 NPs into SiO2–B2O3–TeO2 glass system contribute to the structural changes from BO4 to BO3 units that causing the creation of non-bridging oxygens. Samarium ions consists of trivalent ions which have tendency to capture one electron from oxygen that leads to the formation of nonbridging oxygens. Non-bridging oxygen is more polarizable than bridging oxygen. Therefore, the high polarity of samarium ions leads to an increasing trend of the electronic and oxide ion polarizability of the glass system [8,45]. In addition, the trend for optical basicity and metallization criterion for bio-silica borotellurite glass doped with Sm2O3 NPs are depicted in Figs. 10 and 11, meanwhile the values are tabulated in Table 5. Optical basicity is the ability of the oxide ion to donate electrons to its surrounding cations. The values for optical basicity could be obtained based on the relation between oxide ion polarizability and optical basicity as proposed by Duff [38]:

1 ∧ = 1.67 ⎛1 − 2 − ⎞ α o ⎝ ⎠ ⎜

Fig. 11. Metallization criterion of bio-silica borotellurite glass doped with samarium oxide nanoparticles with different molar fraction (lines are drawn as guides to the eyes).

that the glass samples are metalizing and metallization criterion values close to 1 indicates the insulating behaviour of the prepared glass [39]. The values for metallization criterion, M could be calculated through this relation [24]:

M=1−

Rm Vm

(8)

where Rm is the molar refraction and Vm is the molar volume of the glass samples. The metallization criterion for samarium oxide nanoparticles doped bio-silica borotellurite glass is presented in Table 5. Based on Fig. 11, the metallization criterion increases from 0.01 to 0.02 molar fraction. However, the trend for the prepared glass suggest that the metallization tendency become high as the addition of Sm2O3 NPs exceed 0.02 molar fraction. According to Algarni et al., the decrease in metallization criterion values is attributed to the decrease in the optical band gap and the increase in the refractive index values of the glass samples [46]. The decreasing pattern for metallization criterion related to the large width of both valence and conduction band which subsequently contribute to the decrement in the optical energy band gap [47]. The reduction in the values of metallization criterion also indicates that the glass samples exhibit metallic behaviour. In addition, the metallization criterion values for this quaternary glass system is in the range of 0.403 to 0.409. Glass with metallization criterion values in the range of 0.30–0.45 is said to have a good non-linear optical properties [48]. This study found that the metallization criterion values of the glass samples fall in that range. Therefore, it could be proposed as a potential candidate for nonlinear optical application.



(7)

The relationship between oxide ion polarizability, αo2− and optical basicity, ∧ is directly proportional to each other as shown in Eq. (6). Therefore, the increasing values of the polarizability of oxide ion lead to the increasing trend of optical basicity of the glass system. The prediction about the metallic and non-metallic phenomena of a glass system can be determined by calculating the metallization criterion values. There are two conditions that tell about the nature of the glass system where the metallization criterion values less than 1 means

3.9. Density and molar volume Fig. 12 shows the density and molar volume for bio-silica borotellurite glass doped with samarium oxide nanoparticles. The addition of samarium oxide nanoparticles is found to gradually decrease the glass density from 3.928 g/cm3 to 3.273 g/cm3. This shows that the glass system becomes less compact as more dopant particles are added into the glass composition. Meanwhile, the molar volume of the glass system increases as the concentration of samarium oxide nanoparticles increases. The molar volume, Vm of the glass samples can be calculated based on the relationship between density and molar volume as shown below [49]:

Vm =

MW ρ

(9)

where MW is the molecular weight of the glass sample (g/mol) and ρ is the density of the glass sample (g/cm3). This equation shows that as the molar volume increase, the density

Fig. 10. Optical basicity of bio-silica borotellurite glass doped samarium oxide nanoparticles at different concentration of samarium oxide nanoparticles (lines are drawn as guides to the eyes). 6

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Acknowledgments The authors are thankful to the Glass and Dielectric Laboratory, Department of Physics, Universiti Putra Malaysia for providing the facilities during the research was conducted and also appreciate the financial support provided by Universiti Putra Malaysia under the grant GPB (9597200). References [1] I.Z. Hager, R. El-Mallawany, A. Bulou, Luminescence spectra and optical properties of TeO2–WO3–Li2O glasses doped with Nd, Sm and Er rare earth ions, Physica B 406 (4) (2011) 972–980. [2] A. Agarwal, I. Pal, S. Sanghi, M.P. Aggarwal, Judd–Ofelt parameters and radiative properties of Sm3+ ions doped zinc bismuth borate glasses, Opt. Mater. 32 (2) (2009) 339–344. [3] S. Peng, L. Wu, B. Wang, F. Yang, Y. Qi, Y. Zhou, Intense visible upconversion and energy transfer in Ho3+/Yb3+ codoped tellurite glasses for potential fiber laser, Opt. Fiber Technol. 22 (2015) 95–101. [4] P.R. Rao, G.M. Krishna, M.G. Brik, Y. Gandhi, N. 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Buddhudu, Absorption and emission analysis of RE3+ (Sm3+ and Dy3+): lithium boro tellurite glasses, J. Nanosci. Nanotechnol. 9 (6) (2009) 3672–3677. [10] M.K. Halimah, W.M. Daud, H.A.A. Sidek, A.W. Zaidan, A.S. Zainal, Optical properties of ternary tellurite glasses, Mater. Sci.-Poland 28 (1) (2010) 173–180. [11] V. Rajendran, N. Palanivelu, B.K. Chaudhuri, K. Goswami, Characterisation of semiconducting V2O5–Bi2O3–TeO2 glasses through ultrasonic measurements, J. Non Cryst. Solids 320 (1–3) (2003) 195–209. [12] S. Mahamuda, K. Swapna, M. Venkateswarlu, A.S. Rao, S. Shakya, G.V. Prakash, Spectral characterisation of Sm3+ ions doped Oxyfluoroborate glasses for visible orange luminescent applications, J. Lumin. 154 (2014) 410–424. [13] M.A. Hazlin, M.K. Halimah, F.D. Muhammad, Absorption and emission analysis of zinc borotellurite glass doped with dysprosium oxide nanoparticles for generation of white light, J. Lumin. 196 (2018) 498–503. [14] S.A. Umar, M.K. Halimah, K.T. Chan, A.A. Latif, Physical, structural and optical properties of erbium doped rice husk silicate borotellurite (Er-doped RHSBT) glasses, J. Non Cryst. Solids 472 (2017) 31–38. [15] R.J. Ellingson, M.C. Beard, J.C. Johnson, P. Yu, O.I. Micic, A.J. Nozik, A.L. Efros, Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots, Nano Lett. 5 (5) (2005) 865–871. [16] W. Zhu, L. Xu, J. Ma, R. Yang, Y. Chen, Effect of the thermodynamic properties of W/O microemulsions on samarium oxide nanoparticle size, J. Colloid Interface Sci. 340 (1) (2009) 119–125. [17] V.P. Della, I. Kühn, D. Hotza, Rice husk ash as an alternate source for active silica production, Mater. Lett. 57 (4) (2002) 818–821. [18] A.M. Hamza, M.K. Halimah, F.D. Muhammad, K.T. Chan, Physical properties, ligand field and Judd-Ofelt intensity parameters of bio-silicate borotellurite glass system doped with erbium oxide, J. Lumin. 207 (2019) 497–506. [19] I.B. Ugheoke, O. 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Fig. 12. Density and molar volume for samarium oxide nanoparticles doped bio-silica borotellurite glass with different concentration of dopant (lines are drawn as guides to the eyes).

of the prepared glass will decrease and vice versa. The density and molar volume of bio-silica borotellurite doped with samarium oxide nanoparticles are found to be inversely proportional to each other which prove the theoretical relationship as shown in Eq. (9). According to Jearnkulprasert et al., the increment of the molar volume could be related to the role of Sm3+ ions which cause breakage of bridges that contain oxygen ion and produce more nonbridging oxygen in the glass network [50]. The formation of NBOs could be explained in term of the conversion of BO4 to BO3 and TeO4 to TeO3 as proven in the FTIR spectra of the glass system. The increase in the number of NBOs contributes to the growth of free volume and expansion of the glass network, hence increasing the molar volume of the glass. 4. Conclusion The quaternary {[(TeO₂)0.7 (B₂O₃)0.3]0.8 [SiO₂]0.2}1-x {Sm₂O₃ NPs}x glass with different molar fraction of Sm₂O₃ NPs has been fabricated by using the conventional melt-quenching method. The glass composition includes the usage of waste material which is rice husk as the source of amorphous silica making it more economical as compared to the conventional glass system. A high purity of silica is obtained in powder form (ash) after burning process of 2 h. There are various characterization tools used in this research to investigate the structural, optical and physical properties of bio-silica borotellurite glass doped with samarium oxide nanoparticles. XRF spectroscopy proves the high amount of silica which is 98.130% followed by low amount of impurities. The results obtained for FTIR spectra shows four distinct frequency region in the range of 651, 1050, 1225 and 1369 cm−1 that corresponded to TeO3, Si–O–Si bond and BO3 units. HR-TEM analysis proves the presence of samarium oxide nanoparticles in the glass matrix. XRD spectra exhibit a broad hump which reveals the amorphous nature of the prepared glass. The optical absorption spectra were obtained from UV–Vis spectroscopy. The values for optical band gap for indirect and direct transitions have a range of 3.260 to 3.353 eV and 3.356 to 3.405 eV, respectively. Urbach energy shows a trend contrary to the optical band gap. The refractive index, density and molar volume values could be used to determine other parameters such as oxide ion polarizability, electronic polarizability, optical basicity and metallization criterion. Meanwhile, the density and molar volume show an inversely proportional relationship with each other. The density and molar volume exhibit decreasing and increasing pattern, respectively with increasing concentration of samarium oxide nanoparticles. Declaration of Competing Interest Here we declare there is no conflict of interest related to this article. 7

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