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Fabrication of Fiber Optic Based Temperature Sensor
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ScienceDirect Materials Today: Proceedings 9 (2019) 164–174
www.materialstoday.com/proceedings
ICNAN 2016
Fabrication of Fiber Optic Based Temperature Sensor S. Narasimmana, K. Harish Babua, L. Balakrishnanb,*, S.R. Meherb, R. Sivacoumarc and Z.C. Alexc a
School of Electronics Engineering, VIT University, Vellore 632 014, India Department of Physics, Government College of Technology, Coimbatore 641 013, India c Department of Sensor and Biomedical Technology, School of Electronics Engineering, VIT University, Vellore 632 014, India b
Abstract The metal oxide semiconductors (ZnO, SnO2, Al2O3 and TiO2) were synthesized by co-precipitation method. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and UV-Visible spectrometer in diffused reflectance (DR) mode. The XRD results stipulated that the ZnO nanoparticle is crystallized in hexagonal wurtzite structure, SnO2 nanoparticles in rutile tetragonal structure, Al2O3 nanoparticle in rombohedral structure and TiO2 nanoparticle in rutile anatase structure. The SEM investigation affirms that all the synthesized nanopowders are composed of uniformly distributed grains. The UV-Vis spectrum proclaimed that the synthesized nanoparticles having the band gap of 3.2 eV (ZnO), 3.3 eV (SnO2) and 3.5 eV (TiO2) respectively. The synthesized nanoparticles were replaced with small cladding region of the optical fiber and act as a temperature sensing materials. The temperature sensing characteristics of the synthesized nanoparticles were investigated for broad wavelength range (200-1000 nm). It reveals that the synthesized Al2O3 nanoparticles were given linear and high sensitivity (~27) at 697 nm compared with other sensing materials. Further, we have studied the wavelength dependent temperature sensing characteristics of Al2O3nanopowders and it show better sensitivity (~34) in blue wavelength region (450 nm-495 nm). © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanoscience and Nanotechnology (ICNAN’16). Keywords: Metal oxide; nanopowder; fiber optic sensor; temperature sensing. 1. Introduction During recent decades, optical fiber technology was benchmarking one for scaling many physical parameters. Among those physical parameters, temperature is highest significant factor to measure environmental status, widely used in device manufacturing industries and research fields. Nevertheless, there are numerous amount of Corresponding author. Tel.: +91-9944881875. E-mail: [email protected] (L. Balakrishnan).2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanoscience and Nanotechnology (ICNAN’16*).
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temperature sensors existed using different principles. However, the uniqueness that accomplishes fiber optic sensors agreeable over other conventional sensors are anti-electromagnetic interference and more accurate even in harsh environments [1].Metal oxide nanoparticles play a vital role in the sensor field due to their enhanced optical, chemical and electrical properties. Metal oxide nanoparticles have been propounded to be the powerful candidate for biological and gas sensing applications [2].In this work, a study on the characteristics of fiber optic temperature sensor with various metal oxide nanoparticles (ZnO, SnO2, Al2O3 and TiO2) as the sensing material.Commonly, choosing the sensing material is quite complicate process. The sensing material should possess high melting point, good thermal expansion coefficient, chemical stability under temperature variation and also high index of refraction. The sensing mechanism besides the temperature sensor was achieved by thermo optic effect [3]. This article aims the synthesis and characterization of ZnO, SnO2, Al2O3 and TiO2 nanoparticles prepared by coprecipitation technique. The structural, optical and morphological characteristic of the powders has been investigated using X-ray diffraction, UV-Vis spectroscopy and scanning electron microscope. Until now, many reports on temperature sensing involves microfiber knot resonator based on change in resonance wavelength [4], temperature cross sensitivity feature of refractive index sensitive device using water-glycerin solution as sensing medium [5], dielectric multilayer film on sapphire fiber tip based on wavelength shift for high temperature sensing [6] and fiber bragg grating based on wavelength shift [7]. In our report, we have developed a simple method of measuring temperature based on fiber optic clad modification technology from the intensity change due to the change in thermo-optic effect of the sensing material. The modified cladding was accomplished by abolishing a middle fragment of the cladding of the optical fiber and supplanting it with metal oxides. The light intensity propagated through the optical fiber is highly sensitive to the variation in the refractive index of the cladding, which is affected by temperature to be detected. 2. Experimental procedure: 2.1. Materials Zinc acetate, tin (II) chloride, aluminium Chloride and tittaniumisopropoxide (TTIP) were purchased from Sigma Aldrich. Sodium hydroxide and Ammonium hydroxide and Sodium bicarbonate were procured from Merck chemical company. All chemical reagents were of highly purified and were used without further purification. The nanoparticles were synthesized by co-precipitation method. 2.2. Synthesis of ZnO nanoparticles 1.2 g of Zn(CH3COO)2. 2H2O (0.2 M) and 1.8 ml of C6H15NO3 (0.5 M) were added with 50 ml of distilled water and stirred forcefully for 5 h. 50 ml of 2M NaOH stock solution was spilled drop by drop into the mixed solution under constant stirring until it reaches the pH value of 8.0[8]. Further, the reacted solution was kept at room temperature for 24 h. Then, the resultant white precipitate was cleaned with double distilled water to remove impurities and filtered with whatman filter paper (pore size 0.2 μm). Finally, the nanoparticles were calcined at 600 °C for 4 h. 2.3. Synthesis of SnO2 nanoparticles The SnO2 nanoparticles was synthesized by using SnCl4 in place of Zn (CH3COO)2. 2H2O in the above explained experimental procedure. The nanoparticle was precipitated by adding 50 ml of 2 M NH4OH drop wise into the mixed solution until the pH of the solution reaches 8.0[9]. The resultant powder was filtered and calcined at 600 °C for 4 h. 2.4.Synthesis of Al2O3 nanoparticle The Al2O3 nanoparticles were synthesized by using AlCl3 precursor. The nanoparticle was precipitated by adding 50 ml of 1 M Na2CO3 drop wise into the mixed solution till the pH reaches 8.0[10]. The resultant nanoparticles was filtered and calcined at 600 °C for 4 h. 2.5. Synthesis of TiO2 nanoparticles For the synthesis of TiO2nanopaticles, Tittaniumisopropoxide (TTIP, Ti (OCH(CH3)2)4 was used as precursor and NaOH act as precipitating agent. 25 ml of 0.2 M TTIP and 25 ml of C6H15NO3 (0.5 M) were mixed and stirred
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strenuously for 5 hrs. 50 ml of NaOH stocksolution was spilled drop by drop into the mixed solution till the pH value of the solution reaches 8.0[11]. Finally, the resultant nanoparticles were filtered and calcined at 600 °C for 4 h 2.6. Sensor Region Preparation The schematic diagram of the metal oxide coated (ZnO, SnO2, Al2O3 and TiO2) temperature sensing setup is shown in Fig. 1. A broadband light source (SLS201/M) with the wavelength range from 300 to 2600 nm and optical spectrometer (CCS200/M) with the wavelength range of 200 to 1000 nm was used to observe the transmitted light spectra of our propounded sensor. The fiber optic temperature sensing was accomplished by cladding modification method (CMM). In an optical fiber (PMMA), a middle fragment (3 cm length) was denuded and etched using acetone solution. The synthesized metal oxide nanoparticles (ZnO, SnO2, Al2O3 and TiO2) were mixed with double distilled water to make a paste and coated over the etched surface by dip coating method to the thickness of 20 μm. Then, the coated optical fiber was dried at room temperature and used as sensing region. The sensing region was kept in temperature sensing chamber and the temperature level was controlled by microcontroller connected heater. The two ends of the fiber were clipped with the holder which precludes the interference from external disturbances. The sensing chamber was tightly sealed with glue.
Fig. 1.Fiberoptictemperature sensing setup. The optical fiber was heated up from 35 °C to 75 °C with the step interval of 5 °C using microcontroller connected heater. The intensity variation was measured at each interval of 5 °C. The basic principle besides the temperature sensing is mainly due to change in refractive index because of the thermal expansion and thermo-optic effect. The reason for the change in intensity variation for the clad modified fiber upon the temperature change is based on the following relation [12], ∆ ∆
∆
∆
temperature
(1) (2)
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Where, η is initial refractive index of the sensing material, ∆η is the change in refractive index, ∆I is change in intensity, ∆L is change in plastic fiber length, ∆T is change in temperature,ηf is refractive index of the fiber core, α f is the thermal expansion coefficient (TEC) of fiber and α MO is TEC of the metal oxides. dηf/dTis the thermo-optic coefficient (TOC) of fiber and dηMO/dT is TOC of metal oxides. 3. Results and Discussion 3.1. Structural analysis The XRD analysis was taken out to study the crystal structure of synthesized metal oxide nanoparticles (ZnO, SnO2, Al2O3 and TiO2). Fig. 2(a) and (b) shows the XRD pattern of ZnO and SnO2 nanoparticles. It seems that ZnO and SnO2 nanoparticles were crystallized in hexagonal wurtzite structure (JCPDS No. 36-1451) [13] and tetragonal rutile structure (JCPDS No. 88-0287) [14], respectively. Likewise, Fig. 2(c) and (d) shows that TiO2 and Al2O3 nanoparticles were crystallized in rutile anatase structure (JCPDS No. 21-1276) [15] and rombohedral structure (JCPDS No. 42-1468) [16], respectively. No other secondary peaks were revealed within the XRD detection limits. The average crystallite size and strain of the nanoparticles are appraised from Williamson and Hall (W-H) plot. The W-H equation for Cauchy-Lorentzian is given by [17],
4
(3)
Fig. 2.XRD pattern of synthesized nanopowders (a) ZnO (b) SnO2 (c) TiO2 and (d) Al2O3.
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where, D is the crystallite size, C is the shape factor usually taken to be 0.89 (for spherical shape), β is full width at half maximum (FWHM), θ is Bragg’s diffraction angle and λ is the wavelength of radiation (λ=1.54 Å). The equation 1 implies straight line, the value of D and ε have been obtained from the y-axis intercept and slope, respectively of βcosθ vs 4sinθ plot (Fig. 3). From linear fit to the data, the average crystallite size and strain of the nanoparticles are extracted as 52.7 nm and 5.602×10-4 (for ZnO), 31.3 nm and 1.897×10-4 (for SnO2), 48.9 nm and 6.612×10-4 (for TiO2) and 34.2 nm and 5.876×10-4 (for Al2O3), respectively. Further, it has been seen that in Fig. 3 (a), (c) and (d) the deviation of data from the linear fit is found to be minimum compared to Fig. 3 (b), which might be due to the irregularity in grain size distribution.
Fig. 3.W-H plot of synthesized nanopowders (a) ZnO (b) SnO2 (c) TiO2 and (d) Al2O3. Fig. 4.shows the surface morphology of the synthesized metal oxide nanoparticles (ZnO, SnO2, TiO2 and Al2O3) at different magnification.It exhibits the formation of flake (Fig. 4(a)) and spherical (Fig. 4(b) & (c)) shaped nanoparticles with uniform distribution. Fig. 4(d) shows the formation of agglomerates composed of nanograins. Fig. 5.indicates the elemental composition of synthesized metal oxide nanoparticles (ZnO, SnO2, TiO2 and Al2O3). It affirms that Zn and O present in ZnO, Sn and O present in SnO2,Ti and O present in TiO2 and Al and O present in Al2O3 nanoparticles respectively.
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Fig. 4. SEM micrographs of (a) ZnO, (b) SnO2, (c) TiO2, and (d) Al2O3nanopowders.
Fig. 5. EDS spectrum of synthesized (a) ZnO, (b) SnO2, (c) TiO2 and (d) Al2O3nanopowders.
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3.2. Optical analysis
Fig. 6.Absorptionspectraofsynthesizednanopowders.Inset: Tauc's plot. The diffused reflectance spectra of synthesized metal oxide nanoparticles (ZnO, SnO2,TiO2 and Al2O3) were shown in Fig. 6. A strong absorption was obtained at 365 nm (for ZnO), 280 nm (for SnO2) and 345 nm (for TiO2) due to electron excitation from valence band to conduction band. The optical energy bandgap was appraised from Tauc’s relation and is written as [18], (4) where α is coefficient of absorption, C is a constant, Eg is energy band gap, hν is the photon energy and m is an exponent which takes the value depends on electronic transition. m was substituted by the value of 2 for direct transition and ½ for indirect transition. Inset of Fig. 6shows that the bandgap of the synthesized nanoparticles of ZnO, SnO2 and TiO2as 3.42 eV, 3.4 eV and 3.5 eV, respectively.The absorption spectra of Al2O3 showed negligible absorption in the entire spectral range which implies that the band gap of the synthesized Al2O3 nanoparticles lies 200 nm. 3.3. Temperature sensing mechanism In the propounded sensor, the refractive index of the cladding and core was 1.402 and 1.492, respectively. The sensor works in leaky mode condition as the refractive index of original cladding (nclad=1.402) was modified with synthesized nanoparticles (nZnO=2.004, nSnO2=2.006, nTiO2=2.488 and nAl2O3=1.85) is higher than core (ncore=1.492). The output light intensity varies with respect to the refractive index of the modified cladding material. Fig. 7.Shows the light intensity variation of synthesized metal oxide nanoparticles (ZnO, SnO2, TiO2 and Al2O3) under different temperature from 35 °C to 75 °C with the step interval of 5 °C. The spectrum delivers the three characteristics peaks around 697, 774 and 952 nm, respectively.
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Fig. 7.Spectral response of synthesized nanopowders (a) ZnO (b) SnO2 (c) TiO2 and (d) Al2O3 for various temperature (35 °C to 75 °C ) at 697 nm. It represents that the spectrum endures the intensity variation under different temperature condition.The maximum peak intensity variation was achieved around 697 nm with the variation of the temperature compared with other two characteristic peaks. Fig. 8.shows the light intensity variation of synthesized Al2O3 nanoparticles under different temperature from 35 °C to 75 °C with the step interval of 5 °C at various wavelength ranges (Blue, Green, Orange, Red and Yellow). It has been seen that blue and orange wavelength showed considerable intensity change compared to other wavelengths. It depicts that the fabricated fiber optic temperature sensor can also be operating in both blue and orange wavelength ranges. 3.4. Sensitivity analysis The temperature dependent sensitivity at different temperature was calculated using the below formula [19],
%
IT IR TR
(5)
where, IR is the intensity at room temperature and IT is the intensity at different operating temperature. From Fig. 7, it can be seen that the peak at 697 nm showed maximum intensity variation compared with other peaks.
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Fig. 8.Spectral response of Al2O3nanopowders for various temperature (35 °C to 75 °C)at different wavelength ranges (a) blue, (b) green, (c) orange, (d) red and (e) yellow.
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Hence, the sensitivity of the synthesized nanoparticles was calculated at 697 nm. However, it was achieved maximum sensitivity (~27) for Al2O3 compared with other sensing material (Fig. 9(a)). Furthermore, the temperature sensing study was carried out using Al2O3 at different wavelength of 620 nm, 580 nm, 450 nm, 590 nm and 495 nm for red, yellow, blue, orange and green LEDs, respectively. From the Fig. 9(b), it is seen that the Al2O3 nanoparticle utilized sensor meets better sensitivity (~34) in blue wavelength region (450 nm-495 nm).
Fig. 9.Temperature sensitivityof (a) synthesized nanopowders at 697 nm and (b) Al2O3nanopowder at different wavelengths. 4. Conclusion We have propounded and experimentally evidenced a high performance metal oxide nanoparticles utilized fiber optic temperature sensor. It can be seen that the results betrayed a maximum sensitivity of ~27 for Al2O3 nanoparticle compared other sensing material. Further, Al2O3 nanoparticle utilized temperature sensing was carried out at different wavelength ranges. It was given an enhanced sensitivity of ~34 in blue wavelength region (450-495 nm). Hence, it was experimentally confirmed that the Al2O3nanopowder could be an acceptable candidate for the fabrication of high performance temperature sensors. Acknowledgements The authors express their sincere thanks to Department of Science and Technology (DST), New Delhi, India for providing the financial support through FIST (Fund for Improvement of S&T Infrastructure in Higher Education Institution) project [SR/FST/ETI-015/2011]. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
A. Rahman, K. Panchal, S. Kumar, Opt. Fiber Technol. 17 (2011) 315-320. S. Razzaque, S.Z. Hussain, I. Hussain, B. Tan, Polymers 8 (2016) 156. H. Sun, M. Hu, Q. Rong, Y. Du, H. Yang, X. Qiao, Opt. Commun. 323 (2014) 28-31. X. Zeng, Y. Wu, C. Hou, J. Bai, G. Yang, Opt. Commun. 282 (2009) 3817–3819. H. Sun, M. Hu, Q. Rong, Y. Du, H. Yang, X. Qiao, Opt. Commun. 323(2014) 28–31. C. Huang, D. Lee, J. Dai, W. Xie, M. Yang, Sens. Actuators, B. 232 (2015) 99–102. B. Zhang, M. Kahrizi, IEEE Sens. J., 7(4) (2007) 586-591. K. Pradeev Raj, K. Sadayandi, Physica B 487 (2016) 1–7. Z. Nasir, M. Shakir, R. Wahab, M. Shoeb, P. Alam, R. Hasan Khan, M. Mobin, Lutfullaha, Int. J. Biol. Macromolec. 94 (2017) 554–565.
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A.S. Jbara, Z. Othaman, A.A. Ati, M.A. Saeed, Mater. Chem. Phys. 188 (2017) 24-29. S.R. Meher, L. Balakrishnan, Mater. Sci. Semicond. Process. 26 (2014) 251–258. X. Zeng, Y. Wu, C. Hou, J. Bai, G. Yang, Opt. Commun. 282 (2009) 3817-3819. C.W. Zou, J. Wang, W. Xie, J. Colloid Interface Sci. 478 (2016) 22-28. H. Yllah, I. Khan, Z.H. Yamani, A. Quarashi, Ultrason. Sonochem. 34 (2017) 484-490. S. Dai, Y. Wu, T. Sakai, Z. Du, H. Sakai, M. Abe, Nanoscale Res. Lett. 5 (2010) 1829. B. Sathyaseelan, I. Baskaran, K. Sivakumar, Soft Nanoscience. Lett. 3 (2013) 69-74. Y.T. Prabhu, K. Venkateswara Rao, V.S. Sai Kumar, B. Siva Kumari, World J. Nanosci. Engg. 4 (2014) 21-28. A. Dolgomos, T.O. Mason, and K.R. Poeppelmier, J. Solid State Chem. 240 (2016) 43-48. C. Huang, D. Lee, J. Dai, W. Xie, M. Yang, Sens. Actuators, A.232 (2015) 99-102.
ScienceDirect Materials Today: Proceedings 9 (2019) 164–174
www.materialstoday.com/proceedings
ICNAN 2016
Fabrication of Fiber Optic Based Temperature Sensor S. Narasimmana, K. Harish Babua, L. Balakrishnanb,*, S.R. Meherb, R. Sivacoumarc and Z.C. Alexc a
School of Electronics Engineering, VIT University, Vellore 632 014, India Department of Physics, Government College of Technology, Coimbatore 641 013, India c Department of Sensor and Biomedical Technology, School of Electronics Engineering, VIT University, Vellore 632 014, India b
Abstract The metal oxide semiconductors (ZnO, SnO2, Al2O3 and TiO2) were synthesized by co-precipitation method. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and UV-Visible spectrometer in diffused reflectance (DR) mode. The XRD results stipulated that the ZnO nanoparticle is crystallized in hexagonal wurtzite structure, SnO2 nanoparticles in rutile tetragonal structure, Al2O3 nanoparticle in rombohedral structure and TiO2 nanoparticle in rutile anatase structure. The SEM investigation affirms that all the synthesized nanopowders are composed of uniformly distributed grains. The UV-Vis spectrum proclaimed that the synthesized nanoparticles having the band gap of 3.2 eV (ZnO), 3.3 eV (SnO2) and 3.5 eV (TiO2) respectively. The synthesized nanoparticles were replaced with small cladding region of the optical fiber and act as a temperature sensing materials. The temperature sensing characteristics of the synthesized nanoparticles were investigated for broad wavelength range (200-1000 nm). It reveals that the synthesized Al2O3 nanoparticles were given linear and high sensitivity (~27) at 697 nm compared with other sensing materials. Further, we have studied the wavelength dependent temperature sensing characteristics of Al2O3nanopowders and it show better sensitivity (~34) in blue wavelength region (450 nm-495 nm). © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanoscience and Nanotechnology (ICNAN’16). Keywords: Metal oxide; nanopowder; fiber optic sensor; temperature sensing. 1. Introduction During recent decades, optical fiber technology was benchmarking one for scaling many physical parameters. Among those physical parameters, temperature is highest significant factor to measure environmental status, widely used in device manufacturing industries and research fields. Nevertheless, there are numerous amount of Corresponding author. Tel.: +91-9944881875. E-mail: [email protected] (L. Balakrishnan).2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of International Conference on Nanoscience and Nanotechnology (ICNAN’16*).
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temperature sensors existed using different principles. However, the uniqueness that accomplishes fiber optic sensors agreeable over other conventional sensors are anti-electromagnetic interference and more accurate even in harsh environments [1].Metal oxide nanoparticles play a vital role in the sensor field due to their enhanced optical, chemical and electrical properties. Metal oxide nanoparticles have been propounded to be the powerful candidate for biological and gas sensing applications [2].In this work, a study on the characteristics of fiber optic temperature sensor with various metal oxide nanoparticles (ZnO, SnO2, Al2O3 and TiO2) as the sensing material.Commonly, choosing the sensing material is quite complicate process. The sensing material should possess high melting point, good thermal expansion coefficient, chemical stability under temperature variation and also high index of refraction. The sensing mechanism besides the temperature sensor was achieved by thermo optic effect [3]. This article aims the synthesis and characterization of ZnO, SnO2, Al2O3 and TiO2 nanoparticles prepared by coprecipitation technique. The structural, optical and morphological characteristic of the powders has been investigated using X-ray diffraction, UV-Vis spectroscopy and scanning electron microscope. Until now, many reports on temperature sensing involves microfiber knot resonator based on change in resonance wavelength [4], temperature cross sensitivity feature of refractive index sensitive device using water-glycerin solution as sensing medium [5], dielectric multilayer film on sapphire fiber tip based on wavelength shift for high temperature sensing [6] and fiber bragg grating based on wavelength shift [7]. In our report, we have developed a simple method of measuring temperature based on fiber optic clad modification technology from the intensity change due to the change in thermo-optic effect of the sensing material. The modified cladding was accomplished by abolishing a middle fragment of the cladding of the optical fiber and supplanting it with metal oxides. The light intensity propagated through the optical fiber is highly sensitive to the variation in the refractive index of the cladding, which is affected by temperature to be detected. 2. Experimental procedure: 2.1. Materials Zinc acetate, tin (II) chloride, aluminium Chloride and tittaniumisopropoxide (TTIP) were purchased from Sigma Aldrich. Sodium hydroxide and Ammonium hydroxide and Sodium bicarbonate were procured from Merck chemical company. All chemical reagents were of highly purified and were used without further purification. The nanoparticles were synthesized by co-precipitation method. 2.2. Synthesis of ZnO nanoparticles 1.2 g of Zn(CH3COO)2. 2H2O (0.2 M) and 1.8 ml of C6H15NO3 (0.5 M) were added with 50 ml of distilled water and stirred forcefully for 5 h. 50 ml of 2M NaOH stock solution was spilled drop by drop into the mixed solution under constant stirring until it reaches the pH value of 8.0[8]. Further, the reacted solution was kept at room temperature for 24 h. Then, the resultant white precipitate was cleaned with double distilled water to remove impurities and filtered with whatman filter paper (pore size 0.2 μm). Finally, the nanoparticles were calcined at 600 °C for 4 h. 2.3. Synthesis of SnO2 nanoparticles The SnO2 nanoparticles was synthesized by using SnCl4 in place of Zn (CH3COO)2. 2H2O in the above explained experimental procedure. The nanoparticle was precipitated by adding 50 ml of 2 M NH4OH drop wise into the mixed solution until the pH of the solution reaches 8.0[9]. The resultant powder was filtered and calcined at 600 °C for 4 h. 2.4.Synthesis of Al2O3 nanoparticle The Al2O3 nanoparticles were synthesized by using AlCl3 precursor. The nanoparticle was precipitated by adding 50 ml of 1 M Na2CO3 drop wise into the mixed solution till the pH reaches 8.0[10]. The resultant nanoparticles was filtered and calcined at 600 °C for 4 h. 2.5. Synthesis of TiO2 nanoparticles For the synthesis of TiO2nanopaticles, Tittaniumisopropoxide (TTIP, Ti (OCH(CH3)2)4 was used as precursor and NaOH act as precipitating agent. 25 ml of 0.2 M TTIP and 25 ml of C6H15NO3 (0.5 M) were mixed and stirred
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strenuously for 5 hrs. 50 ml of NaOH stocksolution was spilled drop by drop into the mixed solution till the pH value of the solution reaches 8.0[11]. Finally, the resultant nanoparticles were filtered and calcined at 600 °C for 4 h 2.6. Sensor Region Preparation The schematic diagram of the metal oxide coated (ZnO, SnO2, Al2O3 and TiO2) temperature sensing setup is shown in Fig. 1. A broadband light source (SLS201/M) with the wavelength range from 300 to 2600 nm and optical spectrometer (CCS200/M) with the wavelength range of 200 to 1000 nm was used to observe the transmitted light spectra of our propounded sensor. The fiber optic temperature sensing was accomplished by cladding modification method (CMM). In an optical fiber (PMMA), a middle fragment (3 cm length) was denuded and etched using acetone solution. The synthesized metal oxide nanoparticles (ZnO, SnO2, Al2O3 and TiO2) were mixed with double distilled water to make a paste and coated over the etched surface by dip coating method to the thickness of 20 μm. Then, the coated optical fiber was dried at room temperature and used as sensing region. The sensing region was kept in temperature sensing chamber and the temperature level was controlled by microcontroller connected heater. The two ends of the fiber were clipped with the holder which precludes the interference from external disturbances. The sensing chamber was tightly sealed with glue.
Fig. 1.Fiberoptictemperature sensing setup. The optical fiber was heated up from 35 °C to 75 °C with the step interval of 5 °C using microcontroller connected heater. The intensity variation was measured at each interval of 5 °C. The basic principle besides the temperature sensing is mainly due to change in refractive index because of the thermal expansion and thermo-optic effect. The reason for the change in intensity variation for the clad modified fiber upon the temperature change is based on the following relation [12], ∆ ∆
∆
∆
temperature
(1) (2)
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Where, η is initial refractive index of the sensing material, ∆η is the change in refractive index, ∆I is change in intensity, ∆L is change in plastic fiber length, ∆T is change in temperature,ηf is refractive index of the fiber core, α f is the thermal expansion coefficient (TEC) of fiber and α MO is TEC of the metal oxides. dηf/dTis the thermo-optic coefficient (TOC) of fiber and dηMO/dT is TOC of metal oxides. 3. Results and Discussion 3.1. Structural analysis The XRD analysis was taken out to study the crystal structure of synthesized metal oxide nanoparticles (ZnO, SnO2, Al2O3 and TiO2). Fig. 2(a) and (b) shows the XRD pattern of ZnO and SnO2 nanoparticles. It seems that ZnO and SnO2 nanoparticles were crystallized in hexagonal wurtzite structure (JCPDS No. 36-1451) [13] and tetragonal rutile structure (JCPDS No. 88-0287) [14], respectively. Likewise, Fig. 2(c) and (d) shows that TiO2 and Al2O3 nanoparticles were crystallized in rutile anatase structure (JCPDS No. 21-1276) [15] and rombohedral structure (JCPDS No. 42-1468) [16], respectively. No other secondary peaks were revealed within the XRD detection limits. The average crystallite size and strain of the nanoparticles are appraised from Williamson and Hall (W-H) plot. The W-H equation for Cauchy-Lorentzian is given by [17],
4
(3)
Fig. 2.XRD pattern of synthesized nanopowders (a) ZnO (b) SnO2 (c) TiO2 and (d) Al2O3.
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where, D is the crystallite size, C is the shape factor usually taken to be 0.89 (for spherical shape), β is full width at half maximum (FWHM), θ is Bragg’s diffraction angle and λ is the wavelength of radiation (λ=1.54 Å). The equation 1 implies straight line, the value of D and ε have been obtained from the y-axis intercept and slope, respectively of βcosθ vs 4sinθ plot (Fig. 3). From linear fit to the data, the average crystallite size and strain of the nanoparticles are extracted as 52.7 nm and 5.602×10-4 (for ZnO), 31.3 nm and 1.897×10-4 (for SnO2), 48.9 nm and 6.612×10-4 (for TiO2) and 34.2 nm and 5.876×10-4 (for Al2O3), respectively. Further, it has been seen that in Fig. 3 (a), (c) and (d) the deviation of data from the linear fit is found to be minimum compared to Fig. 3 (b), which might be due to the irregularity in grain size distribution.
Fig. 3.W-H plot of synthesized nanopowders (a) ZnO (b) SnO2 (c) TiO2 and (d) Al2O3. Fig. 4.shows the surface morphology of the synthesized metal oxide nanoparticles (ZnO, SnO2, TiO2 and Al2O3) at different magnification.It exhibits the formation of flake (Fig. 4(a)) and spherical (Fig. 4(b) & (c)) shaped nanoparticles with uniform distribution. Fig. 4(d) shows the formation of agglomerates composed of nanograins. Fig. 5.indicates the elemental composition of synthesized metal oxide nanoparticles (ZnO, SnO2, TiO2 and Al2O3). It affirms that Zn and O present in ZnO, Sn and O present in SnO2,Ti and O present in TiO2 and Al and O present in Al2O3 nanoparticles respectively.
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Fig. 4. SEM micrographs of (a) ZnO, (b) SnO2, (c) TiO2, and (d) Al2O3nanopowders.
Fig. 5. EDS spectrum of synthesized (a) ZnO, (b) SnO2, (c) TiO2 and (d) Al2O3nanopowders.
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3.2. Optical analysis
Fig. 6.Absorptionspectraofsynthesizednanopowders.Inset: Tauc's plot. The diffused reflectance spectra of synthesized metal oxide nanoparticles (ZnO, SnO2,TiO2 and Al2O3) were shown in Fig. 6. A strong absorption was obtained at 365 nm (for ZnO), 280 nm (for SnO2) and 345 nm (for TiO2) due to electron excitation from valence band to conduction band. The optical energy bandgap was appraised from Tauc’s relation and is written as [18], (4) where α is coefficient of absorption, C is a constant, Eg is energy band gap, hν is the photon energy and m is an exponent which takes the value depends on electronic transition. m was substituted by the value of 2 for direct transition and ½ for indirect transition. Inset of Fig. 6shows that the bandgap of the synthesized nanoparticles of ZnO, SnO2 and TiO2as 3.42 eV, 3.4 eV and 3.5 eV, respectively.The absorption spectra of Al2O3 showed negligible absorption in the entire spectral range which implies that the band gap of the synthesized Al2O3 nanoparticles lies 200 nm. 3.3. Temperature sensing mechanism In the propounded sensor, the refractive index of the cladding and core was 1.402 and 1.492, respectively. The sensor works in leaky mode condition as the refractive index of original cladding (nclad=1.402) was modified with synthesized nanoparticles (nZnO=2.004, nSnO2=2.006, nTiO2=2.488 and nAl2O3=1.85) is higher than core (ncore=1.492). The output light intensity varies with respect to the refractive index of the modified cladding material. Fig. 7.Shows the light intensity variation of synthesized metal oxide nanoparticles (ZnO, SnO2, TiO2 and Al2O3) under different temperature from 35 °C to 75 °C with the step interval of 5 °C. The spectrum delivers the three characteristics peaks around 697, 774 and 952 nm, respectively.
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Fig. 7.Spectral response of synthesized nanopowders (a) ZnO (b) SnO2 (c) TiO2 and (d) Al2O3 for various temperature (35 °C to 75 °C ) at 697 nm. It represents that the spectrum endures the intensity variation under different temperature condition.The maximum peak intensity variation was achieved around 697 nm with the variation of the temperature compared with other two characteristic peaks. Fig. 8.shows the light intensity variation of synthesized Al2O3 nanoparticles under different temperature from 35 °C to 75 °C with the step interval of 5 °C at various wavelength ranges (Blue, Green, Orange, Red and Yellow). It has been seen that blue and orange wavelength showed considerable intensity change compared to other wavelengths. It depicts that the fabricated fiber optic temperature sensor can also be operating in both blue and orange wavelength ranges. 3.4. Sensitivity analysis The temperature dependent sensitivity at different temperature was calculated using the below formula [19],
%
IT IR TR
(5)
where, IR is the intensity at room temperature and IT is the intensity at different operating temperature. From Fig. 7, it can be seen that the peak at 697 nm showed maximum intensity variation compared with other peaks.
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Fig. 8.Spectral response of Al2O3nanopowders for various temperature (35 °C to 75 °C)at different wavelength ranges (a) blue, (b) green, (c) orange, (d) red and (e) yellow.
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Hence, the sensitivity of the synthesized nanoparticles was calculated at 697 nm. However, it was achieved maximum sensitivity (~27) for Al2O3 compared with other sensing material (Fig. 9(a)). Furthermore, the temperature sensing study was carried out using Al2O3 at different wavelength of 620 nm, 580 nm, 450 nm, 590 nm and 495 nm for red, yellow, blue, orange and green LEDs, respectively. From the Fig. 9(b), it is seen that the Al2O3 nanoparticle utilized sensor meets better sensitivity (~34) in blue wavelength region (450 nm-495 nm).
Fig. 9.Temperature sensitivityof (a) synthesized nanopowders at 697 nm and (b) Al2O3nanopowder at different wavelengths. 4. Conclusion We have propounded and experimentally evidenced a high performance metal oxide nanoparticles utilized fiber optic temperature sensor. It can be seen that the results betrayed a maximum sensitivity of ~27 for Al2O3 nanoparticle compared other sensing material. Further, Al2O3 nanoparticle utilized temperature sensing was carried out at different wavelength ranges. It was given an enhanced sensitivity of ~34 in blue wavelength region (450-495 nm). Hence, it was experimentally confirmed that the Al2O3nanopowder could be an acceptable candidate for the fabrication of high performance temperature sensors. Acknowledgements The authors express their sincere thanks to Department of Science and Technology (DST), New Delhi, India for providing the financial support through FIST (Fund for Improvement of S&T Infrastructure in Higher Education Institution) project [SR/FST/ETI-015/2011]. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
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