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Development of novel optical fibre sensors based on upconverting and gold nanoparticles

Kumar, R. (2020). Development of novel optical fibre sensors based on upconverting and gold nanoparticles. (Unpublished Doctoral thesis, City, University of London)

Abstract

In this work, the Upconverting and Gold nanoparticles were chemically synthesized, coated on the multimode optical fibres and with their performance were evaluated for sensing two keys environmental parameters, temperature and heavy metals present in the aqueous medium, each of which has shown competitive performance with current devices.

In Upconverting Nanoparticles (UCNPs – NaYF4: (18%) Yb3+, (2%) Er3+), thermally coupled green band emission from excited Er3+ ions was used to create optical thermometer, working in the useful range of 295 K – 473 K, with a sensitivity of 4.91 × 10-3 K-1, a temperature resolution of ± 2.7 K and response time of ∼ 5 seconds. The mixture of UCNPs and polydimethylsiloxane shows an excellent linear response (R2 = 0.991) in entire working range of the sensor. The highlights of the developed sensor are its linear response and low temperature synthesis where the required synthesis temperature is around 400 K less than the previously reported Er3+ doped glass-based temperature sensors.

The colloidal solution of Gold Nanoparticles (GNPs) was synthesised, coated on the optical fibre and suitably functionalized with MUA (HS(CH2)10CO2H) to make them selective towards heavy metal ions present in the aqueous solution. The concentration of the heavy metal can be determined from the link between binding rate and the shift of the localized surface plasmon resonance wavelength. The Pb2+ ion sensitivity of the sensor thus created has been determined to be 0.28 nm/mM.

At last, several colloidal solutions of Gold Nano Rods (GNRs) were synthesised, and their quality was determined by developing an algorithm to readily calculate the aspect ratios (ARs) distribution. This is achieved by theoretically fitting the localised longitudinal plasmon resonance of GNRs obtained by UV-visible spectroscopy. The ARs distribution obtained from the use of the algorithm developed have shown good agreement with those theoretically generated one as well as with the previously reported results. The comparison of obtained results with experimentally derived results from the use of expensive transmission electron microscopic images and dynamic light scattering technique shows that the algorithm developed offers a fast and thus potentially cost-effective method to determine the quality of the synthesized GNRs.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > T Technology (General)
Departments: Doctoral Theses
Doctoral Theses > School of Mathematics, Computer Science and Engineering Doctoral Theses
School of Mathematics, Computer Science & Engineering
Date available in CRO: 07 Apr 2021 15:18
Date deposited: 7 April 2021
URI: https://openaccess.city.ac.uk/id/eprint/25881
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