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Title: Linear and Non-Linear Optical Properties of Nanoparticles Dispersed Novel Glasses
Authors: Shivani
Supervisor: Pandey, O. P.
Sharma, Gopi
Keywords: Glass;Gold;Nanoparticles;Z-scan;Nonlinear;Linear
Issue Date: 20-Aug-2020
Abstract: Constant efforts are being made by the researchers to develop a suitable and efficient material to be used for optical applications. Composite materials formed by the incorporation of metal nanoparticles in glass are the most preferred as they exhibit striking third order nonlinearity and ultrafast time response. Moreover, remarkable modification in optical behavior can be achieved by controlling amount, size and shape of the nanoparticles. In addition to this, the local environment around the nanoparticles plays a crucial role which is an intrinsic function of glass composition. In most of the traditional methods, used for the production of such nanocomposites, metallic salts are first introduced in the glass matrix and get transformed to nanoparticles as a result of pulsed laser beam exposure or heat treatment. This post treatment eventually induces crystallization of glass with associated scattering of light and hence, resulting in reduced optical quality of material. In the present work, direct incorporation of metallic nanoparticles in the glass matrix has been studied in detail which could be an effective solution for above-mentioned limitations. The entire work is organized in following eight chapters: Chapter 1 gives a brief description and background of basic phenomena leading to the origin of ultrafast nonlinear response in glass nanocomposites (GNCs). Various fabrication routs followed to prepare such GNCs are discussed along with their real-time limitation to summarize the importance and need of direct incorporation of metallic nanoparticles. Moreover, the basic structure of borate glasses along with their features leading to enhanced nonlinear behavior is discussed in detail. Further, the motive behind using the gold nanoparticles (AuNPs) as filler in the GNCs is given in detail. In the last, importance of rare earth to stabilize metal nanoparticles (AuNPs) with enhanced optical efficiency is discussed. Chapter 2 summarizes the available literature concerning to nonlinear optical behavior of glass and glass nanocomposites. Influence of fabrication route, type of metal nanoparticle and the glass composition on optical behavior is compared for different glass systems. Enhanced luminescence in vicinity of rare earth is also presented here. Large value of figure of merit, fast response time and high nonlinear susceptibility of glasses makes them promising candidates for opto-electronic devices. Based on literature, the last section of this chapter reviews the gaps in study so far along with the proposed objectives of the thesis. Chapter 3 describes the details of experimental procedure followed to achieve the proposed objectives. The detailed methodology adopted for the preparation of AuNPs dispersed GNCs via direct incorporation of as prepared nanoparticles is given in this chapter. Also, adopted characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM), High resolution transmission electron microscopy (HRTEM), Differential thermal analysis (DTA), Density measurements, UV-Vis spectroscopy and Z-scan for structural, morphological, thermal and optical properties, respectively have been discussed briefly. Chapter 4 deals with the optimization of fabrication methods to achieve a homogeneous distribution of AuNPs in the glass matrix through direct incorporation. For this purpose, AuNPs dispersed glasses are prepared via three different methods; (i) drop casting method, (ii) sandwich method and (iii) melt quenching at room temperature. XRD confirms the amorphous nature of glass even after the addition of AuNPs whereas basic structure of glass is composed of BO3 and BO4 units as illustrated from FTIR. FESEM micrographs reveals that the morphology of AuNPs inside the glass is highly dependent on the method of their incorporation. It is also depicted that melt quenching at room temperature method results in uniform distribution of AuNPs and hence used for further sample preparation. Uniform dispersion of AuNPs in glass matrix resulted a high refractive index and large nonlinear optical properties which makes them interesting for plasmonic devices. Chapter 5 focuses on the effect of size and amount of AuNPs along with glass composition on various properties. This chapter is divided into three subsections; (i) the effect of amount of AuNPs, (ii) effect of size of AuNPs, and (iii) effect of variation of Bi-content in the glass. Glasses remains amorphous with variation in any of the above mentioned parameter. FTIR confirms the formation of non-bridging oxygens with the inclusion of AuNPs and increase in bismuth content inside the glass. FESEM results revealed the loss of AuNPs due to evaporation and coagulation. Shielding effect of bonds by nanoparticles results in modification in thermal parameters as observed from DTA results. Increase in bismuth content reduces the glass transition temperature that results in enhanced coagulation. Nonlinear behavior increases with increase in amount of gold and bismuth in the glass whereas it saturates for 40 nm as average particle size. Chapter 6 provides an effective solution to reduce the loss of nanoparticles via evaporation and oxidation occurring during melting because of the high temperature step involved in theirpreparation. The use of refectory material (SiO2) helps in preventing the loss of AuNPs. Here, the higher concentration of AuNPs as a result of the protection from oxidation at high temperature is evidenced from the observed FESEM micrographs along with compromised agglomeration of AuNPs in order to reduce the surface stresses (Ostwald ripening). Moreover, the reduction in glass transition temperature also supported the coagulation of AuNPs. Prepared SiO2 contained GNC samples possess sufficiently high nonlinear refractive index and low absorption as observed from Z-scan. Chapter 7 presents the comparison of stabilizing action of Eu2O3, EuF3 and KSCN on AuNPs. The systematic investigation of glasses containing these stabilizing agents for the optical, structural, thermal and nonlinear optical properties of the synthesized samples has been done. Eu2O3 acting as capping agent on AuNPs seems to be the best stabilizing substance among these three as a result of reduced coagulation of AuNPs as observed in FESEM and HRTEM micrographs. Addition of EuF3 and KSCN could not prevent sufficient coagulation and thermal loss of AuNPs, respectively. The nonlinear refractive index is found to be very high for the prepared glass system. Chapter 8 describes the conclusion drawn from above studies and scope for future work. It gives the comparative structural and thermal characteristics of AuNPs dispersed borate glass samples. The influence of fabrication conditions, AuNPs (amount and size), matrix composition and stabilizing agent on the optical efficiency is compared. Based on the observed results, mono-dispersed (~40 nm) AuNPs in amorphous matrix with high thermal stability and better nonlinear response enables the borate glasses a suitable candidate for fiber drawing, optical switching and optical limiting applications. At the end, possible future scope to enrich the study is presented.
Appears in Collections:Doctoral Theses@SPMS

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