Sunitha, Sabastin; Dr. M. Kailasnath(Cochin University of Science and Technology, June 12, 2015)
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Abstract:
Polymer Optical Fibers have occupied historically a place for large core flexible fibers operating in short distances. In addition to their practical passive application in short-haul communication they constitute a potential research field as active devices with organic dopants. Organic dyes are preferred as dopants over organic semiconductors due to their higher optical cross section. Thus organic dyes as gain media in a polymer fiber is used to develop efficient and narrow laser sources with a tunability throughout the visible region or optical amplifier with high gain. Dyes incorporated in fiber form has added advantage over other solid state forms such as films since the pump power required to excite the molecules in the core of the fiber is less thereby utilising the pump power effectively. In 1987, Muto et.al investigated a dye doped step index polymer fiber laser. Afterwards, numerous researches have been carried out in this area demonstrating laser emission from step index, graded index and hollow optical fibers incorporating various dyes. Among various dyes, Rhodamine6G is the most widely and commonly used laser dye for the last four decades. Rhodamine6G has many desirable optical properties which make it preferable over other organic dyes such as Coumarin, Nile Blue, Curcumin etc. The research focus on the implementation of efficient fiber lasers and amplifiers for short fiber distances. Developing efficient plastic lasers with electrical pumping can be a new proposal in this field which demands lowest possible threshold pump energy of the gain medium in the cavity as an important parameter. One way of improving the efficiency of the lasers, through low threshold pump energy, is by modifying the gain of the amplifiers in the resonator/cavity. Success in the field of Radiative Decay Engineering can pave way to this problem. Laser gain media consisting of dye-nanoparticle composites can improve the efficiency by lowering the lasing threshold and enhancing the photostability. The electric field confined near the surface of metal nanoparticles due to Localized Surface Plasmon Resonance can be very effective for the excitation of active centers to impart high optical gain for lasing. Since the Surface Plasmon Resonance of nanoparticles of gold and silver lies in the visible range, it can affect the spectral emission characteristics of organic dyes such as Rhodamine6G through plasmon field generated by the particles. The change in emission of the dye placed near metal nanoparticles depend on plasmon field strength which in turn depends on the type of metal, size of nanoparticle, surface modification of the particle and the wavelength of incident light. Progress in fabrication of different types of nanostructures lead to the advent of nanospheres, nanoalloys, core-shell and nanowires to name a few. The thesis deals with the fabrication and characterisation of polymer optical fibers with various metallic and bimetallic nanostructures incorporated in the gain media for efficient fiber lasers with low threshold and improved photostability.
Biju, Francis; Dr. M. L. P. Reddy(Cochin University of Science and Technology, January 6, 2016)
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Abstract:
The fascinating photoluminescence properties of trivalent europium (Eu3+)
coordination compounds have aroused tremendous interest in recent years due
to their potential applications ranging from biomedical analysis to material
science. The Eu3+ ions have excellent luminescent features such as long-lived
excited-state lifetimes (μs–ms range) and narrow, easily recognizable line-like
red emission bands with large Stokes shifts. A big challenge in the chemistry of
lanthanide ions is to develop luminescent europium complexes that can be
sensitized by visible-light. This field has become much more important because
of the demand for less-harmful labelling reagents in the life sciences and lowvoltage-
driven pure-red emitters in optoelectronic. Thus, the primary objective
of the present research work is to design and develop novel visible-light
sensitized Eu3+-β-diketonate complexes with impressive photophysical
propertiesThe thesis comprises of four chapters which are presented as independent
units and therefore the structure formulae, schemes, figures and references are
numbered chapterwise. The introductory chapter highlights a background
sketch of the use of β-diketonates as antenna ligands for Eu3+ ion, the recent
developments in visible light excitable Eu3+-β-complexes and an overview of
the various methods of synthesis of Eu3+-based silica hybrid materials, their
photophysical properties and possible applications