Study of micro-structural properties of ion-exchanged and treated glasses by confocal Raman spectroscopy

Ion-exchange technology in silicate glass is becoming an important field for serving as an available platform to study the general properties of waveguiding and integrated optics structures. In fact, glass modification by ion-exchange technique is exploited in the preparation of numerous optical materials, ranging from optical waveguides to non-linear optical nanocomposite materials, which are essential constituents of functional photonic devices for optical communications, sensing and computing. Especially in limited-space devices, like computers and telecommunications switches, these waveguides will have to be fabricated on or within monolithic substrates to save space, increase reliability, improve performances, and, last but least, reduce the cost. These properties of optical waveguides integrated on glass substrates are also crucial for the future development of photonic systems as integrated circuits (ICs) in the large and complex electronic systems. The wave-guiding developments in the field of integrated photonics calls for the need of understanding the structural evolution of host glass matrix and the state modification of incorporated metal species during ion- exchange and during subsequent treatments. Ion-exchange and ion-implantation are the two most exploited techniques for glass doping, both of which emerge with number of limitations and constraints. The main drawbacks of the ion-implantation technique are shallow penetration depth, sputtering of the host substrate, and damage of the local structure. While the ion-exchange process is usually realized by immersing silicate glass slides in a molten salt bath containing the dopant ions, which are driven into the glass by the chemical potential gradient, and replace alkali ions of the glass matrix that are released into the melt bath. In this way, metal ionic species diffuse into the glass network, which is accompanied by the significant micro-structural changes of the ion sites of the glass network. In this thesis, we present Raman micro-spectroscopic investigations into the silver ion-exchange in silicate glasses with the aim to enlighten (i) the effect of silver incorporation into the glass matrix on the glass microstructure and (ii) to extract information on the silver state modification as a function of both the silver concentration on the surface of the glass and its depth beneath the surface. Ion-exchanged samples were produced by immersing silicate glasses in NaNO3:AgNO3 molten salt baths with different molar ratios of silver nitrate, and then underwent to different energy treatments, for instance, thermal annealing in the air at different temperature and laser irradiation with different energy density and wavelengths. They are characterized by various spectroscopic techniques to improve our understanding related to the Ag clustering phenomena, to control Ag nanoparticles size and size distribution and ultimately to tune the optical properties of this nanocomposite system and finally to establish suitable methodologies for the controlled preparation of nanocomposite glass with improved performances. The final party of this thesis deals with the doping of multivalent transition metal ions into the silicate glass which is very important to realize the active integrated optical devices. A range of chromium doped silicate glass were prepared by the thermal diffusion process and Field Assisted Solid State Ion Exchange (FASSIE) process and characterized by micro-Raman spectroscopy. The very promising results obtained by this technique regarding the diffusion of multivalent ions up to few microns have actually opened new ways concerning the understanding of the incorporation mechanism of multivalent dopants and their diffusion response to the experimental conditions.