Análise do ambiente químico local em rede amorfa e cristalina : o efeito de solicitações mecânicas e térmicas

Abstract

Developing new materials to act as host for rare earth ions is still on the upswing. Even though luminescent properties of these ions are significantly influenced by the local environment in which they are inserted, the structural studies of these matrices and its influence on the optical properties, are rarely considered. This thesis aimed to apply models to study the structural of amorphous networks as well as the modifications induced via both heat treatment processes and high-pressure solicitation. This work describes calcium aluminosilicate glasses undoped and Eu-doped in which 1% of total matrix mass was replaced by Eu2O3. For the first time, the average angles distribution and the restoring force of T-O-T linkages were determined for this glassy system. By using in situ Raman spectroscopy, we have found that inter-tetrahedral angles decrease with pressure and the reduction rate for CAS65 was doubled compared to LSCAS and CAS34 samples. Furthermore, the transformation of the pristine glass into glass-ceramic is becoming increasingly common. Such materials may present more suitable morphology, which can increase the luminescence efficiency of the ions inserted therein. These systems are stable against short wavelength irradiation and high temperatures. They have a much higher thermal conductivity than the materials used up to now. We have checked for alternative methods, over the simple heat treatment, to produce glass-ceramics from these pristine glasses. Specifically, we have obtained homogeneously crystallized matrices using a press-type Belt. Physical and chemical properties as density, hardness and Young's modulus were determined. We have found, for instance, an increase in hardness and the luminescent properties in the glass-ceramics host, especially the emission quantum efficiency, which increased from 45 to 60 % after the simultaneous high pressure and temperature process. We have compared the structure of the hosts by using crystal field parameterization, according to the fluorescence line-narrowing model.