Effects of the rare earth modifier on the Brillouin scattering from soda magnesia alumina silicate glasses

Brillouin scattering spectra of rare earth doped glasses have been measured to investigate the differences of optical properties of soda magnesia alumina silicate glasses with different Eu³⁺ and Pr³⁺ concentrations. Measurements of Brillouin frequency shifts and intensities along with refractive indexes and densities allow us to calculate the acoustic sound velocities, elastic and photoelastic constants. The physical significance of the changes in elastic and photoelastic constants as a function of rare earth content and type is discussed. The results on elastic constants show that the glasses become harder with increasing concentration of the high coordinated rare earth modifiers. From Carleton's model, the Lorentz-Lorenz effect dominates P₁₂, while the atomic effect dominates P₄₄ in our glasses. The increase in both the bond polarisability parameter and Poisson's ratio with the rare earth concentration indicates the enhancement in polarisability and ionicity of these glasses.