Silicate glasses are among the best hosts for rare-earth ions, especially for the development of integrated optic amplifiers and lasers, due to their chemical robustness and adaptability to different waveguide fabrication process. Their application to the manufacturing of optical amplifiers, however, may be limited by the relatively narrow fluorescence bandwidth. Here the results of an in-depth study of the effect of an increasing content of alumina on the broadening of the emission bandwidth are reported. We synthesized and characterized a new set of glasses: their basic composition was of the type SiO2 - Na2O - CaO - Al2O3, with small percentages of P2O5 and K2O. Alumina content was varied from about 1% to 20 mol%. An almost constant concentration of erbium oxide ( ~ 0.4 mol% ) was also present. The spectroscopic properties of these glasses, namely absorption and emission spectra, radiative and experimental lifetimes, are discussed. The characterization of the optical waveguides, fabricated in these glasses by ion-exchange method, is presented as well.