Phosphoniobate glasses with composition (mol%) (100−x)NaPO3–xNb2O5 (x varying from 11 to 33) were prepared and characterized by means of thermal analysis, Fourier transform infrared spectroscopy, Raman scattering and 31P nuclear magnetic resonance. The addition of Nb2O5 to the polyphosphate base glass leads to depolymerization of the metaphosphate structure. Different colors were observed and assigned as indicating the presence of Nb4+ ions, as confirmed by electron paramagnetic resonance measurements. The color was observed to depend on the glass composition and melting temperature as well. Er3+ containing samples were also prepared. Strong emission in the 1550 nm region was observed. The Er3+ 4I15/2 emission quantum efficiency was observed to be 90% and the quenching concentration was observed to be 1.1 mol% (1.45 × 1020 ions cm−3). Planar waveguides were prepared by Na+–K+–Ag+ ion exchange with Er3+ containing samples. Optical parameters of the waveguides were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique as a function of the ion exchange time and Ag+ concentration. The optimized planar waveguides show a diffusion depth of 5.9 µm and one propagating mode at 1550 nm.

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Compacts of irregular glass particles sinter up to five times faster than sphericalparticle compacts of the same composition. This effect has been attributed to the sharp edges of irregular particles. In this article, we propose and test a phenomenological model for the sintering kinetics of jagged glass particles considering their rounding during sintering. We assume that the small radii of curvature of the particle edges increase as the particles round off and control the sintering rate. We tested the model by measuring the sintering shrinkage of spherical and irregular particle compacts of a diopside (MgO·CaO·2SiO 2 ) glass and using literature sintering data for particles of different shapes of a soda-lime-silica glass. The sintering rate of irregular-particle compacts is initially much higher but tends to reach that of their spherical counterparts as they round off. Our model describes the experimental shrinkage of both glasses and explains the shrinkage anisotropy of irregular-particle compacts in the initial stages of sintering, providing a significant step toward the understanding and description of the sintering kinetics of jagged glass particles.