In this study, we have investigated the use of silver cation as nucleating agent in germanotellurite glass matrix of compositions (100-x) [70TeO(2)-10GeO(2)-10Nb(2)O(5)-10K(2)O]-xAg(2)O (x=0-6 mol%), in order to promote bulk crystallization. Density measurements, differential scanning calorimetry, X-ray diffraction, UV-Vis, and Raman spectroscopies have been performed to study the crystallization process. We have observed bulk crystallization of a unique noncentrosymmetric phase, K[Nb1/3Te2/3](2)O-4.8, which has been investigated for its second-order optical activity. Transparent to translucent glass-ceramics have been successfully tailored under thermal treatment and second harmonic generation signals were recorded on the glass-ceramic samples as a function of their synthesis procedure. It is suggested that the second-order optical properties observed are strongly related to the organization of crystallites within phase-separated domains.