We report the fabrication and spectroscopic characterization of Yb3+-doped phosphate glass, also containing silver nitrate. Scanning electron microscopy (SEM) provides the evidence of the formation of silver nano-particles (SNPs), which are formed as a consequence of melting and thermal decomposition of AgNO3. Absorption spectra of the samples in the visible-to-near-infrared spectral range reveal the presence of bands centered at 410 nm associated with the SNP-plasmon resonance, and at 976 nm due to the Yb3+. Under 916-nm laser-diode pumping, the effect of the SNP reflects that: i) the fluorescence in the 950-nm–1150-nm spectral range is strongly enhanced(~ 30 times), while the fluorescence decay time associated with the 2F5/2 → 2F7/2 transition of Yb3+ increases 25%, and ii) the basic lasing properties (saturation pumping intensity, the emission and absorption cross sections) are substantially improved.