This paper reports on the preparation of novel sol-gel erbium-doped SiO2-based nanocomposites embedded with Nb2O5 nanocrystals fabricated using a bottom-up method and describes their structural, morphological, and luminescence characterization. To prepare the glass ceramics, we synthesized xerogels containing Si/Nb molar ratios of 90:10 up to 50:50 at room temperature, followed by annealing at 900, 1000, or 1100 °C for 10 h. We identified crystallization accompanying host densification in all the nanocomposites with orthorhombic (T-phase) or monoclinic (M-phase) Nb2O5 nanocrystals dispersed in the amorphous SiO2 phase, depending on the niobium content and annealing temperature. A high-intensity broadband emission in the near-infrared region assigned to the 4I13/2 → 4I15/2 transition of the Er3+ ions was registered for all the nanocomposites. The shape and the bandwidth changed with the Nb2O5 crystalline phase, with values achieving up to 81 nm. Er3+ ions were located mainly in Nb2O5-rich regions, and the complex structure of the different Nb2O5 polymorphs accounted for the broadening in the emission spectra. The materials containing the T-phase, displayed higher luminescence intensity, longer 4I13/2 lifetime and broader bandwidth. In conclusion, these nanostructured materials are potential candidates for photonic applications like optical amplifiers and WDM devices operating in the S, C, and L telecommunication bands. Display omitted •Rare earth doped Nb2O5 nanocrystals prepared from a bottom-up approach.•Unusual broadband NIR emission in glass ceramic system.•Structural features tuning the luminescence properties.•Potential as optical amplifiers and WDM devices.•Photonic devices operating in the S, C, and L telecommunication.