Currently ${\mathrm{Er}}^{3+}$ -doped fluorides are being used as upconversion phosphors to enhance the efficiency of Si solar cells, to our knowledge. However, this enhancement is strongly limited owing to the small solar spectral range around $1540\mathrm{nm}$ that is used. We demonstrate that ${\mathrm{Ho}}^{3+}$ -doped oxyfluoride glass ceramics are adequate to enlarge the Si sub-bandgap region around $1170\mathrm{nm}$ that can be transformed into higher-energy photons, showing an upconversion efficiency 2 orders of magnitude higher than the precursor glass. As these materials are transparent at $1540\mathrm{nm}$ , they can be used complementarily with ${\mathrm{Er}}^{3+}$ -doped phosphors for the same purpose.