The efficiency of semiconductor solar cells could be greatly increased by down-conversion processes, which efficiently split incident solar photons into couples of photons with energy over the bandgap. Here, we show new down-conversion mechanisms in Er3+-Yb3+ co-doped glass-ceramics, where the ions are hosted by fluoride nanoparticles embedded in silica glass. By this means, 350-550 nm photons, absorbed by Er3+ ions, generate pairs of photons at the range of 650-1550 nm, emitted by Er3+ and Yb3+, with a quantum efficiency approaching the maximum of 200%. (C) 2010 Elsevier B.V. All rights reserved.