The present article reports the infrared quantum cutting study of the nanophase oxyfluoride vitroceramics Tb(0.7)Yb(5.0)∶FOV. The visible to infrared fluorescence emission spectra, excitation spectra and fluorescence lifetime were measured carefully. The infrared quantum cutting phenomenon {1(［5D4→7F6］(Tb3+), 2(［2F7/2→2F5/2］(Yb3+)} was analyzed based on the above experiments. It was found that the theoretical quantum cutting efficiency is about 121.35% when 5D4 level is excited by 487. 0nm light, and about 136.27% when (5D3, 5G6) levels are excited by 378.0 nm light respectively. Meanwhile, it is first time for the present paper to find a cooperative downconversion phenomenon {2(［(5D3, 5G6)→5D4］(Tb3+), 1(［2F7/2→2F5/2］(Yb3+)}. That is, the authors found for the first time that the donor Tb3+ ion releases two pieces of energy ［(5D3, 5G6)→5D4］ of small energy photon to produce a middle energy photon ［2F5/2→2F7/2］ of acceptor Yb3+ ion.