A theoretical scheme for laser cooling in Tm3+-doped oxy-fluoride glass ceramic (GC) is presented. It is shown that the
unique combination of high chemical and mechanical stability of the oxide glass and low phonon energy of the fluoride
nano-crystals, which trap a majority of Tm3+ ions, is beneficial for laser cooling of solids. The effective embedding of
rare-earth ions in the crystalline phase with low phonon energy provides high quantum efficiency for the 3F4 → 3H6
transition involved in the cooling cycle in the Tm3+ ions, which is a key parameter for laser cooling of solids.