Study of controlling phase separation in Yb3+-doped fluorophosphate glasses via molecular dynamics simulations

Yb3+-doped fluorophosphate (FP) glasses are considered to be important laser glass materials with wide appli-cation prospects. However, fluorine phase separation greatly affects the lasing properties of the materials. Be-sides, understanding the phase separation mechanism of FP glass and finding practical methods to control it remain unsolved problems. Herein, we study the phase separation of Yb3+-doped FP glass with the compositions of P2O5-Al2O3-CaF2-YbF3 based on molecular dynamics simulations. The results reveal immiscible behaviors that the glass separates into fluoride-rich phase and aluminophosphate-rich residual matrix. The Al3+ coordi-nated with both O2-and F-form the [Al(O,F)n] polyhedrons on oxide-fluoride interface. Furthermore, to un-derstand the structure of Al3+ dependent glass phase, we generate a series of FP glasses by replacing Ca2+ with Al3+. Those models indicate that [Al(O,F)n] polyhedron plays an important role in breaking the connection of fluoride-rich regions, preventing the further growth of fluoride phase and stabilizing the double-phase structure effectually.