From Phase Separation to Nanocrystallization in Fluorosilicate Glasses: Structural Design of Highly Luminescent Glass-Ceramics

Tremendous enhancement of optical emission efficiency was achieved in fluorosilicate glasses by growing lanthanide doped fluoride nanocrystals embedded in oxide glass matrix. The formation mechanism of the microstructure was elucidated by combining solid-state NMR, scanning TEM, EDX map, and large-scale molecular dynamics simulations. The results reveal that the growth of fluoride nanocrystals in fluorosilicate glass was originated from fluoride phase separation. Atomic level structures of phase separation of fluoride-rich regions in oxyfluoride glasses matrix were observed from both EDX maps and MD simulations, and it was found that, while silicon exclusively coordinated by oxygen and alkali earth ions and lanthanide mainly coordinated by fluorine, aluminum played the role of linking the two fluoride glass and oxide glass regions by bonding to both oxygen and fluoride ions.