Phase evolution in oxy-fluoride glass ceramics

The phase evolution of Er ³⁺ doped oxy-fluoride glass ceramics as a function of temperature has been investigated. Differential thermal analysis showed two successive crystallization exotherms. The first, around 480 °C, was characterized using X-ray diffractometry (XRD) and transmission electron microscopy (TEM) and was related to the formation of a nanocrystalline PbF ₂ phase, hosting most of the rare earth ions. The second crystallization event was studied using XRD, scanning electron microscopy and TEM. It was established that nucleation occurred at the surface, accompanied by Pb loss. Cd-silicate phase together with Zn-fluoride and an Al–Zn oxide phases were present according to energy dispersive X-ray analysis. Not all peaks in XRD traces could be assigned to known compounds. However, several reflections matched well to either CdSiO ₃ (JCPDS [35-810]) or ZnF ₂ (JCPDS [71-1971]).