Crystallization and microstructure of Eu3+-doped lithium aluminophosphate glass

A transparent Eu3+-doped lithium aluminophosphate glass was prepared by melt-quenching technique. The thermal behavior of the glass was investigated by differential thermal analysis (DTA), the structure was studied by X-ray diffraction (XRD) and the morphology was observed by optical polarization microscopy and scanning electron microscopy (SEM). The activation energy of glass transition and the activation energy of crystallization and Avrami exponent have been evaluated under non-isothermal conditions from the data obtained by DTA at different heating rates. DTA curves exhibited an endothermic peak associated with the glass transition and two exothermic peaks. The mean value calculated for the activation energy of glass transition was 545 kJ mol−1. The activation energy of crystallization was ~400 kJ mol−1 for the first exothermic peak and ~170 kJ mol−1 for the second peak. The Avrami exponent was ~1 for both peaks indicating surface crystallization. XRD results showed that the main crystalline phase, aluminum metaphosphate, Al(PO3)3, and aluminum phosphate, AlPO4, were formed together with lithiumbariumphosphate, Li3Ba(PO3)7, during the first exothermic peak and together with bariumpyrophosphate, Ba2P2O7, during the second peak.Morphological study of heat-treated glass samples revealed microstructural features that confirmed a surface crystallization process.