Investigation on crystallization kinetics and luminescent properties of Eu2+/Eu3+-coactivated hexacelsian based glass ceramics

The thermal properties and crystallization behavior of MgO-BaO-SiO2-B2O3-Al2O3 glass have been investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). After crystallization at temperature (800 degrees C) close to the DSC crystallization peak, dendritic hexacelsian crystals are found to form as the major crystalline phase among glass. The crystallization kinetics was studied by analyzing DSC curves with Chen's and Ozawa's equations. The mean crystallization activation energy and Avrami's parameter are evaluated to be 229 kJ/mol and 1.4, indicating that the crystallization process occurs predominantly by surface crystallization as consistent with experimental data. Concurrent emissions of Eu2+ and Eu3+ under 304 nm excitation demonstrate that partial reduction of Eu3+ to Eu2+ occurs, which could be ascribed to the partition of Eu3+ into the precipitated hexacelsian crystals during the sintering process of glass ceramics. These results indicate that glass ceramic route may serve as an intriguing way for synthesis of phosphors applicable to lighting and display fields.