Emission-color change in Eu-doped high-symmetry glaserite-type silicates

Eu3+-doped BaM2MgSi2O8 (M: Ca, Sr, Ba) showed an orange emission under 395-nm excitation light because of D-5(0)-F-4(J) intra-configurational transition in Eu3+ ions. The emission-color turned purple after a few minutes exposure to ultraviolet stimulation light. The observed emission-color change originated in Eu3+ -> Eu2+ photoreduction. As for Ba3MgSi2O8: Eu3+ with low-symmetry P (3) over bar (Z = 3) structure, an intense Eu2+ emission developed by photostimulation. However, the emission intensity gradually decreased under visible light as the reverse reaction Eu2+ -> Eu3+ occurred. In contrast, in BaSr2MgSi2O8: Eu3+ with high-symmetry P (3) over bar m1 (Z = 1) structure, the most intense Eu2+ emission was induced by the photostimulation and maintained even under visible light.