A blue-emitting SiO2:Eu2+ compound has been successfully synthesized and characterized. The PL intensity of SiO2:Eu0.0022+ compound is about 24 times higher than that of the O-defective SiO2 compound (without activators), which emits blue light. The valence state of the Eu ions responsible for the highly enhanced blue emission was determined to be Eu2+ using reference materials (EuCl2 and EuCl3) and XPS measurements. The Eu2+-activator ions occupied in the interstitial sites of the SiO2 matrix were confirmed by FT-IR, XPS, and 29Si MAS-NMR spectroscopy. Even though the void spaces formed structurally in both α-quartz and α-cristobalite can accommodate Eu2+ ions (ionic radius = 1.25 Å at CN = 8), SiO2:Eu2+ compound fired at 1300°C under a hydrogen atmosphere is destined to be deficient in O or Si atoms, indicating the formation of the wider void spaces in the SiO2 crystal lattice. A sputtered depth profile of SiO2-related compounds obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) corroborates the O-defective SiO2 induced by hydrogen. In particular, the interatomic potentials, depending on the interstitial positions of Eu atoms in α-cristobalite and α-quartz, are calculated based on Lennard-Jones and coulomb potentials. For α-cristobalite, the minimum potential value is -51.47 eV and for α-quartz, the value is 221.8 eV, which reveals that the Eu2+-activator ions more preferably enter the interstitial sites of α-cristobalite than those of α-quartz. Thanks to the stable Eu2+-activator ions enclosed by Si-O linkages, the SiO2:Eu0.0022+ compound emits blue light and its PL emission intensity is about 24 times higher than that of the O-defective SiO2 compound. This phosphor material could be a platform for modeling a new phosphor and for application in the solid-state lighting field.
ASJC Scopus subject areas
- Chemical Engineering(all)