ChemGlobe: Europium: Electronic, thermal, and steric data along with isotopes table.
ChemicalElements.com: Europium: Basic information, atomic structure, and isotopes.
EnvironmentalChemistry.com: Europium: Atomic structure, chemical and physical properties, and table of nuclides.
Europium: Data tables and historic information.
It's Elemental: Europium: Basic physical and historical information.
LANL: Europium: History, production, properties, sources, and uses.
Lenntech: Europium: Physical data, chemical properties, health and environmental effects.
Visual Elements: Europium: Image, source, physical information, and key isotopes.
WebElements: Europium: Extensive information on history, uses, occurrence, compounds, and properties.
Wikipedia: Europium: Properties of the element, including its history, applications, and characteristics.