Crystal structure and magnetic-dipole emissions of Sr2CaWO6: RE3+ (RE=Dy, Sm and Eu) phosphors

Highlights: • The as-prepared Sr₂CaWO₆ sample crystallizes in the monoclinic structure. • The PL emission of Sr₂CaWO₆: RE³⁺ is dominated by MD transitions of RE³⁺. • The doped RE3+ ions occupy the centrosymmetric sites of Sr₂CaWO₆ host. • The CIE coordinate of Sr₂CaWO₆: Sm³⁺ is (0.36, 0.30). The Sr₂CaWO₆: RE³⁺ (RE = Dy, Sm and Eu) phosphors with the unusual emissions corresponding to the magnetic-dipole (MD) transition were synthesized via a sol-gel process. The crystal structure, electronic properties, photoluminescence excitation and emission spectra, and fluorescence lifetimes of the as-prepared samples were investigated. X-ray diffraction analysis confirmed that Sr₂CaWO₆ crystallized in the monoclinic structure with the centrosymmetric monoclinic space group (P2₁/n). The indirect band gap for Sr₂CaWO₆ was 4.24 eV, which was calculated within the framework of density functional theory (DFT). The phosphors could be excited by the ultra-violet (UV) light at 280 nm, and exhibited characteristic emissions corresponding to the MD transitions for different RE³⁺ ions. The WO₆ groups in the host lattice can absorb UV light efficiently, and then transferred the energy to activator ions. The results indicated that the doped rare earth ions occupied the centrosymmetric site in Sr₂CaWO₆ lattice. With increasing the concentration of the dopants, the local symmetry of the activator ions can be effectively changed, which resulted in the enhancement of the characteristic emissions dominated by the electric-dipole (ED) transitions of the doped RE³⁺. The Sr₂CaWO₆: Sm³⁺ phosphor exhibited near white emission under radiation of 280 nm.