Structural and photo-induced properties of Eu~(2+) -doped Ca_2ZnSi_2O_7: A red phosphor for white light generation by blue ray excitation

摘要

We demonstrate Eu~(2+) ion activated sorosilicate Ca_2ZnSi_2O_7 exhibits a broad emission band centered at 600 nm due to Eu~(2+) 4f~65d~1 → 4f~7 transition, which is compatible for a blue light (～ 450 nm) excitation. Orbital symmetry of the emitting state and the tight coordination of 8 oxygen ions in its layered structure, which enhance covalency of Eu~(2+) -O bonding and ligand field splitting of 5d levels, are responsible for the long wavelength emission from Eu~(2+) ions. In addition, the formation of a photo-induced transient Eu~(3+) state from Eu~(2+) was observed by the irradiation of UV light with an energy being slightly larger than the band gap energy of the host. A recovery life time of the Eu~(2+) to Eu~(2+) ions is evaluated to be 11.0 ms at 77 K by a pump-probe technique.