Structural and photo-induced properties of Eu2+-doped Ca2ZnSi2O7: A red phosphor for white light generation by blue ray excitation

We demonstrate Eu2+ ion activated sorosilicate Ca2ZnSi2O7 exhibits a broad emission band centered at 600 nm due to Eu2+ 4f65d1→4f7 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 Eu2+-O bonding and ligand field splitting of 5d levels, are responsible for the long wavelength emission from Eu2+ ions. In addition, the formation of a photo-induced transient Eu3+ state from Eu2+ 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 Eu3+ to Eu2+ ions is evaluated to be 11.0 ms at 77 K by a pump-probe technique.