Recently, several oxide-based phosphors with excellent luminescence properties have been reported. Especially, the deep-red emitting Ca_1.2Eu_0.8SiO₄ has been prepared by the basis on crystal-site engineering, which shows an emission peak at 653 nm under excitation at 450 nm [1]. The emission wavelength of Ca_1.2Eu_0.8SiO₄ is quite similar to those of commercial red-emitting CaAlSiN₃:Eu²⁺ and Sr₂Si₅N₈:Eu²⁺. The crystal structure of Ca_2-xEu_xSiO₄ is analogous to those of Sr_2-xEu_xSiO₄ and Ba_2-xEu_xSiO₄. Therefore, it is expected that the addition of large amounts of Eu²⁺ ions to Sr_2-xEu_xSiO₄ and Ba_2-xEu_xSiO₄ can also lead to large redshifts in their emission and excitation spectra. In this study, we prepared and characterized Sr_2-xEu_xSiO₄ and Ba_2-xEu_xSiO₄ with a high concentration of Eu²⁺ ions. In the case of Sr_2-xEu_xSiO₄, the emission peak was shifted from 585 nm for Sr_1.9Eu_0.1SiO₄ to 611 nm for Sr_1.2Eu_0.8SiO₄. On the other hand, in the case of Ba_2-xEu_xSiO₄, the emission peak was shifted from 513 nm for Ba_1.9Eu_0.1SiO₄ to 545 nm for Ba_1.2Eu_0.8SiO₄. The right-hand edges of the excitation spectra for both the samples were significantly shifted, by 40-55 nm, to longer wavelengths, allowing for excitation by blue light. The induction of large redshifts in the emission and excitation spectra of both samples could be attributed to the occupancy of Eu²⁺ ions in the polyhedra of Sr(2) or Ba(2) sites, which are smaller and more distorted than the Sr(1) or Ba(1) sites. These results indicate that Sr_1.2Eu_0.8SiO₄ and Ba_1.2Eu_0.8SiO₄ are suitable as red- and green-emitting phosphors for next-generation white-LED applications.

[1] Y. Sato and M. Kakihana et al., Angew. Chem. Int. Ed. 53 (2014) 7756.