Incommensurately Modulated Crystal Structure and Photoluminescence Properties of Eu(2)O(3)- and P(2)O(5)-Doped Ca(2)SiO(4) Phosphor

We prepared four types of Eu(2)O(3)- and P(2)O(5)-doped Ca(2)SiO(4) phosphors with different phase compositions but identical chemical composition, the chemical formula of which was (Ca(1.950)Eu(3+)(0.013)☐(0.037))(Si(0.940)P(0.060))O(4) (☐ denotes vacancies in Ca sites). One of the phosphors was composed exclusively of the incommensurate (IC) phase with superspace group Pnma(0β0)00s and basic unit-cell dimensions of a = 0.68004(2) nm, b = 0.54481(2) nm, and c = 0.93956(3) nm (Z = 4). The crystal structure was made up of four types of β-Ca(2)SiO(4)-related layers with an interlayer. The incommensurate modulation with wavelength of 4.110 × b was induced by the long-range stacking order of these layers. When increasing the relative amount of the IC-phase with respect to the coexisting β-phase, the red light emission intensity, under excitation at 394 nm, steadily decreased to reach the minimum, at which the specimen was composed exclusively of the IC-phase. The coordination environments of Eu(3+) ion in the crystal structures of β- and IC-phases might be closely related to the photoluminescence intensities of the phosphors.