Incommensurately Modulated Crystal Structure and Photoluminescence Properties of Eu2O3- and P2O5-Doped Ca2SiO4 Phosphor

We prepared four types of Eu2O3- and P2O5-doped Ca2SiO4 phosphors with different phase compositions but identical chemical composition, the chemical formula of which was (Ca1.950Eu0.0133+?(0.037))(Si0.940P0.060)O-4 (? denotes vacancies in Ca sites). One of the phosphors was composed exclusively of the incommensurate (IC) phase with superspace group Pnma(0 beta 0)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 beta-Ca2SiO4-related layers with an interlayer. The incommensurate modulation with wavelength of 4.110 x 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 beta-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 Eu3+ ion in the crystal structures of beta- and IC-phases might be closely related to the photoluminescence intensities of the phosphors.