Abstract
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 (Ca1.950Eu3+0.013☐0.037)(Si0.940P0.060)O4 (☐ 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-Ca2SiO4-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 Eu3+ ion in the crystal structures of β- and IC-phases might be closely related to the photoluminescence intensities of the phosphors.
Highlights
Rare-earth doped dicalcium silicate (Ca2 SiO4, C2 S) polymorphs have been the subject of extensive study because of the promising applicability of stabilized high-temperature modifications to the phosphor materials of white light-emitting LEDs [1,2,3,4,5,6,7,8]
The incommensurately modulated crystal structure was determined from the X-ray powder diffraction data using a (3 + 1)-dimensional description based on the superspace group Pnma(0β0)00s
We demonstrated a close relationship between the phase composition and PL intensity
Summary
Rare-earth doped dicalcium silicate (Ca2 SiO4 , C2 S) polymorphs have been the subject of extensive study because of the promising applicability of stabilized high-temperature modifications to the phosphor materials of white light-emitting LEDs [1,2,3,4,5,6,7,8]. Eu3+ -activated phosphors, due to the transition of the 5 D0 –7 F2 for Eu3+ ion [3,4]. The photoluminescence (PL) originates from the 4f–4f dipole transitions and, the emission wavelengths are nearly the same among the various types of phosphors with different host materials. The PL intensity has been tunable for Eu3+ -activated lithium tantalite-based phosphors by controlling the coordination environments of the Eu3+ ion [9,10]. We speculated that the PL intensities could be tunable for the Eu3+ -activated C2 S phosphors, depending on the polymorphs stabilized at ambient temperature.
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