Effects of Composition Variations on the Crystalline Phases and Photoluminescence Properties of Ca2+xMgSi2Eu0.025O7+x Phosphors

A solid-state reaction method was used to synthesize Ca 2+ x MgSi 2 Eu 0.025 O 7+ x ( x = 0–1.0) powders in the air atmosphere and in a reduction atmosphere (95% N 2 + 5% H 2 ) at 1350 °C and 4 h, and the reduction atmosphere was removed at 800 °C. Only the Ca 2 MgSi 2 O 7 phase was found in the XRD pattern of the synthesized Ca 2 MgSi 2 Eu 0.025 O 7 powder. The first important discovery was that when the x value of Ca 2+ x MgSi 2 Eu 0.025 O 7+ x powders was increased from 0.2 to 0.8, both Ca 2 MgSi 2 O 7 and Ca 3 MgSi 2 O 8 phases coexisted in the synthesized Ca 2+ x MgSi 2 Eu 0.025 O 7+ x powders, and the diffraction intensity of the Ca 2 MgSi 2 O 7 (Ca 3 MgSi 2 O 8 ) phase decreased (increased) with the x value. The second important discovery was that the Ca 2 MgSi 2 Eu 0.025 O 7 phosphor exhibited stronger photoluminescence excitation (PLE), photoluminescence (PL), and decay curve properties than the Ca 2.2 MgSi 2 Eu 0.025 O 7.2 phosphor, and the Ca 3 MgSi 2 Eu 0.025 O 8 phosphor exhibited stronger PLE, PL, and decay curve properties than the Ca 2+ x MgSi 2 Eu 0.025 O 7+ x phosphors for x = 0.4, 0.6, and 0.8. For x = 0.2–0.8, the PL spectra of the Ca 2+ x MgSi 2 Eu 0.025 O 7+ x phosphors were a combination of the PL spectra of Ca 2 MgSi 2 Eu 0.025 O 7 and Ca 3 MgSi 2 Eu 0.025 O 8 phosphors. The third important discovery was that as the x value was increased, the maximum emission peak wavelengths of the Ca 2+ x MgSi 2 Eu 0.025 O 7+ x phosphors shifted to a lower value, the maximum emission intensity of the PL spectra increased, and the emission light changed from green and cyan to blue.