Phase and photoluminescence evolution of (Mg1−xBax)2SiO4: Eu phosphors

Abstract

(Mg1−xBax)1.95SiO4:0.05Eu phosphors were synthesized by high temperature solid-state reaction at 1200 °C. The x-ray diffraction analysis showed the host phase changing as x value increasing could be denoted as γ-Mg2SiO4, β-Mg2SiO4 mixture (x < 0.2) → Ba2SiO4, β-Mg2SiO4, γ-Mg2SiO4 mixture (0.2 ≤ x < 0.3) → Ba2SiO4, Ba3MgSi2O8, β-Mg2SiO4 mixture (0.3 ≤ x < 0.7) → Ba2SiO4 (x ≥ 0.7). For Ba2SiO4 phase powder (Mg1−xBax)2SiO4 , x ≥ 0.7), the replacement of Mg into Ba ions could improve the crystallization, and Mg2+ ions prefer 9-coodinated Ba2+(II) ions more than 10-coodinated Ba2+(I) ions. Furthermore, there is no change in the phase when Eu ions adding. Photoluminescence spectra analysis showed that (Mg1−xBax)1.95SiO4:0.05Eu phosphors exhibited from typical Eu3+ line emission to typical Eu2+broad band emission under UV excitation, and the powder would be used as green phosphor when x ≥ 0.3. The intensity of mixture green phosphor (0.3 ≤ x < 0.7) increases as x value increases. While, the intensity of Ba2SiO4 single phase green phosphor (x ≥ 0.7) decreases as x value increases. The high resolution emission spectra of (Mg1−xBax)1.95SiO4:0.05Eu (x ≥ 0.7) analysis indicates 10-coodinated Eu2+(I) contributes more than 9-coodinated Eu2+(II) for the green emission, and bigger Eu2+(I)/Eu2+(II) ratio when more Mg2+ ions incorporating to Ba2SiO4 phase crystal. The high-resolution x-ray photoelectron spectroscopy (XPS) analysis of Eu4d showed the Eu ion valence is rarely affected by cation substitution. So the better crystalline and higher Eu2+(I)/Eu2+(II) ratio could used to explain the luminescence improvement of Ba2SiO4 phase green phosphor with Mg2+ cation substitution.