Enhancement of red emission intensity of Ca₂Al₂SiO₇:Eu³⁺ phosphor by MoO₃ doping or excess SiO₂ addition for application to white LEDs

Ca_1.86Al₂(Si_1-xMo_x)O₇:0.14Eu³⁺ and Ca_1.86Al₂Si_1+yO_7+2y:0.14 Eu³⁺ were synthesized by solid-state reaction. X-ray powder diffraction, excitation and emission spectra were used to investigate their structures and photoluminescence properties. The results shows that the phosphor Ca_1.86Al₂SiO₇:0.14Eu³⁺ cannot be excited efficiently by light of 393 nm. The introduced Mo ion does not change the position of the excitation peak, but increases both the absorption at 400nm and the emission intensity of Eu³⁺. The intense red emitting phosphor Ca_1.86Al₂(Si_0.95Mo_0.05)O₇:0.14Eu³⁺ was obtained, which has 67% enhanced luminous intensity compared to that of the undoped sample Ca_1.86Al₂SiO₇:0.14Eu³⁺. Otherwise, SiO₂ excess of non-stoichiometric phosphors Ca_1.86Al₂Si_1+yO_7+2y:0.14Eu³⁺ showed the characteristic pattern of a tetragonal structure with a small SiO₂ concentration. The optimal phosphor of Ca_1.86Al₂Si_1.1O_7.2:0.14Eu³⁺ has a luminous intensity about two times higher than that of the original stoichiometric phosphor Ca_1.86Al₂SiO₇:0.14Eu³⁺. We confirmed that the photoluminescence intensity of the obtained phosphors is fairly enhanced by excessive SiO₂. The mechanism of this photoluminescence enhancement is discussed in this paper. (paper)