Preparation and luminescence properties of spherical Sr₄Al₁₄O₂₅: Eu²⁺ phosphor particles by a liquid synthesis

A spherical Sr₄Al₁₄O₂₅:Eu²⁺ phosphor for use in white-light-emitting diodes was synthesized using a liquid-state reaction with two precipitation stages. For the formation of phosphor from a precursor, the calcination temperature was 1,100^°C. The particle morphology of the phosphor was changed by controlling the processing conditions. The synthesized phosphor particles were spherical with a narrow size-distribution and had mono-dispersity. Upon excitation at 395 nm, the phosphor exhibited an emission band centered at 497 nm, corresponding to the 4f⁶5d→4f⁷ electronic transitions of Eu²⁺. The critical quenching-concentration of Eu²⁺ in the synthesized Sr₄Al₁₄O₂₅:Eu²⁺ phosphor was 5 mol%. A phosphorconverted LED was fabricated by the combination of the optimized spherical phosphor and a near-UV 390 nm LED chip. When this pc-LED was operated under various forward-bias currents at room temperature, the pc-LED exhibited a bright blue-green emission band, and high color-stability against changes in input power. Accordingly, the prepared spherical phosphor appears to be an excellent candidate for white LED applications.