Synthesis and characterization of long persistence Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor prepared by combustion method

Eu²⁺, Dy³⁺ co-doped, strontium aluminate (Sr₄Al₁₄O₂₅) phosphors having high brightness and persistent afterglow were prepared via initial combustion at 600 °C, followed by sintering the resultant combustion ash at different temperatures in a reducing atmosphere of 95% N₂ and 5% H₂. Boron oxide and urea were used as flux and reducing fuel, respectively. The luminescence properties were investigated by changing the amount of flux, fuel to oxidizer ratio (F/O) and final sintering temperature. The crystallization and surface characterization of the precursor and target powder were investigated by X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The photoluminescence (PL) properties were studied by using a PL spectrometer. The results showed that the single-phase Sr₄Al₁₄O₂₅ was formed at 1100 °C and dominated as the temperature was increased to 1500 °C, with a bluish-green emission and a maximum peak at 490 nm, which was attributed to the following typical electronic transition of Eu²⁺: 4f⁶5d¹ → 4f⁷. Co-doped Dy³⁺ ions acted as the trapping center by capturing the free holes in the system, thus generating a persistent afterglow. The emission intensity was influenced by the flux amount and the F/O ratio. Nevertheless, the emission intensity and the afterglow time increased with increasing final sintering temperature up to 1500 °C.