Synthesis and spectral characterization of Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺ blue-green phosphorous powders by sol-gel method

Highly intense, long persistent Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺ phosphorous powders were prepared for the first time by sol-gel method under argon atmosphere. 2.5 mol% of H₃BO₃ was added as fluxing agent. Characterization of the powders was carried out by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The average particle size of the fabricated phosphor powders was found to be 460 nm in dispersed form in pure water. UV-Vis, steady-state and time resolved fluorescence spectroscopy techniques were used for spectral characterization of the powders. The phosphors exhibited two different emission bands at 449 and 550 nm upon excitation at 400 nm. It is observed that the position and the intensity of the emission band strongly depends on the excitation wavelength and shifts toward lower energy and intensity with increasing wavelength of the excition source. The broad band luminescence characteristics of the Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺ were observed at 492 nm in the absence of the excitation source. The Sr₄Al₁₄O₂₅:Eu²⁺/Dy³⁺ phosphor can be efficiently excited with the visible fraction of the light and show persistent luminescence, long and strong afterglow up to 35 min after removal of the excitation source.