Sol−Gel-Derived BPO₄/Ba²⁺ as a New Efficient and Environmentally-Friendly Bluish-White Luminescent Material

In this paper, BPO 4 and Ba 2+ -doped BPO 4 powder samples were prepared by the sol−gel process using glycerol and poly(ethylene glycol) as additives. The structure and optical properties of the resulting samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), diffuse reflection spectra, photoluminescence (PL) excitation and emission spectra, quantum yield, kinetic decay, and electron paramagnetic resonance (EPR), respectively. It was found that the undoped BPO 4 showed a weak purple blue emission (409 nm, lifetime 6.4 ns) due to the carbon impurities involved in the host lattice. Doping Ba 2+ into BPO 4 resulted in oxygen-related defects as additional emission centers which enhanced the emission intensity greatly (>10×) and shifted the emission to a longer-wavelength region (λ max = 434 nm; chromaticity coordinates: x = 0.174, y = 0.187) with a bluish-white color. The highest emission intensity was obtained when doping 6 mol % Ba 2+ in BPO 4, which has a quantum yield as high as 31%. The luminescent mechanisms of BPO 4 and Ba 2+ -doped BPO 4 were discussed in detail according to the existing models for silica-based materials.