Synthesis and characterizations of novel Sr₂Gd₈(SiO₄)₆O₂:Eu³⁺ oxyapatite phosphors for solid-state lighting and display applications

Various concentrations of Eu³⁺ ions activated oxyapatite structured Sr₂Gd₈(SiO₄)₆O₂ (SGSO:Eu³⁺) phosphors were prepared using a citrate sol-gel technique. The structural properties were analyzed by the X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Morphological studies of these phosphors were carried out by the field-emission scanning electron microscopy (FE-SEM). The XRD patterns confirmed the hexagonal crystal form of oxyapatite structure with the space group of P6₃/m after annealed at 1450 °C, which was also authenticated by the FTIR spectra. The FE-SEM image showed a typical rod-like morphology. The luminescent properties of the SGSO:Eu³⁺ phosphors were investigated with the help of photoluminescence (PL) and cathodoluminescence (CL) analyses. The PL excitation (PLE) spectra exhibited a charge transfer band in the higher energy region and intense excitation bands in the lower energy region. The main excitation bands in the ultraviolet (UV), near-UV and visible regions showed higher intensities as well as better full width at half maximum values as compared to the commercial Y₂O₃:Eu³⁺ phosphors. The PL spectra revealed a stronger emission band with a peak at 613 nm due to the forced electric-dipole transition of ⁵D₀ → ⁷F₂ under different excitation wavelengths, but the SGSO:Eu³⁺ phosphors showed greater emission intensity more than 4 times when compared with the Y₂O₃:Eu³⁺ phosphors under 394 nm excitation. The CL spectra also showed luminescence behavior similar to the PL spectra. Due to the better PL and CL properties, the SGSO:Eu³⁺ phosphors are expected to have potential applications in solid-state lighting industry.