Eu3+ ion concentration induced 3D luminescence properties of novel red-emitting Ba4La6(SiO4)O:Eu3+ oxyapatite phosphors for versatile applications
Abstract
A series of Eu3+ ions activated Ba4La6(SiO4)6O (BLSO:Eu3+) phosphors were synthesized by a modified citrate sol–gel process. The structural properties of these phosphors were explored by means of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The XRD patterns confirmed their oxyapatite structure with the space group of P63/m after annealing at 1400 °C. The scanning electron microscope image exhibited the irregular morphology of BLSO:Eu3+ particles and the elemental mapping confirmed that the Eu3+ ions were distributed homogeneously on the La3+ ion sites. Photoluminescence (PL) excitation spectra of BLSO:Eu3+ exhibited the charge transfer band (CTB) and intense f–f transitions of Eu3+ ions in the violet and blue wavelength regions. The CTB intensity decreased and the f–f transition of Eu3+ ions increased with increasing the Eu3+ ion concentration due to the presence of defects in the 4f and 6h sites of the BLSO host lattice. This feature facilitates the strong absorption in the near-ultraviolet (NUV) region, which is useful for high color rendering index NUV based white light-emitting diodes for display and lighting applications. The PL spectra displayed intense red emission (5D0 → 7F2) along with considerable orange emission (5D0 → 7F1) with good asymmetry ratios and chromaticity coordinates, and exhibited better emission performance than that of commercial Y2O3:Eu3+ phosphors. The three-dimensional PL spectra revealed their strong emission characteristics under UV, NUV and visible excitation wavelengths. The cathodoluminescence properties were also similar to the PL results, confirming that the BLSO:Eu3+ phosphors emit stable red emission under different excitation sources as compared to the commercial Y2O3:Eu3+ phosphors.