Eu3+ ion concentration induced 3D luminescence properties of novel red-emitting Ba4La6(SiO4)O:Eu3+ oxyapatite phosphors for versatile applications

A series of Eu3+ ions activated (BaLa6)-La-4(SiO4)(6)O (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 P6(3)/m after annealing at 1400 degrees 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 (D-5(0) -> F-7(2)) along with considerable orange emission (D-5(0) -> F-7(1)) 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.