Synthesis and luminescent properties of novel red-emitting CaGd4O7: Eu3+ nanocrystalline phosphors

We reported the novel red-emitting phosphors of trivalent europium (Eu3+) ions activated CaGd4O7 (CG) prepared by a sol-gel method. After the samples were annealed at 1500 degrees C, the X-ray diffraction patterns confirmed their monoclinic structure and the transmission electron microscopy image showed the nano-crystallinity of the CG: Eu3+ phosphor. The photoluminescence excitation spectra exhibited the efficient energy transfer from the Gd3+ to Eu3+ by overlapping the f-f transition of Gd3+ excitation band with charge transfer band of Eu3+ ions. The photoluminescence (PL) spectra showed the emission band in the entire visible region at lower Eu3+ concentration and the red emission at higher Eu3+ concentration. All the decay curves were well fitted by single exponential functions. The temperature dependent luminescence measurements were performed for identifying the thermal stability of CG: Eu3+ phosphors at elevated temperatures. The cathodoluminescent (CL) spectra also presented a similar behavior to that observed in PL spectra. Form the PL, CL, and decay analysis the optimum concentration of Eu3+ ions in the CG host lattice was found to be 5 mol%. The CIE chromaticity coordinates varied from yellow to red in visible spectral region by increasing the Eu3+ concentration. (C) 2012 Elsevier B.V. All rights reserved.