Synthesis and luminescent properties of novel red-emitting CaGd ₄O₇: Eu³⁺ nanocrystalline phosphors

We reported the novel red-emitting phosphors of trivalent europium (Eu ³⁺) ions activated CaGd₄O₇ (CG) prepared by a sol-gel method. After the samples were annealed at 1500 °C, the X-ray diffraction patterns confirmed their monoclinic structure and the transmission electron microscopy image showed the nanocrystallinity of the CG: Eu ³⁺ 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.