Luminescent properties of Gd³⁺ sensitized low-phonon energy CaGd₄O₇:Tb³⁺ green emitting novel phosphors

The trivalent terbium (Tb³⁺) ions activated CaGd ₄O₇ (CG) phosphors were synthesized by a sol-gel method. The characterizations were performed after the samples annealed at 1500 °C. The structural and morphological properties were analyzed from the X-ray diffraction patterns and scanning electron microscope images. The photoluminescence excitation spectra showed a broad-band between the wavelengths 250 and 300 nm, which were overlapped with the Gd³⁺ excitation bands. The photoluminescence spectra exhibited efficient green emission due to the sensitization effect of Gd³⁺ ions on the Tb³⁺ ions when exciting with the Gd³⁺ wavelength at 278 nm. In order to analyze the influence of Tb³⁺ concentration on the luminescence behavior of Tb³⁺ ions in the CG host lattice, the decay curves were measured. The temperature-dependent luminescence measurements were done to identify the thermal stability of CG:Tb³⁺ phosphors at elevated temperatures. The cathodoluminescent spectra also showed a similar behavior to that observed in PL spectra. The CIE chromaticity coordinates as a function of Tb³⁺ concentration were calculated and all the obtained chromaticity coordinates have been placed in the green spectral region.