Photoluminescence and cathodoluminescence properties of Sr2Gd8Si6O26:RE3+(RE3+=Tb3+or Sm3+) phosphors

Trivalent terbium (Tb3+) or samarium (Sm3+) ions individually activated green and orange emitting Sr2Gd8Si6O26 (SGSO) phosphors were synthesized by a citrate sol-gel method. The X-ray diffraction patterns of SGSO:Tb3+ and SGSO:Sm3+ phosphors exhibited the characteristic diffraction peaks of oxyapatite in a hexagonal lattice structure. The photoluminescence (PL) properties at ultraviolet (UV) or near-UV excitation wavelengths were measured for Tb3+ or Sm3+ ions doped SGSO phosphors as a function of its respective concentration. The PL spectra of SGSO:Tb3+ phosphors revealed the characteristic emission peaks of both Gd3+ and Tb3+ ions which are associated with 4f-4f transitions under 274 nm of excitation wavelength. When the concentration of Tb3+ ions increased over 0.05 mol (5 mol%), the emission intensities of 5D3 transitions decreased due to the well-known cross-relaxation process. However, based on the intensities of 5D4 transitions, the optimum concentration of Tb3+ ions was found to be 0.05 mol. Under 404 nm of excitation wavelength, the SGSO:Sm3+ phosphors exhibited the characteristic orange emission at 600 nm due to the 4G5/2→6H7/2 electronic transition. The optimum concentration of SGSO:Sm3+ phosphors was found to be 0.02 mol. The decay curves of the optimized SGSO:Tb3+ and SGSO:Sm3+ phosphors were well fitted to single exponential functions and their lifetimes were calculated. Furthermore, the optimized phosphor samples showed good thermal stability. Likewise, cathodoluminescence properties were also studied for the optimized samples as a function of filament current and accelerating voltage. The Commission International de I-Eclairage chromaticity coordinates were calculated for the SGSO:Tb3+ and SGSO:Sm3+ phosphors.