Structural influence on the photoluminescence properties of Eu3+ doped Gd3MO7 (M = Nb, Sb, and Ta) red phosphors.

New red phosphor materials of general formula Gd3-xMO7:xEu(3+) (M = Nb, Sb, and Ta) were prepared using a high temperature solid state reaction route. Detailed structural studies using XRD, FT-IR and Raman spectroscopic techniques showed that niobate and tantalate samples crystallized in the weberite type structure whereas the antimonate sample in the fluorite structure. Photoluminescence properties of the three compositions are correlated with their crystal structures. It was observed that more ordering occurs in the lattice when an M site is doped from Sb to Nb to Ta. Although niobate and tantalate samples possess similar structures more distortions were noticed in the tantalate sample increasing the radiative transition probabilities. Due to the more ordered structure of the Gd3TaO7 host lattice resulting in a more uniform distribution of Eu(3+) ions, the tantalate system showed better luminescence properties. The variation in the luminescence intensity with various Eu(3+) concentrations in the Gd3TaO7 host lattice was also studied to calculate the optimum doping concentration.