Effect of Bi3+on crystal structure and optical properties of Gd3PO7: Eu3+ phosphors

This work studies the effect of Bi3+ on crystal structure and emission intensity of Gd3PO7:Eu3+ phosphor. Eu3+ and Bi3+ ions co-doped Gd3PO7 materials have been fabricated via the solid-state reaction at 1050 degrees C. Structural and morphological characteristics of the Gd3PO7:Eu3+ prepared samples were studied by X-ray diffraction and SEM image techniques, which shows the intense diffraction peaks shift to a higher angle due to the difference in ion radii of Bi3+, Eu3+, and Gd3+. The effect of the added Bi3+ ions on the luminescent properties of Gd3PO7: Eu3+,Bi3+ phosphors was investigated via the asymmetry ratio (R) and intensity parameters (Omega lambda) calculated from the emission spectra and Judd-Ofelt theory. The result reveals that the asymmetry at Eu3+ sites in the prepared samples containing Bi3+ ions increases, which is due to the difference in the radii of Bi3+ compared to Gd3+ and Eu3+ ions in the Gd3PO7 host lattice. This increase of the asymmetry at Eu3+ sites enhances the red-emission of the Gd3PO7:Eu3+,Bi3+ phosphors. The luminescence quantum efficiency (eta) of Eu3+ emission, which was calculated from the experimental and calculated lifetimes, reaches a higher value for the samples containing Bi3+ ions. The overall emitted emission of Gd3PO7:Eu3+,Bi3+ phosphors with various Bi3+ concentrations was also characterized by the CIE chromaticity coordinates and the correlated color temperature (CCT). Among the Gd3PO7:Eu3+,Bi3+ prepared samples, the sample with 3.0 mol% Bi3+ reaches a deep red emission with CIE coordination (0.656, 0.338), which is near the standard red light.