Synthesis and characterization of Sm3+ activated La1-xGdxPO4 phosphors for white LEDs applications

A series of orange-red light emitting Sm3+ activated La1-xGdxPO4 (0.00 x 1.00) phosphors were synthesized by the solid-state method. The structural parameters were confirmed by the Rietveld refinement method based on powder X-Ray diffraction (XRD) analysis. All the compounds crystallized in the monazite monoclinic structure with space group P 1 2(1)/n 1 (no. 14). The photoluminescence spectra of La0.95-xGdxPO4:Sm3+ phosphors were measured at the excitation wavelength of 400nm, exhibited characteristic emission peaks for Sm3+ at 560, 597, and 643nm. The purely magnetic dipole allowed transition ((4)G(5/2)(6)H(5/2)) at 560nm and partly magnetic dipole transition ((4)G(5/2) H-6(7/2)) at 597nm, responsible for orange-red light, dominated the emission spectra. In contrast to the magnetic dipole transitions, the electric dipole transition ((4)G(5/2)(6)H(9/2)) was found to be relatively less intense confirming high symmetrical crystal environment around Sm3+ in the host lattice. However, with subsequent substitution of Gd3+ at the lanthanide site in the host lattice, the crystal field suffered distortion and thus, influenced the photometric properties. From experimental results, it was evident that these phosphors have suitable Commission International de l'Eclairage (CIE), color correlated temperature (CCT) parameters, appreciable lifetime, and excellent color purity with respect to other reported rare earth ion doped orange-red phosphors. Further, these results could help in the improvisation of their use in optoelectronics especially white LEDs, photovoltaic cells and other strategic applications