Structural and photoluminescence characteristics of Sm3+ activated RE2Ti2O7 (RE = Gd, La) as orange-red emitting phosphors

Abstract

A series of solid solutions with the general formula (Gd1−xSmx)2Ti2O7 (0 ≤ x ≤ 1) and (La1−xSmx)2Ti2O7 (x = 0 and 0.5) were prepared by traditional solid state method at 1200°C under air atmosphere. The X-ray powder diffraction, scanning electron microscopy (SEM) and Raman spectroscopy analysis were performed to confirm the phase purity and to characterize the structure of the as-synthesized materials. Rietveld refinement of XRD showed that (Gd1−xSmx)2Ti2O7 solid solutions crystallize in the pyrochlore structure (Fd3m, Z = 8) while (La1−xSmx)2Ti2O7 (x = 0 and 0.5) oxides adopt the layered-perovskite one (P21, Z = 4). The photoluminescence excitation, the emission spectra and the concentration effect were investigated. The excitation spectra of the phosphors show a broad charge-transfer band in the short wavelength region and several sharp lines in the longer wavelength region originated from Sm3+, which indicates that these phosphors can be effectively excited by UV chips. The Gd1.20Sm0.80Ti2O7 phosphor exhibits the strongest emission among (Gd1−xSmx)2Ti2O7 (0 ≤ x ≤ 0.50) solid solutions after the excitation at 292nm and could be useful for developing new luminescent materials. On the basis of PL spectroscopy, it was inferred that the Sm3+ ion stabilizes at Gd3+ site with inversion symmetry in the first luminescent material Gd1.20Sm0.80Ti2O7, whereas most of Sm3+ ion occupies La3+ site without inversion symmetry in the second luminescent material LaSmTi2O7. The energy bands gap were also determined using UV–visible diffuse reflectance spectroscopy. Both Gd1.20Sm0.80Ti2O7 and LaSmTi2O7 phosphors show a strong orange-red emission in the visible range, which may be useful for display technologies and LED applications.