Structural Characterization and Photoluminescent Properties of (La_1–<i>x</i>Sm<i>_x</i>)₂Ti₂O₇ Solid Solutions Synthesized by a Sol–Gel Route

Abstract

Abstract A series of compounds with the general formula (La 1– x Sm x ) 2 Ti 2 O 7 (0 ≤ x ≤ 1.0) has been synthesized by a sol–gel method and characterized by XRD, Raman spectroscopy, and scanning electron microscopy (SEM). These compounds are structurally isomorphic to perovskite‐type La 2 Ti 2 O 7 until a substitution rate of x = 0.8. Above this substitution rate ( x &gt; 0.8), a biphasic mixture is obtained between the substituted perovskite layered phase and the pyrochlore Sm 2 Ti 2 O 7 phase. The unusual phosphor (La 1– x Sm x ) 2 Ti 2 O 7 has been elaborated and its luminescent properties were investigated for low rates of substitution. The emission and excitation spectra were used to study the luminescent properties. The (La 1.9 Sm 0.1 ) 2 Ti 2 O 7 powders emit bright red­–orange lightunder UV excitation. The emission properties show thatLa 2 Ti 2 O 7 is a suitable host where the La 3+ ions can be substituted by other trivalent lanthanide ions that induce luminescence properties in the visible region and lead to phosphor materials. The electronic structure calculations of (La 1.9 Sm 0.1 ) 2 Ti 2 O 7 shows that this compound is an insulator with a band gap of about 2.77 eV. The valence band mainly consists of oxygen states with hybridized titanium and samarium states; whereas, the conduction band mainly consists of titanium states with hybridized lanthanum and samarium states.