Monodispersed Ce(iv)–Gd(iii)–Eu(iii) oxide phosphors for enhanced red emission under visible excitation

Abstract

A family of Ce_0.95−xGd_xEu_0.05(OH)CO₃·H₂O monodispersed spherical particles of ca. 200 nm with 0 ≤ x ≤ 0.95 was obtained by the urea homogeneous alkalinization method. These precursors were decomposed at 1273 K under an air atmosphere, resulting in ternary spheroidal phosphors obeying the general formula Ce_0.95−xGd_xEu_0.05O_1.975−x/2. Samples with 0.57 ≤ x ≤ 0.95 exhibit a c-type (Ia3) structure related to the Gd₂O₃ lattice, while a F_m3_m-type (CeO₂) one was found for 0 ≤ x ≤ 0.19. For both ternary families, the partial substitution of host cations dramatically decreases the efficiency of the ligand to metal charge transfer (LMCT) based emission, with respect to their binary end members. In contrast, the emission obtained from direct excitation of Eu(III) with visible light is enhanced. For both structures, the binary Ce(IV)–Gd(III) host improved emission with respect to Gd_0.95Eu_0.05O_1.5 and Ce_0.95Eu_0.05O_1.975 samples, achieving an optimum value for the sample Ce_0.23Gd_0.71Eu_0.05O_1.6 with a Ia3 structure.