Propriedades fotoluminescentes do 𝑍𝑛2𝑇𝑖𝑂4 dopado com íons divalentes de cobalto

Abstract

Zinc orthotitanate samples (Zn2TiO4) containing Co2+ ions as substitutional impurities were prepared by the solid state reaction technique using the reagents zinc oxide (ZnO), titanium dioxide (TiO2) and cobalt carbonate (CoCO3). The obtained samples were characterized with X-Ray Fluorescence, X-Ray Diffraction, Photoluminescence and Photoluminescence Excitation techniques. The X-ray Diffraction data were adjusted using the Rietveld method for the refinement of the structures with the determination of the phases and obtaining the respective crystalline parameters. The analysis of the optical measurements using the Crystal Field Theory provided information about the energy states involved in the transitions, the energy parameters of the dopant-ligand system and the crystallographic symmetry of the site of occupation of the divalent Cobalt ions. Photoluminescence data indicate that Co2+ ions probably occupy only one type of tetrahedral site. The transition assignment 4T1(4P) → 4A2 (4F) for the bands with barycentres at 714 nm, 711 and 712 nm for samples doped with 0.1%, 0.5% and 1% Co2+, respectively, agrees with emission decay curves, since the allowed transitions have a short radiative life of ~ 10 μs. It is possible that the Co2+ ions occupy octahedral sites in the zinc orthotitanate, since the Zn2+ ions that are replaced by Co2+ are randomly distributed in the tetrahedral and octahedral sites of the inverse spinel structure of the studied system, but instrumental limitations did not allow the verification of this possibility. To our knowledge, this is the first work where the levels of Co2+ tetrahedral energy in the zinc orthotitanate are studied and the energy parameters are calculated. The experimental methods used allowed to qualify the system as a promising active medium of tunable radiation.