Synthesis of Er–Yb co-doped MgNb2O6 ceramics and the exploration of their up-conversion photoluminescence and photocatalytic properties

Abstract

Rare earth (RE) doped ceramic materials are now known to offer considerable promise as phosphors, providing avenues for a wide range of applications in the photon domain when synthesized with appropriate compositions and crystal structures. Furthermore, because of the charge carriers (electron-hole pair) that these phosphors contain, they have also the potential for photoluminescence and photocatalysis. This research explores the solid-state synthesis of RE-doped MgNb₂O₆ and the characterization of their upconversion photoluminescence and photocatalytic properties. Three different compositions of the columbite, MgNb₂O₆, MgNb₂O₆–Er, and MgNb₂O₆–Er-Yb were synthesized via solid-state reaction methods. Their crystallographic structures were confirmed to be orthorhombic for all the three compositions, with slight expansion in the RE-doped compositions' bulk volume. Their measured band gap energy (E_g) were 3.93, 4.03, and 4.03 eV, respectively. The room temperature up-conversion photoluminescence spectra of the as-sintered RE-doped ceramic bodies showed two emissions near 543 nm and 674 nm, which corresponded to the transitions of Er³⁺ ions from ²H_11/2 to ⁴I_15/2 and ⁴F_9/2 to ⁴I_15/2, respectively. As proposed by theoretical models, it was confirmed that the photoluminescence intensity is proportional to the nth power of the excitation intensity. This up-conversion photoluminescence was observed as an enhancement in the fluorescent intensity of the Er–Yb co-doped samples, possibly due to the charge transfer process between Yb³⁺ and Er³⁺ ions. The photocatalysis under UV light and adsorption studies for the decolorization of Victoria blue dye were investigated with about 50 % dye removal in the evaluated conditions. The VB dye removal indicated that the RE-doped MgNb₂O₆ Columbite is potentially applicable in environmental remediation.