Abstract
In the present work, Cr-substituted Mg(3)Al(1-x)Cr(x) layered double hydroxides (LDHs) were synthesised through the phase conversion of sol-gel-derived mixed-metal oxides in an aqueous medium. The chromium substitution level in the range of 1 to 25 mol% was investigated. It was demonstrated that all synthesised specimens were single-phase LDHs. The results of elemental analysis confirmed that the suggested synthetic sol-gel chemistry approach is suitable for the preparation of LDHs with a highly controllable chemical composition. The surface microstructure of sol-gel-derived Mg(3)Al(1-x)Cr(x) LDHs does not depend on the chromium substitution level. The formation of plate-like agglomerated particles, which consist of hexagonally shaped nanocrystallites varying in size from approximately 200 to 300 nm, was observed. Optical properties of the synthesised Mg(3)Al(1-x)Cr(x) LDHs were investigated by means of photoluminescence. All Cr-containing powders exhibited characteristic emission in the red region of the visible spectrum. The strongest emission was observed for the sample doped with 5 mol% Cr(3+) ions. However, the emission intensity of samples doped with 1-10 mol% Cr(3+) ions was relatively similar. A further increase in the Cr(3+) ion concentration to 25 mol% resulted in severe concentration quenching.