| Summary: | In the present work, Cr-substituted Mg<sub>3</sub>Al<sub>1−x</sub>Cr<sub>x</sub> 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<sub>3</sub>Al<sub>1−x</sub>Cr<sub>x</sub> 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<sub>3</sub>Al<sub>1−x</sub>Cr<sub>x</sub> 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<sup>3+</sup> ions. However, the emission intensity of samples doped with 1–10 mol% Cr<sup>3+</sup> ions was relatively similar. A further increase in the Cr<sup>3+</sup> ion concentration to 25 mol% resulted in severe concentration quenching.
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