Cathodo- and photoluminescence emission of a natural Mg-Cr carbonate layered double hydroxide

Abstract Spectral emission of a natural layered double hydroxide (LDH) studied by cathodo- and photoluminescence (PL), displays complex glow curves with wavebands that could be attributable to (i) the paramagnetic Non-bridging Oxygen Hole Center defects (peaked at 330 nm), (ii) F o centers (oxygen vacancies trapping two electrons) associated with O vacancy-hole centers and Me–O bonding defects and dehydroxylation process (in the range of 360–500 nm), (iii) presence of Mn 2+ (0.15%) substituting Mg 2+ ions (530–640 nm) and (iv) a red-IR band mainly associated with Cr and Fe point defects. The presence of Cr 3+ ion activators induces characteristic PL emission peaks in the red-infrared region at 681, 688 and 696 nm linked to 2 E →  4 A 2 transitions. The sample (Mg 6 Cr 2 CO 3 (OH) 16 ·4H 2 O) previously characterized by environmental scanning electron microscope, X-ray diffraction, and X-ray fluorescence indicates that this natural hydrotalcite-like compound is associated with hydroxyl-rich silicates (nimite and clinochlore) and Mg-Fe carbonate and Ni-Fe carbonate LDH (pyroaurite and reevesite).