Lanthanum hydroxycarbonate (LaCO3OH) superstructures [LHS] decorated with carbon spheres are synthesized by a solvent-free, one-pot Reactions under Autogenic Pressure at Elevated Temperature (RAPET) process, dissociating a single lanthanum acetate hydrate (LAH) precursor. The structure of the as-synthesized LHS are studied by powder X-ray diffraction, high-resolution transmission electron microscopy, morphology by field-emission scanning electron microscopy, and the composition by energy dispersive X-ray analysis, elemental mapping, as well as FT-IR spectroscopy. The photoluminescence results showed an emission band centered at 465 nm (lambda = exc. 360 nm) for the hexagonal phase of LHS. The mechanistic elucidation for the fabrication of LaCO3OH decorated with carbon spheres is developed on the basis of obtained thermal [TGA and DTA] data on initial LAH reactant.