| Summary: | New 3D micro-nanostructured composite materials have been synthesised. These materials comprise SiO<sub>2</sub>/CaCO<sub>3</sub>/C<sub>org</sub>/NdVO<sub>4</sub>NPs and SiO<sub>2</sub>/CaO/C<sub>org</sub>/NdVO<sub>4</sub>NPs, exhibiting strong upconversion luminescence. The synthesis was accomplished by metabolically doping diatom cells with neodymium and vanadium. Subsequently, the biomass of these doped diatoms was subjected to pyrolysis at 800 °C. The morphology, structure, and physicochemical properties of the doped diatom biomass as well as dried (SiO<sub>2</sub>/CaCO<sub>3</sub>/C<sub>org</sub>/NdVO<sub>4</sub>NPs) and pyrolysed (SiO<sub>2</sub>/CaO/C<sub>org</sub>/NdVO<sub>4</sub>NPs) samples were characterised using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), thermal analysis (TG), and fluorescence spectroscopy (FS). Studies have shown that the surface of diatom shells is covered with trigonal prismatic nanocrystallites (nanoparticles) of NdVO<sub>4</sub> with dimensions of 30–40 nm, forming the crystallite clusters in the form of single-layer irregular flakes. The synthesised composites produced intense anti-Stokes fluorescent emission in the visible region under xenon lamp excitation in the near-infrared (λ<sub>ex</sub> = 800 nm) at room temperature in an ambient atmosphere. Such materials could be attractive for applications in solar spectrum conversion, optical sensing, biosensors, or photocatalysts.
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