Tuneable optical properties of Fe 2 O 3 magnetic nanoparticles synthesized from Ferritin

The optical properties of a precursor dry Ferritin powder and its iron oxide derivatives were studied using UV–visible spectroscopy. The iron oxide derivatives were synthesized by applying controlled heat treatment up to 700 °C. The optical properties show dramatic variation in absorption spectra through a large shift in absorption band edge as a function of annealing temperature. On one side (40 ℃) we have precursor Ferritin powder and on the other side (700 ℃) a crystalline hematite phase along with disordered phases at intermediate temperatures. Energy dispersive x-ray (EDX) analysis and XRD reveal that crystallization and thermal destruction of organic cage are inter-related. As ferrihydrite complexes inside the Ferritin cavity go through solidification from amorphous Fe 2 O 3 to hematite crystalline phase (α-Fe 2 O 3 ), the heterogeneity of electronic excitation processes occurs through ligand-to-metal charge transfer (LMCT), pair excitation and ligand field (d-d) transition. Strong magnetic induction in the intermediate range (400–500 °C) was associated with the enhancement of the pair excitation process. As the material changes phases due to annealing, a large absorption band edge shift from 2.65 to 1.28 eV, a total red shift of 1.37 eV, provides a simple approach to tuneable optical properties of iron oxides. Graphical abstract Top panel shows the variation of optical band gap, whereas bottom panel describe the weight percentage variation of different elements with annealing temperature. Middle panel presents the entire theme in form of a sketch of the process related to the synthesis of different phases.