Tuneable optical properties of Fe2O3 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 degrees 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 celcius) we have precursor Ferritin powder and on the other side (700 celcius) 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 Fe2O3 to hematite crystalline phase (alpha-Fe2O3), 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 degrees 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.

Automated summary

The optical properties of a precursor dry Ferritin powder and its iron oxide derivatives were studied using UV-visible spectroscopy. The iron oxide derivatives exhibit significant changes in absorption spectra with annealing temperature, showing a large shift in absorption band edge. Crystallization and thermal destruction of the organic cage are found to be inter-related. The large absorption band edge shift provides a simple approach to tuneable optical properties of iron oxides.