Spectroscopic properties of $\gamma$-irradiated Fe$_{m}$O$_{n}$–SiO$_{2}$ composite nanoparticles

The colloidal solutions and deposited layers of Fe$_{m}$O$_{n}$–SiO$_{2}$ composite particles were studied. The colloidal solutions were prepared by precipitation of Fe$_{m}$O$_{n}$ on the surface of porous silicon dioxide particles synthesized from a tetraethoxysilane (TEOS) alcohol solution by the sol–gel method. It was found that, in the visible and near-UV ranges of the absorption spectra, there are six bands typical of conglomerates of Fe$_{m}$O$_{n}$ nanoparticles. The investigation of Raman spectra of the samples subjected to laser annealing and $\gamma$-irradiation revealed the phase transitions Fe$_{3}$O$_{4}$ $\to$ $\gamma$-Fe$_{2}$O$_{3}$ $\to$ $\alpha$-Fe$_{2}$O$_{3}$.