Optical absorption edge in α–Fe2O3: The exciton–magnon structure

Transmission spectra of synthetic and natural hematite (α-Fe2O3) crystals are measured at temperatures 10, 25, and 300 K in the wavelength range 500–1100 nm, and the absorption spectra are computed. Pure exciton and exciton–magnon d–d transition bands are revealed, the corresponding wavelengths at 10 K being λ0=1020 nm and λ1=965 nm respectively. The half-widths and oscillator forces are g0=84 cm−1, f0=4×10−9, g1=60 cm−1, f1=1.4×10−7 for 10 K, g0=85 cm−1, f0=5×10−9, g1=110 cm−1, f1=2.1×10−7 for 25 K. The mechanisms of band formation for weakly allowed d–d transitions in hematite are analyzed.