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

Transmission spectra of synthetic and natural hematite (alpha-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 lambda(0) = 1020 nm and lambda(1) = 965 nm respectively. The half- widths and oscillator forces are g(0) = 84 cm(-1), f(0) = 4 X 10(-9), g(1) = 60 cm(-1), f(1) = 1.4 X 10(-7) for 10 K, g(0) = 85 cm(-1), f(0) = 5 X 10(-9), g(1) = 110 cm(-1), f(1) = 2.1 X 10(-7) for 25 K. The mechanisms of band formation for weakly allowed d-d transitions in hematite are analyzed. (C) 1998 American Institute of Physics. [S1063-777X(98)00610-0]