ESR study of spin-Hamiltonian parameters and crystal field energy levels for the low C3 symmetry Fe3+ center in green sapphire crystals and powder

Abstract

In this report, Fe3+ impurity ions present in green sapphire (Al3O3) were studied experimentally, by heating a light green sapphire in flowing oxygen atmosphere for 12 h from 1200, 1300, 1400, 1500 and 1600°C, respectively. Electron spin resonance (ESR) spectra in X-band (∼9.45 GHz) were recorded by mounting the crystal with the c-axis perpendicular (θ = 90°) to the magnetic field direction. The spectra were recorded and simulated by a numerical diagonalization of spin Hamiltonian matrix in the range from 0 to 180 degrees for every 15 degrees of rotation angle (φ). In our case, only the last two sets of peaks strongly depend on the rotation angle (φ), and each exhibits C3 symmetry due to two magnetically inequivalent Fe3+ sites in the corundum structure. For polycrystalline ESR spectra, seven main Fe3+ ESR absorption peaks occur at the resonance magnetic fields of 100.20, 310.24, 486.80, 525.00, 550.60, 761.00 and 777.00 mT respectively. Specifically, ESR signals show that the number of paramagnetic Fe3+ ions increase roughly linearly with the heat treating temperature, having the Fe3+/FeRT 3+ ratio ∼1.41 at 1600°C. © World Scientific Publishing Company.