corundum, synthetic corundum.7, flux, color.4, gems

In our studies of the Electron Spin Resonance (ESR) spectra of natural sapphires (Troup and Hutton, 1983), we observed in many cases a large number of small lines covering a wide magnetic field range; an example is given in Figure 1. The hypotheses we put forward to explain these lines were: (a) that they could be due to pairs of Cr³⁺ or Fe³⁺ ions; (b) that they could be due to radiation damage; and (c) that they could be due to Mn²⁺. Although the Spin-Hamiltonian (ESR spectral parameters and behaviour) of Mn²⁺ in sapphire have been published previously (Low and Suss, 1960; Folen, 1962), no illustrations of spectra were given. It would have been possible to calculate the appearance of the spectra, but this involves assumptions about line-shapes. Accordingly, it was decided to synthesize some Mn²⁺-doped sapphire in order to record the ESR spectra and compare the appearance and line positions with the extended, small-line spectra mentioned above.