TetragonalNi+ions in x-ray-irradiatedKMgF3:Ni

An EPR study of three types of ${\mathrm{Ni}}^{+}$ centers created by x-ray irradiation of ${\mathrm{KMgF}}_3$:Ni single crystals is reported. The three centers have tetragonal symmetry. One of them (${\mathrm{Ni}}^{+}$-I) can be created both by 77-K and room-temperature irradiation but its EPR signal can only be observed at temperatures lower than 30 K. The other two (${\mathrm{Ni}}^{+}$-II and ${\mathrm{Ni}}^{+}$-III) are not detected in the 77-K-irradiated sample and their EPR spectra can be observed even at 300 K. The components of the g tensor of these centers are $g_{?}$=2.657±0.002 and $g_{\perp }$=2.137±0.005 for ${\mathrm{Ni}}^{+}$-I, $g_{?}$=2.578±0.002 and $g_{\perp }$=2.108±0.002 for ${\mathrm{Ni}}^{+}$-II, and $g_{?}$=2.545±0.005 and $g_{\perp }$=2.085±0.005 for ${\mathrm{Ni}}^{+}$-III.