Some unique laser ions are cobalt ions Co2+, nickel ions Ni2+, and iron ions Fe2+.

A common property of transition metal ions is that the corresponding absorption and laser transition bandwidths are very wide, so a very large gain bandwidth can be obtained. This is due to the strong interaction between electronic transitions and phonons, causing isotropic broadening. Laser-active transition metal ions usually use crystals rather than glasses as host media because crystals are more thermally conductive and the anisotropic broadening of glassy species is also unfavorable.
The most important lasers based on transition metal ion gain media are Ti:Sapphire lasers, but there are also many lasers using chromium-doped gain media, such as Cr4+:YAG or Cr3+:LiSAF. Less common lasers are Co2+:MgF2, Co2+:ZnF2 and Ni2+:MgF2.