EN
A survey of the physical properties of solid state materials activated with d^{2}, d^{3} and d^{8} transition metal ions is presented in the context of tunable laser operation. An emphasis is put on common characteristics of all three systems, like a strong electron-phonon coupling and similar electronic structures. The conditions necessary to obtain a tunable operation and to avoid an overlap of the excited state absorption and emission are formulated. It is shown that the d^{3} configuration system has the largest range of allowed values of the crystal field parameter 10Dq.