We report on the ground-and excited-state properties of Fe 3+ centers in hydrothermally and chemical-vapor-transport grown single ZnO crystals studied by continuous-wave electron-paramagnetic resonance (EPR) under dark and laser-illuminated conditions, pulsed-EPR and magneto-photoluminescence. By use of EPR experiments, the fine-structure parameters of the Fe 3+ spin Hamiltonian are determined. Three types of charge-compensated Fe 3+ centers are identified and the charge conversion from Fe 2+ to Fe 3+ is highlighted. The magneto-optical studies of the Zeeman components of the spin-forbidden electric-dipole transitions from excited T 1 4 (G) to ground A 1 6 (S 6) states of the Fe 3+ center indicate the trigonal symmetry of the fine structure of the lowest Γ 8 (T 1 4) excited state. The energy positions of the Zeeman components are measured in the external magnetic field of 8 T rotated in (1 2 10) and …