Optical absorption and electron paramagnetic resonance (EPR) measurements were used to determine the presence of different vanadium charge states and to estimate their respective concentrations. Absorption peaks attributed to V3+ and V4+, intra 3d-shell transitions, respectively, as well as V3+ and V4+ hyperfine octets were measured in samples cut from a vanadium doped and a vanadium/boron co-doped crystal. Results were compared to chemical analysis and electrical measurements. As a result, the V3+ and V4+ features were found to correlate with the respective concentration of vanadium in different charge states.