Transparent Lu_0.8Sc_0.2BO₃:Ce single crystals doped with different forms of cerium [CeF₃, CeO₂ or Ce(NO₃)₃] were grown by the Czochralski method. The influence of cerium doping form on the luminescence mechanism, point defect and scintillation efficiency of Lu_0.8Sc_0.2BO₃:Ce was investigated and discussed in detail. We found that the cerium doping form had no influence on the luminescence mechanism and the type of point defects in Lu_0.8Sc_0.2BO₃:Ce host. The underlying reason for the scintillation efficiency discrepancy in these singlecrystall samples was revealed by XANES technique. Based on the Ce L_III-edge XANES spectra, it can be concluded that the Ce³⁺/Ce⁴⁺ ratio in the crystal resulted in the scintillation emission discrepancy. More importantly, our research demonstrates that it is possible to qualitatively identify the cerium oxidation state in single crystal scintillator doped with trace amounts of Ce ions by the XANES method and that the scintillation efficiency of single crystals could be tailored by manipulating the content of the contributed valence state, such as Ce³⁺ for Ce ions.