The investigation of RE 3+ :YScO3 mixed sesquioxide requires modern methods of selective laser spectroscopy. These methods enable the determination of quantitative features of optical centers and the identification of channels for both radiative and non-radiative energy . Especially this applies to the transfer of excitation energy between the RE 3+ optical centers, which are formed in the YScO3 crystal fiber by substituting the positions of yttrium and scandium. The utilization of selective laser spectroscopy methods will allow for obtaining a complete characterization of the optical properties of RE 3+ impurity center in YScO3 crystal fiber and assessing the potential of this matrix as a laser-active medium.