Selective Laser Spectroscopy of the Bixbyite-Type Yttrium Scandate Doped by Rare-Earth Ions

Yttrium scandate crystals doped by Nd³⁺ and Tm³⁺ ions have been successfully grown in the form of fibers using the laser-heated pedestal growth (LHPG) technique. The selective laser spectroscopy methods have identified and distinguished three distinct types of optically active centers associated with Nd³⁺ and Tm³⁺ ions. The substitution of Y³⁺ and Sc³⁺ for rare-earth ions in the C₂ structural site leads to the formation of two distinct basic long-time centers. In Nd³⁺:YScO₃, another type of center (a short-lifetime one) is formed known as the Nd³⁺-Nd³⁺ aggregate pair. This center arises from the substitution of Y³⁺ or Sc³⁺ for Nd³⁺ cation in the adjacent MO₆ polyhedra that share an edge. In Tm³⁺:YScO₃, the third optical center is formed as a result of the substitution of Y³⁺ or Sc³⁺ for Tm³⁺ in the MO₆ octahedra with the C_3i site symmetry. The fluorescence decay lifetimes of Nd³⁺ and Tm³⁺ ions in the YScO₃ crystal structure have been accurately measured and estimated. A Stark level diagram illustrating the splitting of ⁴F_3/2, ⁴I_11/2, and ⁴I_9/2 multiplets of Nd³⁺ ions has been constructed to show features of the active optical centers with the C₂ site symmetry.