S 1 Level of Pr3+ in Crystal Matrices and Energy-Level Parameters for the 4f2 Configuration of Pr3+ in LaF3

The absorption spectrum of Pr³⁺ in LaF₃, LaCl₃, CaF₂, Pr(Y)Cl₃·6H₂O, and Pr₂(SO₄)₃·8H₂O was investigated. Evidence for the ${}^1{S}_0$ level in Pr³⁺:LaF₃ at 46 986 cm⁻¹ is presented; this level was not observed directly in absorption in any of the other matrices studied. An analysis of the 13 observed levels in Pr³⁺:LaF₃, based in part upon a re‐examination of the experimentally observed crystal‐field components of certain levels, gave the following electrostatic, spin–orbit, and configuration‐interaction parameters: $E^1{\text{\hspace{0.17em}=\hspace{0.17em}4559.0, E}}^2{\text{\hspace{0.17em}=\hspace{0.17em}21.954, E}}^3{\text{\hspace{0.17em}=\hspace{0.17em}467.75, ζ}}_{\text{4f}}\text{\hspace{0.17em}=\hspace{0.17em}744.44, α\hspace{0.17em}=\hspace{0.17em}15.294, β\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}669.02, γ\hspace{0.17em}=\hspace{0.17em}1411.8}$ , with an rms deviation= 33 cm⁻¹.