Features of spectral properties of Sm3 + complexes with dithia- and diselenophosphinate ligands

The samarium complexes Sm(S₂PPh₂)₃(THF)₂ (1) and Sm(Se₂PPh₂)₃(THF)₂ (2) with soft-donor dithia- and diselenophosphinate ligands were synthesized and their photophysical properties were studied in detail. Both complexes displayed the metal-centered photoluminescence (PL) in visible and NIR regions corresponding to ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2, 13/2, 15/2), ⁶F_J (J = 1/2, 3/2, 5/2, 7/2, 9/2, 11/2) f-f transitions of Sm^{3 +}. Luminescence decay curves exhibit an initial short build-up region and can be described by double or triple exponential function owing to multiphonon relaxation from the ⁴F_3/2 energy level to the ⁴G_5/2 one and reversible energy transfer from the Sm^{3 +} excited states to the triplet (³T₁) state of phosphinate ligand. A Judd-Ofelt analysis was performed to estimate PL quantum efficiency (QE), branching ratios (β) and induced-emission cross section (σ_em) of the compounds obtained. It was found that the Judd-Ofelt parameter Ω₂ of 1 is significantly greater than that of 2. This feature is responsible for large values of β (50.98%) and σ_em (4.29 × 10^{- 21} cm²) which suggest 1 as a good candidate for the development of samarium doped polymethylmethacrylate (PMMA) laser medium acting on the ⁴G_5/2 → ⁶H_9/2 transition at 645 nm. The estimated room-temperature PL QE of 1 and 2 equals to 1.9 and 0.17%, respectively.