Spin transition in Co³⁺ by optical absorption and time-resolved spectroscopy under pressure: an appraisal of the different spin states

Abstract

This work investigates the electronic structure of CoF₃ by optical absorption and its relationship with the ground-state spin and the Jahn–Teller (JT) effect exhibited by Co³⁺(d⁶) in octahedral coordination (CoF₆)³⁻. The results are compared with other Co³⁺ fluorides and oxides, where Co³⁺ is high spin (HS) and low spin (LS), respectively. In CoF₃ we detect an absorption band with a doublet structure at 1.89 eV (657 nm) and 1.45 eV (855 nm) at 2.5 GPa, which is associated with the T ⊗ e JT effect on the ⁵T₂ HS ground state. Absorption measurements under pressure have been carried out around the HS–LS (⁵T₂ ↔¹A₁) spin crossover transition in the 0–20 GPa range. We show that the JT effect is stable in a wide pressure range. No sign of intermediate spin (³T_{1, 2} states) is observed in the explored pressure range.

Keywords:

• Co³⁺
• CoF₃
• spin crossover
• intermediate spin
• Jahn–Teller

Acknowledgements

Financial support from the Spanish MEC (Project No MAT2005-00099) and MALTA INGENIO-CONSOLIDER 2010 (Ref. CDS2007-0045) are acknowledged. MNSO thanks the Spanish MEC for a FPU grant (Ref. AP-2004-5954).