Indofluorides in the AMF3-InF3 systems (A=K, Rb, Cs and M=Mg, Zn) and optical properties of Cr:K0.38Mg0.38In0.62F3

Among the fluorides disclosed in the AMF₃-InF₃ systems (A=K, Rb, Cs/M=Mg, Zn), the most favorable material for optical applications in relation with the optical quality of its crystals is K_0.38Mg_0.38In_0.62F₃ (KMI), a distorted monoclinic Magnéli-bronze, which crystals are grown from the melt. Cr³⁺ introduced in this host is optically characterized by optical spectroscopy. The chromium ions in the single crystals occupy simultaneously centrosymmetric and non-centrosymmetric sites. The broad emission band (⁴T_2 g→⁴A_2 g transition) obtained in the near infrared range is characteristic of a small crystal field effect (Dq=1476 cm⁻¹). Crystal field analysis leads to a very good agreement between calculated and experimentally observed energy levels. Furthermore, dips observed in the absorption at about 15370 cm⁻¹ are related to the calculated mixing between the wave functions, connected with the ⁴T_2 g (⁴F) and ²E_g (²G) and ²T_1 g (²G) electronic levels.