Electronic Spectra of Cs₂NaYb(NO₂)₆: Is There Quantum Cutting?

The crystal structure and electronic spectra of the T_h symmetry hexanitritoytterbate(III) anion have been studied in Cs₂NaY_0.96Yb_0.04(NO₂)₆, which crystallizes in the cubic space group Fm3. The emission from Yb³⁺ can be excited via the NO₂^- antenna. The latter electronic transition is situated at more than twice the energy of the former, but at room temperature, one photon absorbed at 470 nm in the triplet state produces no more than one photon emitted. Some degree of quantum cutting is observed at 298 K under 420 nm excitation into the singlet state and at 25 K using excitation into either state. The quantum efficiency is ∼10% at 25 K. The energy level scheme of Yb³⁺ has been deduced from excitation and emission spectra and calculated by crystal field theory. New improved energy level calculations are also reported for the Cs₂NaLn(NO₂)₆ (Ln = Pr, Eu, Tb) series using the f-Spectra package. The neat crystal Cs₂NaYb(NO₂)₆ has also been studied, but results were unsatisfactory due to sample decomposition, and this chemical instability makes it unsuitable for applications.