Phonon coupling of Cr3+ ions in Cs2NaAlF6 crystals

We have studied the influence of the electron-lattice coupling on the luminescence quantum yield for Cr3+ ions in a Cs2NaAlF6 crystal. For this purpose, we analyze the absorption and emission spectra of Cr3+ ions by means of the configurational coordinate model in the harmonic approximation. We have found the energy of the breathing phonon associated to Cr3+ ions in this host. In our findings we explain the high value of luminescence quantum yield reported previously (near to 70%), if we take into account the uncoupling between the breathing phonon and the normal modes associated to the bulk vibration. The Cr3+:Cs2NaAlF6 crystals promise to be a potential efficiency tunable laser device in the near infrared (700–900 nm) spectral range.