Spectroscopy, crystal-field, and transition intensity analyses of the C3v(O2−) centre in Er3+ doped CaF2 crystals

Erbium ions in crystals show considerable promise for the technologies that will form the backbone of future networked quantum information technology. Despite advances in leveraging erbium’s fibre-compatible infrared transition for classical and quantum applications, the transitions are, in general, not well understood. We present detailed absorption and laser site-selective spectroscopy of the C${}_{\mathrm{3v}}$(O${}^{2-}$) centre in CaF${}_2$:Er${}^{3+}$ as an interesting erbium site case study. The ⁴I${}_{15/2}$Z${}_1{\to }^4$I${}_{13/2}$Y${}_1$ transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the ¹⁶⁷Er isotope. A parametrized crystal-field Hamiltonian is fitted to 34 energy levels and the two ground state magnetic splitting factors. The wavefunctions are used to perform a transition intensity analysis and electric-dipole parameters are fitted to absorption oscillator strengths. Simulated spectra for the ⁴I${}_{11/2}{\to }^4$I${}_{15/2}$ and ⁴I${}_{13/2}{\to }^4$I${}_{15/2}$ inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The ⁴I${}_{13/2}$ excited state lifetime is 25.0 ms and the intensity calculation is in excellent agreement with this value.