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

Abstract

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.