We report on a high-resolution optical and magneto-optical spectroscopy, luminescence, and electron paramagnetic resonance (EPR) studies of yttrium orthophosphate single crystals doped with erbium, which are promising telecom-wavelength materials for applications in quantum electronics and quantum information processing. An observation of the hyperfine structure in optical spectra of
167Er isotope in
Er:YPO4 is presented. Energies and symmetries of 40 crystal-field levels of
Er3+ in
Er:YPO4 and
g factors of some of them were determined and successfully modeled on the basis of crystal-field calculations. The obtained set of crystal-field parameters was used in modeling the hyperfine structure observed in the optical and EPR spectra of
Er:YPO4 single crystals.
Electron paramagnetic resonance (EPR) spectroscopy of rare earth ions in crystals is a powerful tool to analyze the hyperfine structure of the rare earth ground state. This can be useful for coherent spectroscopy and quantum information applications where the hyperfine structure of the electronic levels is used. In this work, we give a detailed analysis of the hyperfine structure of the ground state
[4I15∕2(0)] of
Er3+ ions in
Y2SiO5. The electronic Zeeman, hyperfine, and quadrupole matrices are obtained from angular variations of the magnetic field in three orthogonal crystal planes. An excellent agreement is obtained between experimental and simulated magnetic field positions and relative intensities of EPR lines.
High-resolution spectroscopy (as fine as $0.01\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$) was applied to a
1mol holmium-doped single crystal of yttrium aluminum tetraborate with the purpose of studying the hyperfine splitting of
Ho3+ energy levels of interest for possible quantum manipulation media. The hyperfine structure was clearly revealed for a high number of lines in a wide wave number range (up to $\ensuremath{\simeq}21\phantom{\rule{0.2em}{0ex}}300\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$) and for a large number of multiplets. Several different hyperfine patterns were monitored, differing in the number of lines, in their separation, and in their relative statistical weight. These features were all understood by a crystal-field model, whose results are in very good agreement with experiments and account for the involved level symmetry, the type of transitions (electric and magnetic dipole allowed), the possibility of a second-order (pseudoquadrupolar) hyperfine coupling between close levels, and a slight distortion of the local
D3 symmetry in Ho-occupied sites.
When introduced as dopants into
Y2O3,
Er3+ ions replace
Y3+ ions at two crystallographic sites of
C2 and
C3i point symmetries. The
C3i site is particularly interesting, given that the inversion symmetry prohibits static electric-dipole moments and electric-dipole transitions, resulting in 1.5 \textmu{}m optical transitions characterized by purely magnetic-dipole properties. Employing $\mathrm{E}{\mathrm{r}}^{3+}\phantom{\rule{4pt}{0ex}}^{4}I_{15/2}\ensuremath{\leftrightarrow}^{4}I_{13/2}$ transitions, we examined the inherent
C3i site of
Er3+ in
Y2O3 for its potential in quantum information science and spectral hole burning applications. Our approach involved absorption and site-selective fluorescence spectroscopy to discern
Er3+ energy levels and revealed an excited-state lifetime of 14.6 ms. High-resolution laser spectroscopy at 3.7 K indicated an inhomogeneous linewidth of 1.3 GHz in our sample. Orientation-dependent Zeeman laser absorption spectroscopy facilitated the determination of the full
g tensors for both the ground and excited states, confirming the
C3i site assignment. Furthermore, it identified a suitable magnetic field direction for mitigating decoherence, a finding corroborated through two-pulse photon echo spectroscopy. Our study presents photon echo coherent transient measurements related to magnetic-dipole-allowed rare-earth ion transitions at the
C3i site. The observed decoherence, attributed to spectral diffusion arising from $\mathrm{E}{\mathrm{r}}^{3+}\text{\ensuremath{-}}\mathrm{E}{\mathrm{r}}^{3+}$ magnetic-dipole interactions, underscores the complex spin dynamics at play in systems with multiple inequivalent dopant sites. Coupled with the practicality of telecom laser wavelengths, our investigation highlights the promise of magnetic-dipole transitions in advancing quantum information science and spectral hole burning applications.
We report on the development and application of a parametrized crystal-field model for both
C1 symmetry centers in trivalent erbium-doped
Y2SiO5. High-resolution Zeeman and temperature dependent absorption spectroscopy was performed to acquire the necessary experimental data. The obtained data, in addition to the ground
(4I15/2Z1) state and exited
(4I13/2Y1) state Zeeman and hyperfine structure, were simultaneously fitted in order to refine an existing crystal-field interpretation of the
Er3+:
Y2SiO5 system. We demonstrate that it is possible to account for the electronic, magnetic, and hyperfine structure of the full
4f11 configuration of
Er3+:
Y2SiO5 and further, that it is possible to predict both optical polarization behavior and high magnetic field hyperfine structure of transitions in the $1.5\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ telecommunications band.
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
3v(O
2−) centre in CaF
2:Er
3+ as an interesting erbium site case study. The
4I
15/2Z
1→4I
13/2Y
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→4I
15/2 and
4I
13/2→4I
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.