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Physical review. B, Condensed matter

Site-selective spectroscopy of Ho3+ ions in CsCdBr3 crystals

Marjorie Mujaji, Glynn D. Jones, R. W. G. Syme

Published Jul 1, 1993• 36 citations
Publisher

Abstract

With the use of laser-selective excitation, an extensive set of energy levels has been established for the principal ${\mathrm{Ho}}^{3+}$ dimer center in ${\mathrm{CsCdBr}}_{3}$:${\mathrm{Ho}}^{3+}$ crystals. The observed splittings of around 2 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ of the transitions to or from energy levels assigned as having ${\ensuremath{\gamma}}_{3}$ symmetry under ${\mathit{C}}_{3\mathit{v}}$ symmetry is indicative of deviations of the ${\mathrm{Ho}}^{3+}$ ion-site symmetry from exact ${\mathrm{C}}_{3\mathit{v}}$ symmetry. As for the previously studied ${\mathrm{Er}}^{3+}$ pair center in ${\mathrm{CsCdBr}}_{3}$, the ${\mathrm{Ho}}^{3+}$ pair center exhibits strong upconversion fluorescence with up to one-third the intensity of the direct fluorescence under cw laser excitation of the $^{5}$${\mathit{I}}_{8}$${\ensuremath{\rightarrow}}^{5}$${\mathit{S}}_{2}$ transition in the green and up to one-fifteenth the intensity for comparable cw laser excitation of the $^{5}$${\mathit{I}}_{8}$${\ensuremath{\rightarrow}}^{5}$${\mathit{F}}_{5}$ transition in the red. Additional small splittings of up to 0.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ appear for the sharper transitions and are attributed to the ion-pair interaction. Energy levels are also reported for three varieties of minority centers with one of these centers being present in both 0.3% and 0.1% ${\mathrm{Ho}}^{3+}$ crystals, another in 0.01% ${\mathrm{Ho}}^{3+}$ crystals and the third in ${\mathrm{Na}}^{+}$ codoped crystals. Crystal-field analyses are reported for the principal dimer center and two of the minority centers. Fluorescence lifetimes were determined for several transitions of the dimer center and used to infer energy-transfer rates. Preliminary high-resolution results are reported for the excitation profiles of the two lowest-energy $^{5}$${\mathit{I}}_{8}$${\ensuremath{\rightarrow}}^{5}$${\mathit{F}}_{5}$ transitions that show complex hyperfine patterns.

DOI
10.1103/physrevb.48.710

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Laser-selective excitation and optical-absorption techniques have been used to establish comprehensive sets of energy levels for both the ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$ and hydrogenic varieties of the tetragonal symmetry (${\mathit{C}}_{4\mathit{v}}$) centers in ${\mathrm{SrF}}_{2}$ and ${\mathrm{CaF}}_{2}$. Polarization of the various spectral lines was used to determine the symmetry labels of many of the energy levels. Reversals of the ordering of some levels between ${\mathrm{SrF}}_{2}$ and ${\mathrm{CaF}}_{2}$ are found and, in particular, the two lowest levels (${\mathit{D}}_{1}$ and ${\mathit{D}}_{2}$) of the $^{1}$${\mathit{D}}_{2}$ multiplet, which are the originating levels for many of the observed emission transitions, have reversed-symmetry label assignments in ${\mathrm{SrF}}_{2}$ and ${\mathrm{CaF}}_{2}$. Differences were found between the ground-state Zeeman splittings for the ${\mathit{C}}_{4\mathit{v}}$ ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$ and ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ centers for both ${\mathrm{SrF}}_{2}$ and ${\mathrm{CaF}}_{2}$. Fluorescence lifetimes of the ${\mathit{C}}_{4\mathit{v}}$ hydrogenic centers show a strong dependence on the particular charge-compensating ion present through nonradiative decay processes involving the respective local mode phonons. The upconversion spectra observed for ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$, ${\mathit{T}}^{\mathrm{\ensuremath{-}}}$, and ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ varieties of the ${\mathit{C}}_{4\mathit{v}}$ centers in ${\mathrm{SrF}}_{2}$ and for the ${\mathit{C}}_{4\mathit{v}}$ ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$ center in ${\mathrm{CaF}}_{2}$ are all consistent with excitation of specific subsets of nearby ${\mathit{C}}_{4\mathit{v}}$ centers.

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The observation of two-photon absorption by a very efficient up-converted emission is reported for ${\mathrm{Ho}}^{3+}$ in Ca${\mathrm{F}}_{2}$, Sr${\mathrm{F}}_{2}$, and Cd${\mathrm{F}}_{2}$ with both cw- and pulse-laser excitations. The two-photon excitation spectra are found to be highly structured and consist of two bands: The band $A$ is excited by the dye-laser photons of frequencies 15 400-15 700 ${\mathrm{cm}}^{\ensuremath{-}1}$: The band $B$ is excited by the dye-laser photons of frequencies 15 800-16 400 ${\mathrm{cm}}^{\ensuremath{-}1}$. No one-photon absorption is observed for ${\mathrm{Ho}}^{3+}$ in the above lattices at twice these frequencies. Studies of concentration dependence, temperature dependence, and dependence on the pulse repetition rate are used for the assignment of the band. The investigation shows that the two bands $A$ and $B$ arise from two different modes of two-photon excitation. The band $A$ is assigned to arise from a sequential (stepwise) two-photon excitation $^{5}I_{8}\ensuremath{\rightarrow}^{5}F_{5}\ensuremath{\rightarrow}^{5}D_{2}$. The band $B$ is assigned to arise from the direct two-photon absorption $^{5}I_{8}\ensuremath{\rightarrow}^{3}L_{8}$. Our results are in agreement with the prediction of the Judd-Ofelt theory of lanthanide transition intensities.

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Spectroscopy, crystal-field, and transition intensity analyses of the C 3v (O 2− ) centre in Er 3+ doped CaF2 crystals

M. D. Moull, Jamin L.B. Martin, T.G.M. Newman +4 more

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 4 I 15 / 2 Z 1 → 4 I 13 / 2 Y 1 transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the 167 Er 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 4 I 11 / 2 → 4 I 15 / 2 and 4 I 13 / 2 → 4 I 15 / 2 inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The 4 I 13 / 2 excited state lifetime is 25.0 ms and the intensity calculation is in excellent agreement with this value. • Detailed spectroscopic study of the C 3v (O 2 − ) Centre in CaF 2 :Er 3 + . • Crystal-field fit to 34 energy levels and ground-state magnetic splitting. • Transition intensity analysis for the technologically relevant infrared transitions.

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With the use of laser-selective excitation, an extensive set of energy levels has been established for the principal Ho3+{\mathrm{Ho}}^{3+}Ho3+ dimer center in CsCdBr3{\mathrm{CsCdBr}}_{3}CsCdBr3​:Ho3+{\mathrm{Ho}}^{3+}Ho3+ crystals. The observed splittings of around 2 cm\ensuremath−1{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}cm\ensuremath−1 of the transitions to or from energy levels assigned as having \ensuremathγ3{\ensuremath{\gamma}}_{3}\ensuremathγ3​ symmetry under C3v{\mathit{C}}_{3\mathit{v}}C3v​ symmetry is indicative of deviations of the Ho3+{\mathrm{Ho}}^{3+}Ho3+ ion-site symmetry from exact C3v{\mathrm{C}}_{3\mathit{v}}C3v​ symmetry. As for the previously studied Er3+{\mathrm{Er}}^{3+}Er3+ pair center in CsCdBr3{\mathrm{CsCdBr}}_{3}CsCdBr3​, the Ho3+{\mathrm{Ho}}^{3+}Ho3+ pair center exhibits strong upconversion fluorescence with up to one-third the intensity of the direct fluorescence under cw laser excitation of the ^{5}$${\mathit{I}}_{8}$${\ensuremath{\rightarrow}}^{5}$${\mathit{S}}_{2} transition in the green and up to one-fifteenth the intensity for comparable cw laser excitation of the ^{5}$${\mathit{I}}_{8}$${\ensuremath{\rightarrow}}^{5}$${\mathit{F}}_{5} transition in the red. Additional small splittings of up to 0.5 cm\ensuremath−1{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}cm\ensuremath−1 appear for the sharper transitions and are attributed to the ion-pair interaction. Energy levels are also reported for three varieties of minority centers with one of these centers being present in both 0.3% and 0.1% Ho3+{\mathrm{Ho}}^{3+}Ho3+ crystals, another in 0.01% Ho3+{\mathrm{Ho}}^{3+}Ho3+ crystals and the third in Na+{\mathrm{Na}}^{+}Na+ codoped crystals. Crystal-field analyses are reported for the principal dimer center and two of the minority centers. Fluorescence lifetimes were determined for several transitions of the dimer center and used to infer energy-transfer rates. Preliminary high-resolution results are reported for the excitation profiles of the two lowest-energy ^{5}$${\mathit{I}}_{8}$${\ensuremath{\rightarrow}}^{5}$${\mathit{F}}_{5} transitions that show complex hyperfine patterns.
Laser-selective excitation and optical-absorption techniques have been used to establish comprehensive sets of energy levels for both the ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$ and hydrogenic varieties of the tetragonal symmetry (C4v{\mathit{C}}_{4\mathit{v}}C4v​) centers in SrF2{\mathrm{SrF}}_{2}SrF2​ and CaF2{\mathrm{CaF}}_{2}CaF2​. Polarization of the various spectral lines was used to determine the symmetry labels of many of the energy levels. Reversals of the ordering of some levels between SrF2{\mathrm{SrF}}_{2}SrF2​ and CaF2{\mathrm{CaF}}_{2}CaF2​ are found and, in particular, the two lowest levels (D1{\mathit{D}}_{1}D1​ and D2{\mathit{D}}_{2}D2​) of the 1^{1}1D2{\mathit{D}}_{2}D2​ multiplet, which are the originating levels for many of the observed emission transitions, have reversed-symmetry label assignments in SrF2{\mathrm{SrF}}_{2}SrF2​ and CaF2{\mathrm{CaF}}_{2}CaF2​. Differences were found between the ground-state Zeeman splittings for the C4v{\mathit{C}}_{4\mathit{v}}C4v​ ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$ and ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ centers for both SrF2{\mathrm{SrF}}_{2}SrF2​ and CaF2{\mathrm{CaF}}_{2}CaF2​. Fluorescence lifetimes of the C4v{\mathit{C}}_{4\mathit{v}}C4v​ hydrogenic centers show a strong dependence on the particular charge-compensating ion present through nonradiative decay processes involving the respective local mode phonons. The upconversion spectra observed for ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$, ${\mathit{T}}^{\mathrm{\ensuremath{-}}}$, and ${\mathit{D}}^{\mathrm{\ensuremath{-}}}$ varieties of the C4v{\mathit{C}}_{4\mathit{v}}C4v​ centers in SrF2{\mathrm{SrF}}_{2}SrF2​ and for the C4v{\mathit{C}}_{4\mathit{v}}C4v​ ${\mathit{F}}^{\mathrm{\ensuremath{-}}}$ center in CaF2{\mathrm{CaF}}_{2}CaF2​ are all consistent with excitation of specific subsets of nearby C4v{\mathit{C}}_{4\mathit{v}}C4v​ centers.
A detailed spectroscopic study of Yb3+:CaF2{\text{Yb}}^{3+}:{\text{CaF}}_{2}Yb3+:CaF2​ is made by using laser selective excitation, low-temperature time-resolved fluorescence, and Raman techniques. Three dominant types of Yb3+{\text{Yb}}^{3+}Yb3+ isolated ion centers are identified at very low (0.03 at. (0.03\text{ }\text{at}\text{.}\text{ }%)(0.03 at.  dopant concentration: two of them with cubic and tetragonal symmetries and the third one not clearly identified but likely of trigonal symmetry. Fluorescence decays strongly differ from one site to another. The overall measured positions of the Stark sublevels of the 2F7/2{^{2}F}_{7/2}2F7/2​ and 2F5/2{^{2}F}_{5/2}2F5/2​ multiplets are satisfactorily explained by the crystal-field calculations. On the other hand, at higher dopant concentrations, only one dominant class of Yb3+{\text{Yb}}^{3+}Yb3+ centers occurs which corresponds to some hexameric cluster in which the Yb3+{\text{Yb}}^{3+}Yb3+ ions site in nearly tetragonal crystal-field environments and whose energy-level positions are discussed and compared with those previously reported in the literature.
When introduced as dopants into Y2O3{\mathrm{Y}}_{2}{\mathrm{O}}_{3}Y2​O3​, Er3+\mathrm{E}{\mathrm{r}}^{3+}Er3+ ions replace Y3+{\mathrm{Y}}^{3+}Y3+ ions at two crystallographic sites of C2{\mathrm{C}}_{2}C2​ and C3i{\mathrm{C}}_{3\mathrm{i}}C3i​ point symmetries. The C3i{\mathrm{C}}_{3\mathrm{i}}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{\mathrm{C}}_{3\mathrm{i}}C3i​ site of Er3+\mathrm{E}{\mathrm{r}}^{3+}Er3+ in Y2O3{\mathrm{Y}}_{2}{\mathrm{O}}_{3}Y2​O3​ for its potential in quantum information science and spectral hole burning applications. Our approach involved absorption and site-selective fluorescence spectroscopy to discern Er3+\mathrm{E}{\mathrm{r}}^{3+}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 ggg tensors for both the ground and excited states, confirming the C3i{\mathrm{C}}_{3\mathrm{i}}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{\mathrm{C}}_{3\mathrm{i}}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.
The observation of two-photon absorption by a very efficient up-converted emission is reported for Ho3+{\mathrm{Ho}}^{3+}Ho3+ in CaF2{\mathrm{F}}_{2}F2​, SrF2{\mathrm{F}}_{2}F2​, and CdF2{\mathrm{F}}_{2}F2​ with both cw- and pulse-laser excitations. The two-photon excitation spectra are found to be highly structured and consist of two bands: The band AAA is excited by the dye-laser photons of frequencies 15 400-15 700 ${\mathrm{cm}}^{\ensuremath{-}1}$: The band BBB is excited by the dye-laser photons of frequencies 15 800-16 400 ${\mathrm{cm}}^{\ensuremath{-}1}$. No one-photon absorption is observed for Ho3+{\mathrm{Ho}}^{3+}Ho3+ in the above lattices at twice these frequencies. Studies of concentration dependence, temperature dependence, and dependence on the pulse repetition rate are used for the assignment of the band. The investigation shows that the two bands AAA and BBB arise from two different modes of two-photon excitation. The band AAA is assigned to arise from a sequential (stepwise) two-photon excitation $^{5}I_{8}\ensuremath{\rightarrow}^{5}F_{5}\ensuremath{\rightarrow}^{5}D_{2}$. The band BBB is assigned to arise from the direct two-photon absorption $^{5}I_{8}\ensuremath{\rightarrow}^{3}L_{8}$. Our results are in agreement with the prediction of the Judd-Ofelt theory of lanthanide transition intensities.
Spectroscopy, Crystal-Field, and Transition Intensity Analyses of the C3v_{\rm 3v}3v​(O2−^{2-}2−) Centre in Er3+^{3+}3+ Doped CaF2_{2}2​ 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 C3v_{\rm 3v}3v​(O2−^{2-}2−) centre in CaF2_22​:Er3+^{3+}3+ as an interesting erbium site case study. The 4^{4}4I15/2_{15/2}15/2​Z1→4_1 \rightarrow {^{4}}1​→4I13/2_{13/2}13/2​Y1_11​ transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the 167^{167}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 4^{4}4I11/2→4_{11/2}\rightarrow {^{4}}11/2​→4I15/2_{15/2}15/2​ and 4^{4}4I13/2→4_{13/2} \rightarrow {^{4}}13/2​→4I15/2_{15/2}15/2​ inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The 4^{4}4I13/2_{13/2}13/2​ excited state lifetime is 25.0\,ms and the intensity calculation is in excellent agreement with this value.
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 4 I 15 / 2 Z 1 → 4 I 13 / 2 Y 1 transition has a low-temperature inhomogeneous linewidth of 1 GHz with hyperfine structure observable from the 167 Er 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 4 I 11 / 2 → 4 I 15 / 2 and 4 I 13 / 2 → 4 I 15 / 2 inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The 4 I 13 / 2 excited state lifetime is 25.0 ms and the intensity calculation is in excellent agreement with this value. • Detailed spectroscopic study of the C 3v (O 2 − ) Centre in CaF 2 :Er 3 + . • Crystal-field fit to 34 energy levels and ground-state magnetic splitting. • Transition intensity analysis for the technologically relevant infrared transitions.