Physical Review B

Spectroscopy and dynamics of Er 3 + : Y 2 Si O 5 at 1.5 μ m

Thomas Böttger, Yazhou Sun, Charles W. Thiel, R. L. Cone

Published Aug 21, 2006• 103 citations

Abstract

We present the results of detailed site-selective spectroscopy performed on the $^{4}I_{15∕2}\ensuremath{\leftrightarrow}^{4}I_{13∕2}$ transition of ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ at $1.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. New determinations of the $^{4}I_{13∕2}$ and $^{4}I_{15∕2}$ crystal-field-level structure for the two crystallographically inequivalent ${\mathrm{Er}}^{3+}$ sites have been made. The fluorescence dynamics of the metastable $^{4}I_{13∕2}:{\mathrm{Y}}_{1}$ excited state was investigated, showing exponential decays for ${\mathrm{Er}}^{3+}$ at both crystallographic sites with fluorescence lifetimes of $11.4\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ for site 1 and $9.2\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ for site 2. Exceptionally sharp inhomogeneous absorption lines of 180, 390, and $510\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ were observed in 0.0015% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$, 0.005% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$, and 0.02% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ crystals, respectively. The $g$-values for the lowest energy $^{4}I_{15∕2}$ $({\mathrm{Z}}_{1})$ and $^{4}I_{13∕2}$ $({\mathrm{Y}}_{1})$ doublets were measured to be 5.5 and 4.6 for site 1 and 15.0 and 12.9 for site 2 when the magnetic field was oriented along the crystal's ${\mathbit{D}}_{1}$ axis.

DOI: 10.1103/physrevb.74.075107

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Optical decoherence, spectroscopy, and magnetic g tensors for the 1.5-µm I 15 / 2 4 − I 13 / 2 4 transitions of E r 3 + dopants at the C 2 -symmetry site in Y 2 O 3

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Demonstration of site-selective angular-resolved absorption spectroscopy of the 4 I 15 ∕ 2 → 4 I 13 ∕ 2 erbium transition in the monoclinic crystal Y 2 SiO 5

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Physical Review B

Spectroscopy and dynamics of Er 3 + : Y 2 Si O 5 at 1.5 μ m

Thomas Böttger, Yazhou Sun, Charles W. Thiel, R. L. Cone

Published Aug 21, 2006• 103 citations

Publisher

Abstract

We present the results of detailed site-selective spectroscopy performed on the

^{4}I_{15∕2}\ensuremath{\leftrightarrow}^{4}I_{13∕2}

transition of

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

1.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}

. New determinations of the

^{4}I_{13∕2}

and

^{4}I_{15∕2}

crystal-field-level structure for the two crystallographically inequivalent

{\mathrm{Er}}^{3+}

sites have been made. The fluorescence dynamics of the metastable

^{4}I_{13∕2}:{\mathrm{Y}}_{1}

excited state was investigated, showing exponential decays for

{\mathrm{Er}}^{3+}

at both crystallographic sites with fluorescence lifetimes of

11.4\phantom{\rule{0.3em}{0ex}}\mathrm{ms}

for site 1 and

9.2\phantom{\rule{0.3em}{0ex}}\mathrm{ms}

for site 2. Exceptionally sharp inhomogeneous absorption lines of 180, 390, and

510\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}

were observed in 0.0015%

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

, 0.005%

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

, and 0.02%

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

crystals, respectively. The

g

-values for the lowest energy

^{4}I_{15∕2}

({\mathrm{Z}}_{1})

and

^{4}I_{13∕2}

({\mathrm{Y}}_{1})

doublets were measured to be 5.5 and 4.6 for site 1 and 15.0 and 12.9 for site 2 when the magnetic field was oriented along the crystal's

{\mathbit{D}}_{1}

axis.

DOI: 10.1103/physrevb.74.075107

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Thomas Böttger, Todd L. Harris, G. D. Reinemer +2 more

Erbium-doped solids are a promising platform for quantum technology due to the $\mathrm{E}{\mathrm{r}}^{3+}$ 1.5-\textmu{}m optical transition in the telecom C band that can offer long coherence times. To characterize the intrinsic ${\mathrm{C}}_{2}$ site of $\mathrm{E}{\mathrm{r}}^{3+}$ in ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ for quantum information and photonic signal-processing applications, absorption and site-selective fluorescence spectroscopy were used to assign the $\mathrm{E}{\mathrm{r}}^{3+}\phantom{\rule{4pt}{0ex}}^{4}I_{15/2}$ $\ensuremath{\leftrightarrow}$ $^{4}I_{13/2}$ transitions. The lowest-to-lowest transition occurs at 1535.608 nm and laser absorption determined an inhomogeneous linewidth of 780 MHz in a 0.005%-doped crystal at 3.4 K. Time-resolved fluorescence established an upper limit for the excited-state lifetime of 8.5 ms. Angular-dependent Zeeman absorption was used to determine ground- and excited-state $g$ tensors. The ${\mathrm{C}}_{2}$ -site $g$ tensor components for the ground state are ${g}_{x}=1.60$ , ${g}_{y}=4.71$ , and ${g}_{z}=11.93$ with a tipping angle of \ensuremath{\alpha} = $2.{06}^{\ensuremath{\circ}}$, whereas for the excited state the components are ${g}_{x}=1.08$ , ${g}_{y}=4.36$ , and ${g}_{z}=10.07$ with a tipping angle of \ensuremath{\alpha} = $\ensuremath{-}11.{7}^{\ensuremath{\circ}}$. Optical decoherence can be suppressed by the application of a magnetic field parallel to $\ensuremath{\langle}111\ensuremath{\rangle}$ crystal axes where all ${\mathrm{C}}_{2}$ sites become nearly magnetically equivalent with large $g$ values so that spin flips of neighboring $\mathrm{E}{\mathrm{r}}^{3+}$ ions can be simultaneously suppressed. Using this magnetic field direction, two-pulse photon echoes gave a homogeneous linewidth of 5 kHz for an applied magnetic field of 0.5 T, narrowing and saturating at 2.5 kHz at 3.5 T. Decoherence over intermediate magnetic fields was described by spectral diffusion due to $\mathrm{E}{\mathrm{r}}^{3+}\text{\ensuremath{-}}\mathrm{E}{\mathrm{r}}^{3+}$ magnetic dipole interactions driven by the direct phonon process. With $\mathrm{E}{\mathrm{r}}^{3+}$ : ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ absorption at a convenient telecom laser wavelength and the ability to fabricate waveguides, our study suggests that this is a promising material system for quantum information and spectral hole-burning signal-processing applications.Erbium-doped solids are a promising platform for quantum technology due to the $\mathrm{E}{\mathrm{r}}^{3+}$ 1.5-\textmu{}m optical transition in the telecom C band that can offer long coherence times. To characterize the intrinsic ${\mathrm{C}}_{2}$ site of $\mathrm{E}{\mathrm{r}}^{3+}$ in ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ for quantum information and photonic signal-processing applications, absorption and site-selective fluorescence spectroscopy were used to assign the $\mathrm{E}{\mathrm{r}}^{3+}\phantom{\rule{4pt}{0ex}}^{4}I_{15/2}$$\ensuremath{\leftrightarrow}$$^{4}I_{13/2}$ transitions. The lowest-to-lowest transition occurs at 1535.608 nm and laser absorption determined an inhomogeneous linewidth of 780 MHz in a 0.005%-doped crystal at 3.4 K. Time-resolved fluorescence established an upper limit for the excited-state lifetime of 8.5 ms. Angular-dependent Zeeman absorption was used to determine ground- and excited-state $g$ tensors. The ${\mathrm{C}}_{2}$-site $g$ tensor components for the ground state are ${g}_{x}=1.60$, ${g}_{y}=4.71$, and ${g}_{z}=11.93$ with a tipping angle of \ensuremath{\alpha} = $2.{06}^{\ensuremath{\circ}}$, whereas for the excited state the components are ${g}_{x}=1.08$, ${g}_{y}=4.36$, and ${g}_{z}=10.07$ with a tipping angle of \ensuremath{\alpha} = $\ensuremath{-}11.{7}^{\ensuremath{\circ}}$. Optical decoherence can be suppressed by the application of a magnetic field parallel to $\ensuremath{\langle}111\ensuremath{\rangle}$ crystal axes where all ${\mathrm{C}}_{2}$ sites become nearly magnetically equivalent with large $g$ values so that spin flips of neighboring $\mathrm{E}{\mathrm{r}}^{3+}$ ions can be simultaneously suppressed. Using this magnetic field direction, two-pulse photon echoes gave a homogeneous linewidth of 5 kHz for an applied magnetic field of 0.5 T, narrowing and saturating at 2.5 kHz at 3.5 T. Decoherence over intermediate magnetic fields was described by spectral diffusion due to $\mathrm{E}{\mathrm{r}}^{3+}\text{\ensuremath{-}}\mathrm{E}{\mathrm{r}}^{3+}$ magnetic dipole interactions driven by the direct phonon process. With $\mathrm{E}{\mathrm{r}}^{3+}$:${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ absorption at a convenient telecom laser wavelength and the ability to fabricate waveguides, our study suggests that this is a promising material system for quantum information and spectral hole-burning signal-processing applications.

Physical review. B./Physical review. BJul 17, 20248 citations

Optical spectroscopy, magnetic g tensors, and decoherence studies of magnetic dipole transitions of E r 3 + at C 3 i -symmetry lattice sites in Y 2 O 3 at 1.5 µm

Thomas Böttger, G. D. Reinemer, Charles W. Thiel +1 more

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

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arXiv:2409.15622Sep 23, 20240 citations

Temperature and concentration dependence of optical dephasing, spectral-hole lifetime, and anisotropic absorption in Eu 3 + : Y 2 SiO 5

Flurin Könz, Y. Sun, Charles W. Thiel +4 more

Detailed site-selective spectroscopy has been performed as a function of temperature on the ${}^{7}{F}_{0}{\ensuremath{\leftrightarrow}}^{5}{D}_{0}$ transition of ${\mathrm{Eu}}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ for ${\mathrm{Eu}}^{3+}$ concentrations of 0.02%, 0.1%, 0.5%, and 1%. Time-domain optical dephasing, spectral hole lifetimes, anisotropic absorption coefficients, inhomogeneous linewidths, and fluorescence lifetimes for ${\mathrm{Eu}}^{3+}$ ions at both crystallographic sites were measured. The temperature dependence of the optical dephasing, transition energy, and linewidth of the ${}^{7}{\stackrel{\ensuremath{\rightarrow}}{{F}_{0}}}^{5}{D}_{0}$ absorption was measured and interpreted in terms of Raman scattering of phonons. Photon echo measurements of optical dephasing gave ${T}_{2}$ values as long as 2.6 ms, approaching the limit set by the fluorescence decay time. Spectral hole lifetimes were measured for temperatures from 2 K to 18 K, with observed lifetimes varying from 1 s at 18 K to an estimated value of greater than 20 days at 2 K. Anisotropic absorption coefficients were measured, and an increase in ${\mathrm{Eu}}^{3+}$ concentration from 0.02% to 7% produced an increase in the inhomogeneous linewidth ${\ensuremath{\Gamma}}_{\mathrm{inh}}$ from 0.5 GHz to \ensuremath{\sim}150 GHz, indicating that ${\mathrm{Eu}}^{3+}$ doping induces significant strain in the crystal. New determinations of many energy levels of ${}^{7}{F}_{J}$ multiplets have been made for $J=0$ to 6.Detailed site-selective spectroscopy has been performed as a function of temperature on the ${}^{7}{F}_{0}{\ensuremath{\leftrightarrow}}^{5}{D}_{0}$ transition of ${\mathrm{Eu}}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ for ${\mathrm{Eu}}^{3+}$ concentrations of 0.02%, 0.1%, 0.5%, and 1%. Time-domain optical dephasing, spectral hole lifetimes, anisotropic absorption coefficients, inhomogeneous linewidths, and fluorescence lifetimes for ${\mathrm{Eu}}^{3+}$ ions at both crystallographic sites were measured. The temperature dependence of the optical dephasing, transition energy, and linewidth of the ${}^{7}{\stackrel{\ensuremath{\rightarrow}}{{F}_{0}}}^{5}{D}_{0}$ absorption was measured and interpreted in terms of Raman scattering of phonons. Photon echo measurements of optical dephasing gave ${T}_{2}$ values as long as 2.6 ms, approaching the limit set by the fluorescence decay time. Spectral hole lifetimes were measured for temperatures from 2 K to 18 K, with observed lifetimes varying from 1 s at 18 K to an estimated value of greater than 20 days at 2 K. Anisotropic absorption coefficients were measured, and an increase in ${\mathrm{Eu}}^{3+}$ concentration from 0.02% to 7% produced an increase in the inhomogeneous linewidth ${\ensuremath{\Gamma}}_{\mathrm{inh}}$ from 0.5 GHz to \ensuremath{\sim}150 GHz, indicating that ${\mathrm{Eu}}^{3+}$ doping induces significant strain in the crystal. New determinations of many energy levels of ${}^{7}{F}_{J}$ multiplets have been made for $J=0$ to 6.

Physical review. B, Condensed matterAug 25, 2003195 citations

Demonstration of site-selective angular-resolved absorption spectroscopy of the 4 I 15 ∕ 2 → 4 I 13 ∕ 2 erbium transition in the monoclinic crystal Y 2 SiO 5

Yannick G. Petit, Benoı̂t Boulanger, Jérôme Debray +1 more

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arXiv:2005.13626Optical Materials XAug 8, 20207 citations

Hyperfine interaction of Er 3 + ions in Y 2 Si O 5 : An electron paramagnetic resonance spectroscopy study

O. Guillot-Noël, Philippe Goldner, Y. Le Du +3 more

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 $[^{4}I_{15∕2}(0)]$ of ${\mathrm{Er}}^{3+}$ ions in ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ . 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.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 $[^{4}I_{15∕2}(0)]$ of ${\mathrm{Er}}^{3+}$ ions in ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$. 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.

Physical Review BDec 11, 200681 citations

We present the results of detailed site-selective spectroscopy performed on the

^{4}I_{15∕2}\ensuremath{\leftrightarrow}^{4}I_{13∕2}

transition of

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

1.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}

. New determinations of the

^{4}I_{13∕2}

and

^{4}I_{15∕2}

crystal-field-level structure for the two crystallographically inequivalent

{\mathrm{Er}}^{3+}

sites have been made. The fluorescence dynamics of the metastable

^{4}I_{13∕2}:{\mathrm{Y}}_{1}

excited state was investigated, showing exponential decays for

{\mathrm{Er}}^{3+}

at both crystallographic sites with fluorescence lifetimes of

11.4\phantom{\rule{0.3em}{0ex}}\mathrm{ms}

for site 1 and

9.2\phantom{\rule{0.3em}{0ex}}\mathrm{ms}

for site 2. Exceptionally sharp inhomogeneous absorption lines of 180, 390, and

510\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}

were observed in 0.0015%

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

, 0.005%

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

, and 0.02%

{\mathrm{Er}}^{3+}:{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

crystals, respectively. The

g

-values for the lowest energy

^{4}I_{15∕2}

({\mathrm{Z}}_{1})

and

^{4}I_{13∕2}

({\mathrm{Y}}_{1})

doublets were measured to be 5.5 and 4.6 for site 1 and 15.0 and 12.9 for site 2 when the magnetic field was oriented along the crystal's

{\mathbit{D}}_{1}

axis.

Erbium-doped solids are a promising platform for quantum technology due to the

\mathrm{E}{\mathrm{r}}^{3+}

1.5-\textmu{}m optical transition in the telecom C band that can offer long coherence times. To characterize the intrinsic

{\mathrm{C}}_{2}

site of

\mathrm{E}{\mathrm{r}}^{3+}

{\mathrm{Y}}_{2}{\mathrm{O}}_{3}

for quantum information and photonic signal-processing applications, absorption and site-selective fluorescence spectroscopy were used to assign the

\mathrm{E}{\mathrm{r}}^{3+}\phantom{\rule{4pt}{0ex}}^{4}I_{15/2}

$\ensuremath{\leftrightarrow}$

^{4}I_{13/2}

transitions. The lowest-to-lowest transition occurs at 1535.608 nm and laser absorption determined an inhomogeneous linewidth of 780 MHz in a 0.005%-doped crystal at 3.4 K. Time-resolved fluorescence established an upper limit for the excited-state lifetime of 8.5 ms. Angular-dependent Zeeman absorption was used to determine ground- and excited-state

g

tensors. The

{\mathrm{C}}_{2}

-site

g

tensor components for the ground state are

{g}_{x}=1.60

{g}_{y}=4.71

, and

{g}_{z}=11.93

with a tipping angle of \ensuremath{\alpha} = $2.{06}^{\ensuremath{\circ}}$, whereas for the excited state the components are

{g}_{x}=1.08

{g}_{y}=4.36

, and

{g}_{z}=10.07

with a tipping angle of \ensuremath{\alpha} = $\ensuremath{-}11.{7}^{\ensuremath{\circ}}$. Optical decoherence can be suppressed by the application of a magnetic field parallel to $\ensuremath{\langle}111\ensuremath{\rangle}$ crystal axes where all

{\mathrm{C}}_{2}

sites become nearly magnetically equivalent with large

g

values so that spin flips of neighboring

\mathrm{E}{\mathrm{r}}^{3+}

ions can be simultaneously suppressed. Using this magnetic field direction, two-pulse photon echoes gave a homogeneous linewidth of 5 kHz for an applied magnetic field of 0.5 T, narrowing and saturating at 2.5 kHz at 3.5 T. Decoherence over intermediate magnetic fields was described by spectral diffusion due to $\mathrm{E}{\mathrm{r}}^{3+}\text{\ensuremath{-}}\mathrm{E}{\mathrm{r}}^{3+}$ magnetic dipole interactions driven by the direct phonon process. With

\mathrm{E}{\mathrm{r}}^{3+}

{\mathrm{Y}}_{2}{\mathrm{O}}_{3}

absorption at a convenient telecom laser wavelength and the ability to fabricate waveguides, our study suggests that this is a promising material system for quantum information and spectral hole-burning signal-processing applications.

When introduced as dopants into

{\mathrm{Y}}_{2}{\mathrm{O}}_{3}

\mathrm{E}{\mathrm{r}}^{3+}

ions replace

{\mathrm{Y}}^{3+}

ions at two crystallographic sites of

{\mathrm{C}}_{2}

and

{\mathrm{C}}_{3\mathrm{i}}

point symmetries. The

{\mathrm{C}}_{3\mathrm{i}}

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

{\mathrm{C}}_{3\mathrm{i}}

site of

\mathrm{E}{\mathrm{r}}^{3+}

{\mathrm{Y}}_{2}{\mathrm{O}}_{3}

for its potential in quantum information science and spectral hole burning applications. Our approach involved absorption and site-selective fluorescence spectroscopy to discern

\mathrm{E}{\mathrm{r}}^{3+}

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

{\mathrm{C}}_{3\mathrm{i}}

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

{\mathrm{C}}_{3\mathrm{i}}

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.

Spectroscopy, Crystal-Field, and Transition Intensity Analyses of the C

_{\rm 3v}

^{2-}

) Centre in Er

^{3+}

Doped CaF

_{2}

Crystals

_{\rm 3v}

^{2-}

) centre in CaF

_2

:Er

^{3+}

as an interesting erbium site case study. The

^{4}

_{15/2}

_1 \rightarrow {^{4}}

_{13/2}

_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}

_{11/2}\rightarrow {^{4}}

_{15/2}

and

^{4}

_{13/2} \rightarrow {^{4}}

_{15/2}

inter-multiplet transitions are in excellent agreement with the experimentally measured spectra. The

^{4}

_{13/2}

excited state lifetime is 25.0\,ms and the intensity calculation is in excellent agreement with this value.

Detailed site-selective spectroscopy has been performed as a function of temperature on the ${}^{7}{F}_{0}{\ensuremath{\leftrightarrow}}^{5}{D}_{0}$ transition of

{\mathrm{Eu}}^{3+}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}

for

{\mathrm{Eu}}^{3+}

concentrations of 0.02%, 0.1%, 0.5%, and 1%. Time-domain optical dephasing, spectral hole lifetimes, anisotropic absorption coefficients, inhomogeneous linewidths, and fluorescence lifetimes for

{\mathrm{Eu}}^{3+}

ions at both crystallographic sites were measured. The temperature dependence of the optical dephasing, transition energy, and linewidth of the ${}^{7}{\stackrel{\ensuremath{\rightarrow}}{{F}_{0}}}^{5}{D}_{0}$ absorption was measured and interpreted in terms of Raman scattering of phonons. Photon echo measurements of optical dephasing gave

{T}_{2}

values as long as 2.6 ms, approaching the limit set by the fluorescence decay time. Spectral hole lifetimes were measured for temperatures from 2 K to 18 K, with observed lifetimes varying from 1 s at 18 K to an estimated value of greater than 20 days at 2 K. Anisotropic absorption coefficients were measured, and an increase in

{\mathrm{Eu}}^{3+}

concentration from 0.02% to 7% produced an increase in the inhomogeneous linewidth ${\ensuremath{\Gamma}}_{\mathrm{inh}}$ from 0.5 GHz to \ensuremath{\sim}150 GHz, indicating that

{\mathrm{Eu}}^{3+}

doping induces significant strain in the crystal. New determinations of many energy levels of

{}^{7}{F}_{J}

multiplets have been made for

J=0

to 6.

[^{4}I_{15∕2}(0)]

{\mathrm{Er}}^{3+}

ions in

{\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}

. 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.