Spectroscopy and dynamics of ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ at $1.5\mu \mathrm{m}$

We present the results of detailed site-selective spectroscopy performed on the ${}^{4}I_{15∕2}\leftrightarrow {}^{4}I_{13∕2}$ transition of ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ at $1.5\mu \mathrm{m}$. 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 $11.4\mathrm{ms}$ for site 1 and $9.2\mathrm{ms}$ for site 2. Exceptionally sharp inhomogeneous absorption lines of 180, 390, and $510\mathrm{MHz}$ 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 ${}^{4}I_{15∕2}$ $\left({\mathrm{Z}}_1\right)$ and ${}^{4}I_{13∕2}$ $\left({\mathrm{Y}}_1\right)$ 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 ${\mathit{D}}_1$ axis.

Figure 1

Absorption spectrum polarized $\mathbf{E}\Vert {\mathbf{D}}_2$ for 2% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ at $T=1.95\mathrm{K}$. Water-absorption lines and interference fringes have been removed for better visibility. Absorption-line center energies are given in wave numbers $\left({\mathrm{cm}}^{-1}\right)$, and the numbers in parentheses show the crystallographic site assignments from site-selective fluorescence experiments. Laser site-selective excitation was not available above $6700{\mathrm{cm}}^{-1}$, so several ${}^{4}I_{13∕2}$ levels were not assigned to specific sites.

Figure 2

Site-selective fluorescence spectra for 0.0015% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ at $T=10\mathrm{K}$; line-center energies are given in wave numbers $\left({\mathrm{cm}}^{-1}\right)$. (a) Laser excitation of site 1 ${}^{4}I_{15∕2}\left({\mathrm{Z}}_1\right)\to {}^{4}I_{13∕2}\left({\mathrm{Y}}_2\right)$. (b) Laser excitation of site 2 ${}^{4}I_{15∕2}\left({\mathrm{Z}}_1\right)\to {}^{4}I_{13∕2}\left({\mathrm{Y}}_2\right)$.

Figure 3

Crystal-field energy levels of ${}^{4}I_{15∕2}$ and ${}^{4}I_{13∕2}$ multiplets in wave numbers for ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ determined from absorption and site-selective fluorescence excitation for site 1 and site 2.

Figure 4

Fluorescence decay for 0.0015% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ ${}^{4}I_{13∕2}\left({\mathrm{Y}}_1\right)\to {}^{4}I_{15∕2}\left({\mathrm{Z}}_1\right)$ transition at $T=10\mathrm{K}$; (a) site 1, (b) site 2. Straight lines correspond to exponential least-square fits to the data. The rise time is indicative of the excitation pulse duration.

Figure 5

Laser-absorption spectra polarized $\mathbf{E}\Vert {\mathbf{D}}_2$ and $\mathbf{k}\Vert \mathbf{b}$ for 0.0015%, 0.005%, and 0.02% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ at $T=5\mathrm{K}$.

Figure 6

Polarized laser-absorption spectra $\mathbf{k}\Vert \mathbf{b}$ for 0.005% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ at $T=5\mathrm{K}$.

Figure 7

Transition labeling scheme for the ${}^{4}I_{15∕2}\left({\mathrm{Z}}_1\right)\to {}^{4}I_{13∕2}\left({\mathrm{Y}}_1\right)$ transition in a magnetic field.

Figure 8

Laser-absorption Zeeman spectra for 0.0015% ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2\mathrm{Si}{\mathrm{O}}_5$ as a function of magnetic field for $\mathbf{B}\Vert {\mathbf{D}}_1$ measured with $\mathbf{k}\Vert \mathbf{b}$ at $T=5\mathrm{K}$. (a) Sample laser-absorption scans for site 1 as the magnetic field is varied; subplots have been shifted vertically for better visibility. (b) Zeeman transitions for site 1 and (c) Zeeman transitions for site 2 as a function of magnetic field between $B=0$ and $B=2.6\mathrm{T}$; straight lines are fitted transition energies using Eqs. (3, 4).