Demonstration of site-selective angular-resolved absorption spectroscopy of the $^{4}I_{15/2} \rightarrow $$^{4}I_{13/2}$ erbium transition in the monoclinic crystal Y$_2$SiO$_5$

TL;DR

This study demonstrates a site-selective, angular-resolved absorption spectroscopy technique for the erbium transition in Y$_2$SiO$_5$, revealing anisotropic properties and hybrid electric-magnetic transition nature at low temperatures.

Contribution

It introduces a novel site-selective angular-resolved spectroscopy method to analyze the anisotropy and transition nature of erbium in Y$_2$SiO$_5$ at low temperatures.

Findings

Revealed anisotropic absorption properties in Y$_2$SiO$_5$

Identified the hybrid electric-magnetic nature of the erbium transition

Spectrally resolved and characterized two yttrium sites

Abstract

We study the angular dependence in polarized light of the optical absorption for the Er$^{3+}$ transition $^{4}I_{15/2} \rightarrow $$^{4}I_{13/2}$ in Y$_2$SiO$_5$, revealing thus the associated anisotropy and the orientation of the related absorption principal directions in the dielectric plan perpendicular to the monoclinic axis b. The measurements are performed at low temperature. This allows us to isolate the lowest crystal field levels in the ground and excited states. We spectrally resolve and independently characterize the two yttrium substitution sites in the Y$_2$SiO$_5$ matrix. The absorption tensor components cannot be unambiguously determined yet while only considering the investigated dielectric plane. Still, measurements remarkably demonstrate that this transition of interest well resolved at low temperature is not only a magnetic-dipole allowed transition but indeed a hybrid electric-magnetic transition.