Zeeman Spectroscopy of Vacancy-Charge-Compensated Er3+ Sites in CaWO4 under Vector Magnetic Fields

TL;DR

This study investigates Er3+ ions in CaWO4 using polarization-resolved optical absorption under vector magnetic fields, revealing complex spectral behaviors of vacancy-related sites and providing insights into defect structures relevant for quantum technologies.

Contribution

It identifies and characterizes multiple inequivalent Er3+ sites with reduced symmetry caused by local Ca2+ vacancies, advancing understanding of defect-engineered rare-earth sites.

Findings

Axial Er3+ site shows symmetric Zeeman splitting consistent with S4 symmetry.

Additional sites exhibit complex, interchange of transitions under crystal rotation.

Effective g-factors are extracted and supported by EPR measurements.

Abstract

We present polarization-resolved optical absorption measurements on Er3+ ions in CaWO4 under vector magnetic fields, focusing on charge-compensated sites arising from local Ca2+ vacancies. While the known axial Er3+ site displays a single symmetric Zeeman-split transition pattern consistent with S4 symmetry, two additional sites exhibit more complex spectral behavior, including sets of transitions that interchange under 90{\deg} crystal rotations-evidence of reduced, rhombic-like symmetry. From these polarization- and temperature-dependent spectra, we extract effective g-factors. Our findings are corroborated by electron paramagnetic resonance measurements and support a model of multiple inequivalent Ca2+ vacancies around Er3+ sites in the host lattice. This detailed characterization contributes to understanding defect-engineered rare-earth sites for quantum information applications.