Ultrathin Eu- and Er-Doped Y2O3 Films with Optimized Optical Properties for Quantum Technologies

Atomic layer deposited (ALD) Y2O3 thin films have been thoroughly
investigated for optical or electronic applications. The coherent spectroscopy of
lanthanide ions doped into this material has also recently attracted increasing interest
in the field of quantum technologies for which they are considered promising candidates
in quantum memories or as spin−photon interfaces. However, these most demanding
applications require a deep control over the local positioning of the ions and their close
environment in the crystalline matrix. This study focuses on the structural as well as
optical properties of Eu3+ and Er3+ dopants in Y2O3 using photoluminescence (PL),
luminescence decay times, and inhomogeneous line width (Γinh) measurements within
this particular context. While as-grown ALD films do not provide an ideal host for the
emitters, we demonstrate that by optimizing the deposition conditions and using
appropriate annealing post treatments narrow inhomogeneous lines can be obtained for
the 7F0 ↔ 5D0 transition of Eu3+ even for nanoscale films. Furthermore, about 1.5 ms
lifetime has been measured for the infrared telecom transition of Er in ultrathin films (<10 nm), which is an order of magnitude higher than in nanoparticles of the same size. These results validate optimized rare-earth-doped ALD Y2O3 films as a suitable platform for photonics applications where few-nanometer-thick films with well-localized emitters are mandatory. This approach provides the first building blocks toward the development of more complex devices for quantum sensing or hybrid structures coupled with other systems such as two-dimensional materials.