Rare-earth minerals are a class of materials with similar properties that are currently used to build a variety of devices, including LEDs, rechargeable batteries, magnets, lasers, and much more. These materials’ electron spins can be hosted in crystals, creating systems with unique characteristics that could serve as interfaces between telecom-band photons and long-lived spin quantum bits.
Source:
https://phys.org/news/2020-05-individual-nuclear-rare-earth-ions-hosted.html