Materials for optical memory: Resolved hyperfine structure in KY3F10:Ho3+

• Requirements for materials to be used in quantum optical memories are reviewed.
• Resolved hyperfine structure is observed in optical and EPR spectra of KYF:Ho3+.
• Hyperfine structure is modeled on the basis of crystal-field calculations.
• Ground-state structure of KYF:Ho3+ is favorable for QOM applications.

Basic principles of creating a quantum optical memory (QOM) and requirements for relevant materials, in particular, for crystals doped with rare-earth ions, are briefly reviewed. A combined approach to studying the hyperfine structure, which is essential for QOM applications, is presented on the example of KY3F10:Ho3+.