We report a spectroscopic study of the 7F0-5D1 transition of europium ions in crystal yttrium orthosilicate (Eu3+:Y2SiO5) with a focus on low-temperature properties relevant to its use in time-domain optical data storage. The optical dephasing time T2 for this green transition was found to be approximately 50 µs for Eu3+ in one optical site (site 1) and 56 µs for Eu3+ in the other site (site 2), both of which exceeded their respective excited-state lifetimes (32 µs for site 1 and 42 µs for site 2). Of the two optical sites, the transition on site 2 has a slightly larger inhomogeneous linewidth (~2.7 GHz) but a significantly larger oscillator strength (~6 × 10-8), making it a good candidate for time-domain optical storage. The hyperfine structures of the transition for both sites were also measured by spectral hole burning.