Picosecond lifetimes and infrared spectroscopy of hydrogenic sites in KY3F10 and LiYF4

A single H− site with axial symmetry is observed for LiYF4 crystals while two distinct H− sites of axial and rhombic symmetry are observed for KY3F10 crystals. Infrared pump–probe measurements yield 10 K lifetimes of 2.7 and 14 ps for the axial H− sites in LiYF4 and KY3F10, respectively. The temperature dependence of relaxation processes for these H− modes is modelled on a combination of anharmonic phonon decay and elastic-phonon scattering processes.