Theory of Internal Conversion of the ^{229}Th Nuclear Isomer in Solid-State Hosts

Laser excitation of ^{229}Th nuclei in doped wide band gap crystals has been demonstrated recently, opening the possibility of developing ultrastable solid-state clocks and sensitive searches for new physics. We develop a quantitative theory of the internal conversion (IC) of isomeric ^{229}Th in solid-state hosts and elucidate a crucial requirement in choosing the solid-state hosts in nuclear clock applications. The IC of the isomer proceeds by resonantly exciting a valence band electron to a defect state, accompanied by multiphonon emission. We demonstrate that, if the process is energetically allowed, it generally quenches the isomer on a millisecond timescales, much faster than the isomer's radiative lifetime, despite ^{229}Th being in the +4 charge state in the valence band.