Electron-phonon relaxation in5D4 of Tb3+ in yttrium aluminium garnet

Abstract

The electron-phonon relaxation times of the crystal-field levels of the metastable state5D4 of Tb3+ were measured between 2 and 4.2K. The relaxation of the lowest pseudodoublet (ΔE=1.25 cm−1) shows an Orbach process via higher crystal-field levels. The other levels show direct relaxation on a nanosecond time scale. The higher crystal-field levels were used to look for propagation of high-energy (ν≦4THz) nonequilibrium phonons by phonon-induced fluorescence. No ballistic propagation of high-energy phonons could be found.