Nonradiative decay from 5d states of rare earths in crystals

Nonradiative decay from 4f^n?1 5d states was investigated for trivalent rare earths in Y₃Al₅O₁₂. The rates of both 5d→4f and 5d→5d transitions were determined from measurements of the lifetimes and intensities of 5d fluorescence from Ce³⁺ and Pr³⁺. Because of the stronger ion-lattice coupling, nonradiative decay rates for transitions involving 5d states are much faster than those between 4f states. Decay rates are dependent upon the temperature and the energy gap to the next-lower level. The temperature dependences of the 5d fluorescence lifetimes from 77 to 700°K are reported.