Fluorescence Decay of Rare-Earth Ions in Crystals

The decay of individual fluorescent transitions excited by monochromatic radiation was measured for most rare earths in hexagonal LaCl3 and other lattices. At 4°K the decay was found to be invariably exponential within the experimental errors; at higher temperatures it could occasionally be represented by several exponentials with different lifetimes. The data show that the free interval below the excited level is important for determining the probability for radiationless transitions. For Pr3+ in LaCl3, there is evidence that imprisonment of radiation prolongs noticeably the fluorescence lifetimes.