Abstract A number of rare earth chelates show bright line emissions. These emissions usually result from the absorption of energy in the broad absorption band of the chelating agent followed by transfer of this energy to an excited state of the central rare earth metal ion. This transfer is followed by emission from one or more of these excited states. The emission spectrum is characteristic of the rare earth ion -discrete, narrow lines - showing no band characteristic of the chelating agent. To understand the absorption, transfer, and emission of light energy in these materials, the efficiency of energy transfer and the quenching processes involved must be determined. A knowledge of the fluorescence quantum efficiency is essential.