ENERGY-TRANSFER FROM GD3+ TO ER3+ IN Y0.34GD0.65ER0.01F3

The energy transfer from the P-6(7/2), level of Gd3+ to the P-2(3/2) l evel of Er3+ is studied in the phosphor Y0.34Gd0.65Er0.01F3. The lifet ime of the P-6(7/2) level of Gd3+ decreases substantially in the prese nce of Er, indicating that the transfer is nonradiative. The transfer is studied in the temperature range from 20 to 300 K, and is found to be more efficient at low temperatures. A model is proposed to explain this behavior, in which we consider the distribution of the ions in th e Stark levels involved in the transfer, and the presence of one- and two-phonon processes.