Quenching of Pr3+1S0 emission by Eu3+ and Yb3+

Energy transfer between Pr3+ and Eu3+ is studied by luminescence spectroscopy and time-resolved measurements. In earlier experiments, Zachau et al. (Proceedings-Electrochemical Society, 97 (29) (Luminescent Materials, pp. 314-324, 1998)) observed no energy transfer from the 1S0 level of Pr3+ to the 5D3 level of Eu3+ for YF3:Pr, Eu, in spite of the favorable spectral overlap for energy transfer. This unexpected result was not explained. To resolve this issue, we first calculate the critical distance for energy transfer using the Förster theory and show that efficient energy transfer between Pr3+ and nearest Eu3+ neighbors is predicted. Nevertheless, luminescence experiments show no Eu3+ emission upon excitation in the 1S0 level of Pr3+ in YF3:Pr, Eu confirming the results in (Proceedings-Electrochemical Society, 97 (29) (Luminescent Materials, pp. 314-324, 1998)). The experiments do show a strong quenching of the 1S0 emission by Eu3+. The quenching is explained by a low-energy metal-to-metal charge transfer state (Pr4+-Eu2+) for Pr-Eu pairs. Additional support for this quenching mechanism is provided by the observation that addition of Yb3+ also quenches the 1S0 emission.