Luminescence of Exchange Coupled Pairs of Transition Metal Ions

The influence of exchange interaction between paramagnetic ions on the luminescence properties is investigated for and pairs. Two effects are reported: shortening of the lifetime of the spin-forbidden emission and a shift of emission lines or bands to a longer wavelength. The shortening of the lifetime of the spin-forbidden emission is important in doped phosphors. For application of -doped phosphors in displays the long lifetime of the emission is a problem. Shortening of the lifetime is possible by exchange coupling with neighbors, or possibly other paramagnetic neighbors. The results reported here show that the lifetime shortening depends on the exchange-coupling parameter J. The strongest coupling is observed in pairs and the lifetime shortening is strong (e.g., in and the lifetime is about 30 times shorter for the pair emission). The coupling in and pairs is weak. Typically, values for J are around 1 cm−1 and the lifetime is reduced by a factor of 2-10 (e.g., J is −1.0 cm−1 for exchange coupling between and the lifetime of the spin-forbidden emission is 14 ms in compared to 56 ms in The lifetime shortening for the emission is not related to the observed red shift for the pair emission. For the pair the exchange interaction is very weak and no significant lifetime shortening could be measured for pairs (24 ms for the emission in vs. 22 ms in © 2001 The Electrochemical Society. All rights reserved.