The influence of exchange interaction between paramagnetic ions on the luminescence properties is investigated for Mn 2ϩ-Mn 2ϩ , Cr 3ϩ-Cr 3ϩ , Cr 3ϩ-Gd 3ϩ , and Mn 2ϩ-Gd 3ϩ 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 Mn 2ϩ doped phosphors. For application of Mn 2ϩ-doped phosphors in displays the long lifetime of the Mn 2ϩ emission is a problem. Shortening of the lifetime is possible by exchange coupling with Mn 2ϩ 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 Cr 3ϩ-Cr 3ϩ pairs and the lifetime shortening is strong ͑e.g., in LaAlO 3 :Cr 3ϩ J ϭ 63 cm Ϫ1 and the lifetime is about 30 times shorter for the pair emission͒. The coupling in Mn 2ϩ-Mn 2ϩ and Cr 3ϩ-Gd 3ϩ pairs is weak. Typically, values for J are around 1 cm Ϫ1 and the lifetime is reduced by a factor of 2-10 ͑e.g., J is Ϫ1.0 cm Ϫ1 for exchange coupling between Cr 3ϩ and Gd 3ϩ ; the lifetime of the spin-forbidden Cr 3ϩ emission is 14 ms in GdAlO 3 compared to 56 ms in LaAlO 3 ͒. The lifetime shortening for the Mn 2ϩ emission is not related to the observed red shift for the pair emission. For the Mn 2ϩ-Gd 3ϩ pair the exchange interaction is very weak and no significant lifetime shortening could be measured for Gd 3ϩ-Mn 2ϩ pairs ͑24 ms for the Mn 2ϩ emission in YF 3 vs. 22 ms in GdF 3 ͒.

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