Luminescence of Exchange Coupled Pairs of Transition Metal Ions

By A. Vink, M. Bruin, S. Roke, P. S. Peijzel, A. Meijerink. 2001

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The influence of exchange interaction between paramagnetic ions on the luminescence properties is investigated for Mn 2+ -Mn 2+ . Cr 3+ -Cr 3+ , Cr 3+ -Gd 3+ , and Mn 2+ -Gd 3+ pairs. Two effects are reported: shortening of the lifetime of the spin-forbidden emission and a shift of emission lines or hands to a longer wavelength. The shortening of the lifetime of the spin-forbidden emission is important in Mn 2+ doped phosphors. For application of Mn 2+ -doped phosphors in displays the long lifetime of the Mn 2+ emission is a problem. Shortening of the lifetime is possible by exchange coupling with Mn 2+ 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 3+ -Cr 3+ pairs and the lifetime shortening is strong (e.g., in LaAlO 3 :Cr 3+ J = 63 cm 1 and the lifetime is about 30 times shorter for the pair emission). The coupling in Mn 2+ -Mn 2+ and Cr 3+ -Gd 3+ pairs is weak. Typically, values for J are around I 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 Cr 3+ and Gd 3+ ; the lifetime of the spin-forhidden Cr 3+ emission is 14 ms in GdAlO 3 compared to 56 ms in LaAlO 3 ). The lifetime shortening for the Mn 2+ emission is not related to the observed red shift for the pair emission. For the Mn 2+ -Gd 3+ pair the exchange interaction is very weak and no significant lifetime shortening could he measured for Gd 3+ -Mn 2+ pairs (24 ms for the Mn 2+ emission in YF 3 vs. 22 ms in GdF 3 ).

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/a370012dd458fe4ae32414e13d6952d8711c3e98