Spectrally-resolved hyperfine interactions between polaron and nuclear   spins in organic light emitting diodes: Magneto-EL studies
  We use spectrally-resolved magneto-electroluminescence (EL) measurements to study the energy dependence of hyperfine interactions between polaron and nuclear spins in organic LEDs. Using layered devices based on Bphen/MTDATA -- a well-known exciplex emitter -- we show that the increase in EL emission intensity $I$ due to small applied magnetic fields of order 100 mT is markedly larger at the high-energy blue end of the EL spectrum (dI/I ~11%) than at the low-energy red end (~4%). Concurrently, the widths of the magneto-EL curves increase monotonically from blue to red, revealing an increasing hyperfine coupling between polarons and nuclei and directly providing insight into the energy-dependent spatial extent and localization of polarons. 
S. A. Crooker, F. Liu, M. R. Kelley, N. J. D. Martinez, W. Nie, A.   Mohite, I. H. Nayyar, S. Tretiak, D. L. Smith, and P. P...
cond-mat.mtrl-sci