Energy transfer probability in organic electrophosphorescence device with dopant |
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Authors: | Dai Guo-Zhang Li Hong-Jian Pan Yan-Zhi Dai Xiao-Yu and Xie Qiang |
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Institution: | Department of Applied Physics, Hunan University, Changsha 410082, China |
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Abstract: | Based on the energy transfer process from host to dopant in an organic
electrophosphorescent (EP) device, the expression of energy transfer
probability ($\eta )$ between the host (TPD) and guest (Ir(ppy)$_{3})$ EP
systems was proposed. The results show that: ({1}) The rate of the triplet
energy transfer ($K_{\rm HG}$ and $K_{\rm GH})$ increases exponentially with
increasing donor-acceptor molecular distance ($R$), whereas decreases as the
intermolecular distance ($R_{\rm HH})$ increases from 0.8 to 2.4 nm.
Furthermore, $K_{\rm GH}$ changes more quickly than $K_{\rm HG.}$ ({2}) The energy
transfer probability ($\eta )$ increases as $R$ reduces, and the $R_{\rm HH}$
changes can be safely neglected for $R<$0.9 nm. The situation changes for
0.9nm$ < R < 1.1$nm, $R_{\rm HH }$ ($<1$nm) plays an essential role when
$\eta $ changes
and increases with the latter. However, if $R > 1.1$nm, the transfer
probability will be below zero. Here, the energy transfer principle may be
less important, and the high electroluminescence (EL) quantum efficiency of
phosphorescent system will be attributed to the direct electron-hole
recombination in phosphorescent molecules. ({3}) The $\eta $ will increase when the
Forster radius ($R_{0})$ increases or Gibb's energy decreases. |
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Keywords: | electrophosphorescence energy transfer triplet |
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