Photoluminescence and electroluminescence of the exciplex formed between a terbium ternary complex and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine

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Abstract
We demonstrate the photoluminescence (PL) and electroluminescence (EL) of the exciplex formed between a terbium complex tris-(1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone)-1,10-phenanthroline-terbium Tb(PMIP)3(Phen) and the hole-transporting material N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD). Experimental results show that a new emission peaking at 540 nm from their 1 : 1 mixture and the electroluminescence from the double layer device (ITO/TPD/Tb(PMIP)3(Phen)/Mg0.9Ag0.1) can be assigned to the exciplex formed between the excited state of TPD and the ground state of the terbium complex. By suppressing the formation of the exciplex by changing the carrier combination zone, pure green light from the central terbium ion with highest brightness 250 cd m−2 at 15 V, power efficiency of 0.31 lm W−1 and turn-on voltage as low as 3 V can be obtained from a device of ITO/TPD(10 nm)/Tb(PMIP)3(Phen)(80 nm)/BCP(20 nm)/Mg0.9Ag0.1. By doping TPD into the emitting layer, which facilitates the exciplex formation, bright yellow emission with highest brightness 1180 cd m−2 at 17 V was obtained from a device of ITO/TPD(20 nm)/Tb(PMIP)3(Phen) : TPD(2 : 1)(50 nm)/Tb(PMIP)3(Phen)(20 nm)/AlQ(30 nm)/Mg0.9Ag0.1.