Lithium tetra-(8-hydroxy-quinolinato) boron for blue electroluminescent applications

We report the optical and electroluminescent properties of the organometallic complex lithium tetra-(8-hydroxy-quinolinato) boron (LiBq(4)). The complex was prepared by the reaction of lithium borohydride with 8-hydroxyquinoline and shows absorption cutoff wavelength of 410 nm and bright blue photoluminescence with a peak wavelength at 466 nm. The ionization potential of LiBq(4) was determined to be similar to 5.6 eV by a photoemission apparatus. Electroluminescence (EL) properties of three-layer light-emitting diodes (LED) of ITO/PVK:TPD/LiBq(4)/Alq(3)/Mg with LiBq(4) as the active layer were characterized. The EL spectra of the three-layer device are similar to the PL spectrum of the single layer LiBq(4) but with peak wavelength at 475 nm. The results indicate that boron complexes are potential blue emitters for LED applications. (C) 1999 American Institute of Physics. [S0003-6951(99)00638-5].