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 $({\mathrm{LiBq}}_{\mathrm{4}}\mathrm{).}$ 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 ${\mathrm{LiBq}}_{\mathrm{4}}$ was determined to be ∼5.6 eV by a photoemission apparatus. Electroluminescence (EL) properties of three-layer light-emitting diodes (LED) of ${\mathrm{ITO/PVK:TPD/LiBq}}_{\mathrm{4}}{\mathrm{/Alq}}_{\mathrm{3}}\mathrm{/Mg}$ with ${\mathrm{LiBq}}_{\mathrm{4}}$ as the active layer were characterized. The EL spectra of the three-layer device are similar to the PL spectrum of the single layer ${\mathrm{LiBq}}_{\mathrm{4}}$ but with peak wavelength at 475 nm. The results indicate that boron complexes are potential blue emitters for LED applications.