Near-infrared-emitting rare-earth chelates based on 8-hydroxyquinoline have appeared frequently in recent literature, because they are promising candidates for active components in near-infrared-luminescent optical devices, such as optical amplifiers, organic light-emitting diodes, .... Unfortunately, the absence of a full structural investigation of these rare-earth quinolinates is hampering the further development of rare-earth quinolinate based materials, because the luminescence output cannot be related to the structural properties. After an elaborate structural elucidation of the rare-earth quinolinate chemistry we can conclude that basically three types of structures can be formed, depending on the reaction conditions: tris complexes, corresponding to a 1:3 metal-to-ligand ratio, tetrakis complexes, corresponding to a 1:4 metal-to-ligand ratio, and trimeric complexes, with a 3:8 metal-to-ligand ratio. The intensity of the emitted near-infrared luminescence of the erbium(III) complexes is highest for the tetrakis complexes of the dihalogenated 8-hydroxyquinolinates.
Substitution of the hydrogen atoms in the 5-and 7-positions of the quinoline moiety by halogen atoms (Cl and Br) increases the near-infrared (NIR) photoluminescence intensity of the trivalent erbium ion by 30%.
Narrow bandwidth red electroluminescence from OLED devices fabricated using a simple solution-based approach is demonstrated. A spin-casting method is employed to fabricate organic light emitting diode (OLED) devices comprising a poly(N-vinylcarbazole) (PVK) host matrix doped with a europium h-diketonate complex, Eu(dbm) 3 (Phen) (dibenzoylmethanate, dbm; 1,10-phenanthroline, Phen) on glass/ indium tin oxide (ITO)/3,4-polyethylene-dioxythiophene-polystyrene sulfonate (PEDOT) substrates. Saturated red europium ion emission, based on the 5 D 0 Y 7 F 2 transition, is centered at a wavelength of 612 nm with a full width at half maximum of 3.5 nm. A maximum external quantum efficiency of 6.3 Â 10 À 2 cd/A (3.1 Â10 À 2 %) and a maximum luminance of 130 cd/m 2 at 400 mA/cm 2 and 25 V is measured for ITO/PEDOT/PVK:Eu(dbm) 3 (Phen)/Ca/Al devices. This measured output luminance is comparable to that of devices fabricated using more sophisticated small molecule evaporation techniques.
A structurally pure, near-infrared emissive Nd-(5,7-dichloro-8-hydroxyquinoline) 4 tetrakis complex has been synthesized. When incorporated as a dopant in the blue emissive, hole conducting polymer poly(N-vinylcarbazole), PVK, sensitized neodymium ion emission was observed following photo-excitation of the polymer host. OLED devices were fabricated by spin-casting layers of the doped polymer onto glass/indium tin oxide (ITO)/3,4-polyethylene-dioxythiophene-polystyrene sulfonate (PEDOT) substrates. An external quantum efficiency of 1 × 10 − 3 % and a near-infrared irradiance of 2.0 nW/mm 2 at 25 mA/mm 2 and 20 V was achieved using glass/ITO/PEDOT/ PVK:Nd-(5,7-dichloro-8hydroxyquinoline) 4 /Ca/Al devices.
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