Effect of Different Alkyl Groups at the N-Position on the Luminescence of Carbazole-Based β-Diketonate Europium(III) Complexes

A series of carbazole-based beta-diketone derivatives and their europium(III) ternary complexes Eu(N-Cx)(3)phen were designed and synthesized, where N-Cx denotes carbazole-based beta-diketonates with different alkyl substituents at N-position of the carbazole ring and phen is 1,10-phenethroline. Thermogravimetric analysis (TGA) shows that the decomposition temperature of the complexes is over 360 degrees C. UV-visible absorption spectroscopy, photoluminescence (PL), and the luminescence quantum yield of the Eu(III) complexes were measured and compared with each other, and the effect of different substituted-alkyls at N-position in the carbazole ring on the photoluminescence was discussed in details, indicating there exists a competition between the absorption capacity and the energy transfer efficiency for the complexes when the structure of the substituted-alkyls changes. The triplet state energy levels of the beta-diketonate ligands in the complexes are higher than that of the lowest excited level of Eu3+ ion, D-5(0), so the photoluminescence mechanism of the Eu(HI) complexes was proposed as a ligand-sensitized luminescence process. Red LEDs were fabricated by precoating the complexes onto 395 nm emitting InGaN chips. All the results show that this series of Eu(III) complexes is a promising candidate as a red component in fabrication of NUV-based white LEDs.