The complexes of europium(III) with 4,6-diacetylresorcinol (H(2)DAR) and a co-ligand (phen, bpy or 2,2'-bipyridille N,N'-dioxide (2,2'-bpyO(2))) were in situ synthesized in silica matrix via a two-step gel process. The formation of complexes in silica gel was confirmed by the luminescence excitation spectra. The silica gels that contain in situ synthesized europium complexes exhibit the characteristic emission bands of the Eu(III). The results show that there are two ways to enhance the emission intensity of the Eu(III): (i) synthesize the complex in silica matrix and (ii) synthesize the complex with a co-ligand, which coordinates with Eu(III) in the composite system and can efficiently transfer the energy from 4,6-diacetylresorcinol to the Eu(III). The order of the luminescence intensities of the complexes is: Eu-2(DAR)(3)(phen)(2)-(sol-gel) > Eu-2(DAR)(3)(2,2'-bpyO(2))(2)-(sol-gel) > Eu-2(DAR)(3) (bpy)(2)-(Sol-gel > Eu-2(DAR)(3)-(sol-gel) > pure Eu-2(DAR)(3).4H(2)O. (C) 2007 Published by Elsevier Ltd.