We report the fabrication of symmetrically configured alternating-current (ac) light-emitting devices based on tris-(8-hydroxyquinoline) aluminum (Alq(3)). The devices consist of an emissive layer of Alq(3) sandwiched between two layers of silicon dioxide. A blue emission at 457 nm could be obtained from the devices under the ac driving. The blue emission corresponds to the direct recombination from the lowest unoccupied molecular orbital (LUMO) to the highest occupied molecular orbital (HOMO) of Alq(3). According to the dependence of luminescent intensity on the voltage and frequency, we ascribed this direct recombination to the dissociation of Frenkel excitons and the charge accumulation at the interface of SiO2 and Alq(3).