Interfacial chemistry of samarium (Sm) with tris-(8-hydroxyquinoline) aluminum (Alq(3)) has been investigated. Photoelectron analysis revealed strong interactions at the Sm-Alq(3) interface and limited Sm diffusion into Alq(3). The lowest unoccupied molecular orbital of Alq(3) was found to be 0.28 eV below the Fermi level of Sin at the Sm-Alq(3) contact, implying lacking a barrier to electron-injection from the Sm to Alq(3). Replacing Sm for MgAg as a cathode in organic electroluminescent devices considerably improved current-voltage characteristics, while the device efficiency was found to decrease by 40%. The reduction in efficiency is attributed to low optical reflectance at the Sm-Alq(3) interface. (C) 2003 Elsevier Science B.V. All rights reserved.