Formation and recombination of transient radical anions of Al, Ga, and In tris-8-oxyquinolinates (Alq(3), Gaq(3), and Inq(3)), the key species in certain organic electroluminescing devices, was studied in X-irradiated benzene solution. The spectra of recombination luminescence were obtained and effective yields of recombination luminescence referred to Alq(3) were estimated as 0.3 (Gaq(3)) and 0.15 (Inq(3)). Magnetic field effects in recombination luminescence involving the radical anions of the three oxyquinolinates were obtained, from which hyperfine coupling constants at the central ions were estimated as 0.45 (I-Al = 5/2), 0.8 (I-Ga = 3/2), and 0.6 (I-In = 9/2) mT for radical anions of Alq(3), Gaq(3), and Inq(3), respectively. (C) 2012 Elsevier B.V. All rights reserved.