Photocalorimetric study on nonradiative relaxation processes and photoluminescence quantum yields in Alq3 single crystals

Heat generation caused by nonradiative relaxation processes in tris-8-hydroxyquinoline aluminum (Alq(3)) was measured at 2 K by using a photocalorimetric (PC) detecting system. At lower temperatures, the photoluminescence (PL) quantum yield is much higher than that at room temperature because of the quenching of thermal disturbance. At 2 K, the PL quantum yield of a single crystal specimen and of a vapour-deposited thin film of Alq(3) was estimated to be 0.76+/-0.03 and 0.79+/-0.03, respectively, under excitation above the absorption edge. On the other hand, under excitation below the absorption edge, a weak PC signal response is clearly resolved, even in the highest quality single crystal, indicating the existence of nonradiative recombination centres in the transparent energy region. (C) 2004 Elsevier B.V. All rights reserved.