F. Papadimitrakopoulos et Xm. Zhang, ENVIRONMENTAL STABILITY OF ALUMINUM TRIS(8-HYDROXYQUINOLINE) (ALQ(3))AND ITS IMPLICATIONS IN LIGHT-EMITTING DEVICES, Synthetic metals, 85(1-3), 1997, pp. 1221-1224
The thermal stability of the aluminum tris(8-hydroxyquinoline) (Alq(3)
) is currently discussed, in light of its vital role in failure mechan
isms of molecular-based light emitting diodes (LEDs). This was investi
gated with the use of gas chromatography/mass spectroscopy (GC/MS), as
sisted by a specialized accessory that permits heating of powders or t
hin films of Alq(3) under a controlled environment. We have shown that
at elevated temperatures, Alq(3) undergoes a ligand exchange reaction
with water, which readily adsorbs on its surface. The increased sensi
tivity of CC/MS in detecting the liberated 8-hydroxyquinoline (8-Hq) i
ndicates that Alq(3) is extremely sensitive to the moisture above 90 d
egrees C. The surface of a freshly sublimed Alq(3) powder or film beco
mes saturated with water in less than 2 minutes, under normal laborato
ry conditions. The implications of the underlying chemistry are discus
sed in relation to failure mechanisms observed in Alq(3) based LEDs.