Re-condensation and decomposition of Tris(8-hydroxyquinoline)-aluminum in a vapor transport ampoule

By choosing various crystalline forms of tris(8-hydroxyquinoline)-aluminum (Alq3) source powders and using different transport gases under various inside-pressures p(in), two constitutional supersaturation (CSS) zones were observed in a vapor transport ampoule with a source temperature of 300 degrees C and a growth period of 5.0 h. From UV-visible spectra, the material in the lower CSS zone (with sidewall temperature T-side congruent to 130-270 degrees C) was the re-condensed Alq(3), while that in the upper zone (T-side around room temperature) was the decomposed 8-hydroxyquinoline (8Hq). With increasing p(in) from 1.3 x 10(2) to 9.3 x 10(4) Pa, the decomposition of Alq(3) into 8Hq was enhanced, and the deposition of 8Hq CSS zone became apparent with the formation of several 8Hq needle crystals. In addition, a dependence of the crystal structure formed in the Alq(3) CSS zone on the initial phase of the source powder was observed and discussed. (C) 2012 Elsevier B.V. All rights reserved.