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

Abstract By choosing various crystalline forms of tris(8-hydroxyquinoline)-aluminum (Alq 3 ) 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 °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 ≅130–270 °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 1.3×10 2 to 9.3×10 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.