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 pin, 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 Tside≅130–270 °C) was the re-condensed Alq3, while that in the upper zone (Tside around room temperature) was the decomposed 8-hydroxyquinoline (8Hq). With increasing pin from 1.3×102 to 9.3×104 Pa, the decomposition of Alq3 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 Alq3 CSS zone on the initial phase of the source powder was observed and discussed.

► Constitutional supersaturation in a vapor transport ampoule was studied.
► Re-condensation and decomposition of Alq3 and formation of 8Hq needle crystals were discussed.
► This study is related to problems about Alq3-based OLEDs and organic crystal growth behaviors.