Characterisation of thin films of the organic infra-red emitters Yb- and Er-tris(8-hydroxyquinoline) by X-ray photoemission spectroscopy

Thin films of the rare earth tris(8-hydroxyquinolines) YbQ(3) and ErQ(3) were evaporated in ultra-high vacuum, and studied by X-ray photoelectron spectroscopy (XPS). Evaporation was monitored by mass spectroscopy of the major cracking products, which have masses >200 a.m.u. and show further splitting due to wide isotope distributions. C and N 1s XPS data are very similar to those of aluminium tris(8-hydroxyquinolines), implying very similar ligand behaviour, while the O 1s binding energy was significantly higher, indicating a more ionic metal-oxygen bond. YbQ(3) was found to be completely trivalent, with no indication of the mixed valence behaviour observed in other Yb compounds. (C) 2003 Elsevier Science B.V All rights reserved.