Thin Solid Films 417 (2002) 72–74 0040-6090/02/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0040-6090 Ž 02 . 00597-7 Improvement of environmental stability of aluminum tris(8- hydroxyquinoline) thin films G. Baldacchini , T. Baldacchini , S. Gagliardi , R.M. Montereali , A. Pace , R.B. Pode * a b a a a c, ENEA, Frascati Research Centre, Via E. Fermi, 45, P.O. Box 65, 00044 Frascati, Rome, Italy a Chemistry Department, Boston College, Chestnut Hill, MA 02135, USA b Physics Department, University of Nagpur, Nagpur 440 010, India c Received 18 April 2002; accepted 17 June 2002 Abstract It is argued that some organic materials play an important role in preventing the formation of nonemissive species and enhancing the intrinsic stability of Alq thin films. In the present work, films (Alq pure, Alq qORGMAT (top), and Alq doped 3 3 3 3 with same) were grown on glass and silica substrates by thermal evaporation. Excitation, fluorescence, and transmission spectra have been measured, and the intensity of the green photoluminescence as a function of time has been monitored. Preliminary results show an improved stability of the emission in the doped Alq films compared with the undoped ones. 3  2002 Elsevier Science B.V. All rights reserved. Keywords: Doped organic thin films; Environmental stability; Emission; Excitation 1. Introduction Organic materials such as small molecules are attract- ing much attention as candidates for flat panel displays and semiconductor applications, because of their effi- cient electroluminescent properties. Among them, the tris-(8-hydroxyquinoline) –aluminum complex, Alq , is 3 the most important and widely studied material. The organic light emitting diode (OLED) can be a complex structured device, but the light emitting material remains the key element in its architecture. The electrical and optical properties of these materials have been studied in detail since the discovery of the first efficient multi- layer device, which used Alq w1x. However, the device 3 reliability and stability still remains a challenging issue. The stability of OLEDs has always been a primary subject for both basic and applied research. It was found that Alq is very much sensitive to moisture and oxygen, 3 which produce nonemissive species acting as lumines- cence quenchers w2x. However, the stability of Alq - 3 based OLEDs has been improved by doping the emitting layer with various organic materials, mostly dyes w3x. *Corresponding author. Fax: q91-712-532841. E-mail address: rbpode@yahoo.com (R.B. Pode). In this work, absorption and emission spectra have been measured in thin films of pure Alq , Alq q 3 3 ORGMAT (top layer) and Alq doped with ORGMAT 3 w4x. The ORGMAT material is derived from the big phenol family, which has been widely used to arrest the degradation of many organic compounds. The stability of Alq films against atmospheric moisture and oxygen 3 is studied by measuring the intensity of fluorescence as a function of time. 2. Experimental details Films (Alq pure, Alq qORGMAT as top layer, and 3 3 Alq doped with ORGMAT material) were grown on 3 glass and silica substrates by thermal evaporation. The starting powder was supplied from Merck chemical products of nominal purity more than 99%. Both pow- ders, Alq (350 8C, melting temperature without decom- 3 position) and dopant ORGMAT (70 8C, melting point) were mixed thoroughly in the proportion of 95:5 by wt. and then transferred into a molybdenum crucible used for the evaporation. The substrates were kept at room temperature (RT) on a copper holder. The pressure in the evaporation chamber was of the order 10 Torr. y6 The mixed powders were kept just below the sublimation