Study of optical properties of TRIS (8-hydroxyquinoline) aluminum (III) Pawel Dalasin ´ski * , Zbigniew Lukasiak, Michal Wojdyla, Mateusz Re ßbarz, Waclaw Bala Institute of Physics, UMK, Grudzia ˛dzka 5, 87-100 Torun ´ , Poland Received 28 September 2004; accepted 7 October 2004 Available online 4 June 2005 Abstract In this article, we present photoluminescence (PL) properties of tris (8-hydroxyquinoline) aluminum(III) (Alq 3 ) layers. The refractive index, absorption coefficient and layer thickness were determined from reflection (R) and transmission (T) spectra. Ó 2005 Elsevier B.V. All rights reserved. PACS: 78.20.Ci; 78.55.m Keywords: Alq 3 ; Photoluminescence; Reflection; Absorption; Refractive index 1. Introduction Alq 3 enjoys more and more popularity among scien- tists due to his interesting optical and electrical features like great mobility of carriers, strong luminescence, high electric conductance, low cost and simple technology of fabrication. From this reason this compound is very attractive for optoelectronic applications such as photo- detectors, OLEDs, flat and flexible colour displays, pho- tovoltaic cells, etc. In spite of that first Alq 3 based organic light emitting diodes have been already con- structed [1], some physical problems are still not fully understood. In this paper, we investigate the transmis- sion and reflection spectra of Alq 3 layers grown on glass substrates and we estimate the refractive index, absorp- tion coefficient and layer thickness from these measure- ments. We also present here the photoluminescence emission and excitation spectra. 2. Experimental Alq 3 layers were prepared by thermal evaporation deposition method from quartz effusion cells on glass substrate. The process of preparing has been carried out under pressure about 2 · 10 5 Tr and at the temper- ature of the Alq 3 source about 430 K. Molecular struc- ture of Alq 3 is presented in Fig. 1. PL spectra were measured in the temperature range from 15 K to 330 K using helium refrigerator. As sources of excitation CdHe (measurements at different temperatures) or nitro- gen laser (room temperature measurement) were used. Halogen lamp was used for R and T spectroscopy. The photomultiplier R928 Hamamatsu (PL) and Si pho- todiode (R, T) were used as detectors. Reflection and transmission measurements were performed from 400 nm to 1200 nm spectral range. We used SPM2 Si prism monochromators for spectral selection. 3. Results and discussion Refractive index of investigated layer was calculated using envelope method proposed by Minkov [2]. This 0925-3467/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2004.10.031 * Corresponding author. Tel.: +48 56 661 3243; fax: +48 56 622 5397. E-mail address: dalas@phys.uni.torun.pl (P. Dalasin ´ ski). www.elsevier.com/locate/optmat Optical Materials 28 (2006) 98–101