Photoluminescence efficiency and absorption of aluminum-tris-quinolate (Alq(3)) thin films

Absorption, photoexcitation and internal and external luminescence efficiencies for Alq(3) films grown by vacuum deposition have been measured accurately for the first time. The absorption spectrum measured at wavelengths between lambda = 250 and 450 nm is due to the overlap of the (1)L(a) (385 nm) and B-1(b) (260 nm) transition bands found in the solution spectrum of Alq(3). The efficiency of the prominent luminescence band centered at lambda = 530 nm was observed to be independent of the excitation wavelength in the spectral range between lambda = 250 and 450 nm. The internal quantum efficiency was found to be (32 +/- 2)% independent of film thickness from 100 Angstrom to 1.35 mu m, indicating a very short diffusion length for the (1)L(a), and B-1(b), excited states.