Photoluminescence efficiency and absorption of aluminum-tris-quinolate (Alq3) thin films

Absorption, photoexcitation and internal and external luminescence efficiencies for Alq3 films grown by vacuum deposition have been measured accurately for the first time. The absorption spectrum measured at wavelength between λ = 250 and 450 nm is due to the overlap of the 1La (385 nm) and 1Bb (260 nm) transition bands found in the solution spectrum of Alq3. The efficiency of the prominent luminescence band centered at λ = 530 nm was observed to be independent of the excitation wavelength in the spectral range between λ = 250 and 450 nm. The internal quantum efficiency was found to be (32 ± 2)% independent of film thickness from 100 Å to 1.35 μm, indicating a very short diffusion length for the 1La and 1Bb excited states.