Photoluminescence spectroscopy study on tris(8-hydroxyquinoline) aluminum film

In situ photoluminescence spectroscopy (PL) measurements of tris(8-hydroxyquinoline) aluminum (Alq3) film were carried out. Upon deposition of Alq3 on the glass substrate, the PL intensity changes dramatically, while the peak position of Alq3 emission shows a sharp red-shift from 524 nm at the initial deposition of Alq3, and tends to a saturation value of 536 nm for the film thickness range from 2 to 500 nm. This red-shift is associated with the change from the 2D to 3D exciton state with increasing Alq3 film thickness. Temperature dependent PL spectra of Alq3 films showed, besides the changes in the PL intensity, clearly a blue-shift of Alq3 emission about 9 nm for the film annealing up to 150 °C, while no any shift of Alq3 emission was observed for the film annealing below 130 °C. Both changes in PL intensity, and especially in the peak position of Alq3 emission were attributed to crystallization (thermal) effect of Alq3 film upon annealing.