Tuneability of amplified spontaneous emission through control of the thickness in organic-based waveguides

Abstract

The thickness dependence of amplified spontaneous emission (ASE) in optically pumped polystyrene films containing 15 wt % of the luminescent and hole-transporting organic molecule N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) is reported. It is observed that the position of ASE can be tuned between 404 and 417 nm by changing the film thickness from 100 to 200 nm. By measuring and modeling the waveguide modes, we demonstrate that the calculated cut-off thickness for the propagation of one mode determine the thickness below which ASE disappears although they do not perfectly correlate with the observed wavelength shifts. Results show that the position of ASE depends on the shape of the photoluminescence spectrum, that is composed of various vibronic peaks whose relative intensities change with film thickness due to the existence of the cut-off thickness. Finally, it is also observed that both the position and the threshold of ASE depend on the different confinement of the propagation modes due to thickness variations.