Effect of film thickness on photoluminescence in bi-layer films
Xuan Long Ho1*, Jonathon David White1
1Department of Photonics Engineering, Yuan Ze University, Taoyuan, Taiwan
* presenting author:Long Ho, email:draloca@gmail.com
While multilayer films find application in many organic based devices, only limited work has been done to explore the effects of the thickness of these buffer layers on photoluminescence (PL) in the active layer. In order to investigate these effects, we created bilayer films by first spin-casting PMMA onto a glass substrate followed by a thin polystyrene (PS) layer doped with Rhodamine 6G. We then investigated the effects of buffer layer thickness (PMMA) on both the spectra and lifetime of the PL. As the buffer layer thickness increased from 0 to 140nm the PL spectra shifted slowly to the blue. Around 140nm there was a dramatic shift to the blue, after which the spectra remained constant. A similar effect was seen in the PL lifetime, with a slow increase in lifetime as the thickness increased to 140 nm at which point there was a sudden 250% increase in the flourescence lifetime. Above 140nm the PL lifetime was thickness independent. We believe that this is due to changes in the effective refractive index of bi-layer sample as the buffer layer thickness increases.

Keywords: bilayer film, buffer layer, thickness, photoluminescence, PL lifetime