Polarized photoluminescence characteristics of rubrene sheets with nanometer thickness

Abstract

We report on the temperature dependence of the polarized photoluminescence (PL) exhibited by crystalline organic rubrene sheets with a thickness of similar to 60 nm. To probe the correlations between the electronic states and the molecular stacking of rubrene molecules, the polarized PL spectrum of a single rubrene sheet was analyzed as a function of temperature from 10 to 250 K. Drastic changes were observed in PL peak positions and intensities similar to 100 and similar to 170 K, which were likely related to variations in molecular ordering with temperature. The changes in the PL characteristics of the sheet similar to 170 K are similar to those observed for rubrene bulk crystals, in terms of the enhancement of mobility and crystallinity. In addition, similar to 100 K, the reversal of the relative ratio of PL intensities corresponding to two crystalline axes, a and b, in the rubrene sheets suggested an anisotropic variation in the molecular ordering along these two crystalline axes.