Dependence of Resonance Energy Transfer on Exciton Dimensionality

We investigate the dependence of resonance energy transfer from Wannier-Mott excitons to an organic overlayer on exciton dimensionality. We exploit the excitonic potential disorder in a single quantum well to tune the balance between localized and free excitons by scaling the Boltzmann distribution of excitons through temperature. Theoretical calculations predict the experimentally observed temperature dependence of resonance energy transfer and allow us to quantify the contribution of localized and free excitons. We show that free excitons can undergo resonance energy transfer with an order of magnitude higher rate compared to localized excitons, emphasizing the potential of hybrid optoelectronic devices utilizing resonance energy transfer as a means to overcome charge transfer related limitations.

Figure 1

Hybrid organic-inorganic configuration. (a) Spectral overlap between QW emission (blue line) and polyfluorene absorption (black dashed line). Red dotted line: polyfluorene emission. (b) Schematic of the hybrid configuration. (c) Spectral broadening and shift of QW emission with increasing temperature. Black solid line, without polyfluorene; red interrupted line, with polyfluorene. The emission spectrum shows a contribution from the $1\mu \mathrm{m}$ thick GaN buffer layer.

Figure 2

Spectroscopic evidence of RET. (a) Photoluminescence decay of the QW before (black lines) and after (red lines) deposition of polyfluorene. The two lowermost graphs correspond to the control sample with a thicker capping layer. (b) Temperature dependence of exciton recombination in the QW before (black triangles) and after (red circles) deposition of polyfluorene. (c),(d) Energy transfer rate and efficiency vs temperature. The black line in (c) is the modeled temperature dependence. (e) Photoluminescence transient of the polyfluorene deposited on samples with a 4 (red dotted line) and 9 nm (black line) capping layer.

Figure 3

Distribution of excitonic states in the imperfect QW. (a) Schematic of the random potential experienced by QW excitons and its harmonic approximation. (b) Density of states composed of a delta function for localized excitons and a flat contribution for free excitons in the QW (relative contributions not drawn to scale). (c) Population of localized (blue dashed line) and free (red line) excitons vs temperature. (d) Calculated RET rate for localized excitons (blue dashed line) and free excitons at 130 K (red line) for varying thickness of the capping layer. The dotted green line corresponds to the RET rate of the exciton with the optimum wave vector for each thickness. The thin horizontal line marks the exciton decay rate at 130 K without RET. (e) Temperature dependence of the Förster radii of localized (blue dashed line), free (red line), and excitons with the optimum wave vector (green dotted line).