Quantum dots are an interesting photophysical system because photoluminescence from an individual QD can be used to selectively excite a larger QD in the sample. This process of self-absorption of photoluminesced light within a medium is an effect known as the inner filter effect (IFE). The IFE has been well studied in solutions, but has garnered less attention in regards to solid-state nanocomposites. In CdSe/CdS core/shell QD-polymer nanocomposites we observe a large spectral red-shift of over a third of the linewidth of the photoluminescence of the nanocomposites over a distance of 100 μm resulting from the IFE (Fig. 1). Unlike fluorescent dyes, which do not show a large IFE red-shift, QDs have a component of inhomogeneous broadening that originates from their size distribution and intrinsically variable photophysics. By controlling the photoluminescence broadening as well as sample dispersion and concentration, we show that the magnitude of the IFE within the nanocomposite can be tuned. We further demonstrate that this shift can be exploited in order to spectroscopically monitor the vertical displacement of a nanocomposite in a fluorescence microscope. Large shifts in the measured emission with displacement can be maximized resulting in a displacement sensor with sub-micrometer resolution. We further show that the composite can be easily attached to biological samples and is able to measure deformations with high temporal and spatial precision.

Characterizing the inner filter effect in quantum dot-polymer composites for use as a displacement sensor

253rd National Meeting (2017)

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