Spectral and polarization modulation of quantum dot emission in a one-dimensional liquid crystal photonic cavity

Abstract

We demonstrate spectral and polarization modulation of chemically synthesized core-shell CdSe/ZnS quantum dots (QDs) embedded in a one-dimensional photonic cavity formed by a cholesteric liquid crystal (CLC) matrix. A Cano-wedge cell varies the pitch of the CLC leading to the formation of Grandjean steps. This spatially tunes the photonic stop band, changing the resonance condition and continuously altering both the emission wavelength and polarization state of the QD ensemble. Using high resolution spatially and spectrally resolved photoluminescence measurements, we find that the emission is elliptically polarized and that the tilt of the ellipse, while dependent on the emission wavelength, additionally varies with distance across the Grandjean steps. This work opens up the possibility of designing new QD based optical devices, such as tunable single photon sources, where spatial control of wavelength and polarization of the embedded QDs would allow great flexibility and added functionalities.

Quantum Dot/Liquid Crystal Nanocomposites in Photonic Devices

“…When the devices shown in Figure 3 were excited with the 532 nm continuous wave laser, we observed characteristic emission for QDs coupling with the cholesteric cavity for both types of particle (Figure 3e,f). The results are consistent with recent reported data from our group for ODA-QDs only [19,20]. In the ODA-QD device we observed that good cavity coupling as shown in Figure 3e as an example was very location dependent.…”

Tuning Quantum‐Dot Organization in Liquid Crystals for Robust Photonic Applications

“…In cholesteric devices, embedded QDs can act as emitters coupled to a tunable fluid cavity, producing applications such as the quantum dot liquid crystal laser [32] and switchable cavities able to spatially modulate QD emission. [29,31] The efficiency of such devices will depend on our control of co-operative effects between adjacent particles. For example energy transfer processes such as FRET can reduce the efficiency of QD cavity coupling if the particles are closely packed in aggregates.…”

“…This technique, applied previously by our group, [29][30][31] produces PL intensity maps of a 1 mm thick slice combined with emission spectra for each pixel recorded. PL microscopy provides a unique method for characterizing the distribution of fluorescent particles in liquid crystals, as energy-transfer processes, such as Forster resonance energy transfer (FRET), can be detected.…”

Quantum dots as liquid crystal dopants

“…Another example of the assembly of QDs in nematic 5CB has been discussed by Ghosh and co-workers. [105][106][107] They have shown that nanodisks of GaSe at concentrations up to 10% assemble into ordered aggregates each composed of 15-60 GaSe nanodisks in the nematic phase of 5CB. 105,106 Emission spectra, optical textures and size distribution of GaSe clusters in the NLC mixture are shown in Fig.…”