Investigations on Liquid Crystal Embedded CdTe Quantum Dots with Spectrally Resolved Confocal Laser Scanning Microscopy

Liquid crystals (LCs) represent the backbone of multiple industries given their superb capabilities to modify their optical properties under electric, magnetic, thermal, or mechanical stimuli [1],[2]. Their in-depth understanding is critical for advancing further the state-of-the-art on LC synthesis, for enhancing their current uses, and for the advent of novel LC-based solutions capable to solve important pending problems in various field of science and industry. The dispersion of quantum dots (QDs) into LCs has been demonstrated in past works [3]-[6] as a highly valuable avenue to enhance the electro-optical properties of LCs and to produce efficient tunable electro-optical devices such as quantum-dot lasers or emission modulators. Many studies showed to date that the chemical composition and the phase (isotropic, nematic, cholesteric) of a liquid crystalline environment hold an important influence over the emissivity of embedded QDs. On the other hand, the QDs are known to influence the properties of the host, by increasing or decreasing its response time, depending on the anchoring strength of the molecules on their surface. This interdependence is known to be valuable for implementing diverse photonic microdevices, whose properties can be tuned via this interplay between the properties of the LC host and embedded QDs. Confocal Laser Scanning Microscopy (CLSM) is generally acknowledged as a superb optical investigation tool, given its high-resolution, high acquisition speed, optical sectioning capabilities and possibilities for specific contrast. CLSM has been successfully used to date to investigate both QDs [7], and LCs [8]. It represents thus an excellent investigation method to probe the distribution of QDs in an LC template, and to resolve their properties spatially and spectrally. In this work we employ a CLSM system equipped with a spectral option to evaluate the emission spectra of QDs dispersed in an LC environment. Namely, we investigate the emission spectra of green, yellow and red emitting CdTe QDs, for both pristine and N-(4-Methoxybenzylidene)-4-butylaniline (MBBA) LC embedded instances. With this effort, we try to assess the influence of LC on the optical properties of CdTe QDs, and whether this influence is the same for QDs with similar chemical composition, but with different emissive properties. Under UV illumination matching the absorption band of the CdTe QDs, we observe minor modifications in the emission spectra for the green and yellow emitting CdTe QDs, whereas for the red-emitting CdTe QDs the emission in the initial band is quenched, but instead we notice a significant emission in blue. Our future work will focus on achieving a better understanding of the anchoring mechanisms of MBBA molecules on the surface of the CdTe QDs, and for resolving the composite’s properties, whose tunability could be important for the optimization of various devices.