Mn2+ doped ZnS quantum dots in ferroelectric liquid crystal matrix: Analysis of new relaxation phenomenon, faster optical response, and concentration dependent quenching in photoluminescence

Abstract

Phase transitional, dielectric, electro-optical, polarizing optical microscopic, photoluminescence (PL), and Fourier transformed infrared (FTIR) spectroscopic measurements have been carried out on ZnS:Mn quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC). A new dielectric relaxation mode has been envisaged in FLC material due to the presence of 0.25 wt. % ZnS:Mn (40 mol. %) QDs. The characteristics of the new mode have been compared with those of the soft mode. A significant fastening of the electro-optical response (∼75%) has been observed in the case of 0.25 wt. % ZnS:Mn (20 mol. %) QDs doped FLC material. The induction of the new relaxation mode is attributed to the flexoelectric tilt fluctuations. The induced flexoelectric polarization in the FLC medium at the vicinity of QDs might be responsible for the enhanced spontaneous polarization in the FLC/QDs mixtures. Quenching in PL for the FLC/QDs mixtures has been observed, which strongly depends on Mn content in QDs. The change in FTIR spectra for the FLC/QDs composite clearly indicates the change in molecular dynamics of the pure FLC after the dispersion of QDs. The presented results will certainly pave a way to utilize QDs for obtaining faster response of the FLC material and potential material to tune the relaxation processes.

Modifications of EHPDB Physical Properties through Doping with Fe2O3 Nanoparticles (Part II)

“…It cannot be ruled out that this process was related to certain movements of nanoparticle aggregates or the joint movement of LC molecules with the surrounding nanoparticles (or their aggregates). In turn, the relaxation frequency of the new high-frequency mode in Composite 4 ( Figure 9 c) was higher than that of GM, as it was observed for the relaxation process in Felix 17/100 doped with a higher concentration of ZnS QDs [ 38 ]. This relaxation process was attributed to the flexoelectric tilt fluctuations in the host in the vicinity of QDs, and it may be possible that for Composite 4, the origin of the new high-frequency relaxation mode was the same.…”

“…3.5 nm, 0.5, 1.0 and 2.0 wt %) onto Felix 16/100 was the emergence of a new relaxation mode (attributed to dipolar interactions between FLC molecules and quantum dots) depending on their concentration, as well as the modification of the GM relaxation frequency [37]. In turn, the new relaxation process observed by doping Felix 17/100 with ZnS QDs was attributed to the flexoelectric tilt fluctuations in the FLC next to QDs [38].…”

“…3.5 nm, 0.5, 1.0 and 2.0 wt %) onto Felix 16/100 was the emergence of a new relaxation mode (attributed to dipolar interactions between FLC molecules and quantum dots) depending on their concentration, as well as the modification of the GM relaxation frequency [ 37 ]. In turn, the new relaxation process observed by doping Felix 17/100 with ZnS QDs was attributed to the flexoelectric tilt fluctuations in the FLC next to QDs [ 38 ]. Finally, it should be noted that the excess of nanoparticles in the created nanocomposites may destroy or strongly disturb the liquid crystal order, which in turn may lead to the uselessness of the created hybrid materials.…”

Magnetic Control of the Manganese Photoluminescence in Fe3O4/l-Cys ZnS:Mn Nanocomposites

“…This process changes surface defect (vacancy) states for energy transfer that in turn reduce the influence of Mn 2+ . The whole effect results in lowering the amount of 4 T 1 – 6 A 1 transitions. , …”

“…The whole effect results in lowering the amount of 4 T 1 − 6 A 1 transitions. 29,34 We have studied the ML effect of Fe 3 O 4 /L-cys ZnS:Mn in the presence and absence of an external magnetic field (1.0 T) in the temperature range of 10−300 K. ML measurements were performed by applying a static magnetic field on the longitudinal plane of Fe 3 O 4 /L-cys ZnS:Mn, above and below its superparamagnetic ordering temperature. Prominent and reproducible ML coupling was observed at various temperature ranges, as depicted in Figure 5.…”