Nanoparticle surface energy transfer (NSET) in ferroelectric liquid crystal–metallic-silver nanoparticle composites: Effect of dopant concentration on NSET parameters

In the recent past, the resonance energy transfer studies using metallic nanoparticles has become a matter of quintessence in modern technology, which considerably extends its applications in probing specific biological and chemical processes. In the present study, metallic-silver nanoparticles of 2–4 nm (diameter) capped with hexanethiol ligand are developed and dispersed in ferroelectric liquid crystal (FLC). The morphology of nanoparticles was characterized using HR-TEM and SEM techniques. Furthermore, a systematic study of energy transfer between the host FLC material (as donors) and metallic-silver nanoparticles (as acceptors) has been explored employing steady state and time resolved fluorescence spectroscopic techniques. The nanoparticle based surface energy transfer (NSET) parameters viz., transfer efficiency, transfer rate, and proximity distance between donor and acceptor, have been determined for NSET couples (FLC material–metallic-silver nanoparticle) composites. It is observed that various NSET parameters and quenching efficiency follow a linear dependence on the concentration of metallic-silver nanoparticles in host FLC material. The nonradiative energy transfer and superquenching effect were analyzed with the help of Stern-Volmer plots. The impact of present study about superquenching effect of the silver nanoparticles can be used for sensing applications that require high degree sensitivity.

Figure 1

UV absorbance of host FLC material (${\mathbf{S}}_{\mathbf{0}}$) and FLC composites having metallic-silver nanoparticles in 0.1, 0.3, and 0.5 (wt./wt.)% concentration (${\mathbf{S}}_{\mathbf{1}}$, ${\mathbf{S}}_{\mathbf{2}}$, ${\mathbf{S}}_{\mathbf{3}}$). Absorbance study has been performed in colloidal state (at room temperature) by taking HPLC grade toluene (mg/ml) as solvent.

Figure 2

(a) Fluorescence spectra of ${\mathbf{S}}_{\mathbf{0}}$ (pure FLC material) and ${\mathbf{S}}_{\mathbf{1}}$, ${\mathbf{S}}_{\mathbf{2}}$, ${\mathbf{S}}_{\mathbf{3}}$ (FLC–metallic-silver nanoparticles composites). (b) The Gaussian fit of the fluorescence spectra of ${\mathbf{S}}_{\mathbf{0}}$ (pure FLC material).

Figure 3

Spectral overlap between fluorescence spectra of pure FLC (blue circle) and absorption spectra of metallic-silver nanoparticles [Ag dopant (red square)], at room temperature.

Figure 4

Time-resolved decay profile of pure FLC material (${\mathbf{S}}_{\mathbf{0}}$) along with FLC–metallic-silver nanoparticles composites (${\mathbf{S}}_{\mathbf{1}}$, ${\mathbf{S}}_{\mathbf{2}}$, ${\mathbf{S}}_{\mathbf{3}}$) at room temperature.

Figure 5

Average decay lifetime of host FLC material as a function of metallic-silver nanoparticles concentration in host LC material.

Figure 6

The time resolved Stern-Volmer plot for NSET pair: Host FLC material–metallic-silver nanoparticles.