# Perspectives in Liquid-Crystal-Aided Nanotechnology and Nanoscience
## 3 Photonic Applications
Among the various methods, one feasible approach is combining plasmonic units with host matrixes whose dielectric characteristics can be manipulated through external stimuli [254]. To this end, LCs have come into the spotlight. LCs hold great potential for enabling effective manipulation over the optic characteristics of plasmonic architectures due to their large refractive index anisotropy, real-time response to the external stimuli and the unique ability to act as dynamic templates for the self-assembly of nanomaterials. As a result, LCs have been widely used to manipulate SPR effects, not only in nanoparticles, but also in binary gratings, antenna arrays, patterned conductive surfaces and metamaterials. To date, a wealth of gold nanoparticle-LC composites with tunable SPR have been reported [254; 255; 256; 81; 82; 257; 81; 82; 258; 259; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 110; 111; 112; 113; 114; 115; 116;  
Another possible SPR effect, which is attractive but as yet largely unexploited, arises from the design and realization of tunable emissive materials, in which the SPR-related losses of light can be compensated for by the corresponding enhancement effect. For instance, in [238], nanoparticles composed of gold cores and dye-doped silica shells could efficiently offset the loss of SPR through the gain of dyes, thus enabling surface plasmon amplification by stimulated emission of radiation. Based on this idea, the authors of [267] successfully realized the control of both the intensity and decay rates of fluorescence by combining the absorption of SPR and the fluorescence anisotropy of dyes (Figure 9). In this system, the LC medium acts as an active template, imposing orientational ordering on the nanorods and mediating synchronous switching of the anisotropic particle orientation. Although gold nanoparticles have been widely used as plasmonic building blocks for various plasmonic optical applications, they are rarely applied in applications such as optical shutters, smart windows or spatial light modulators. The main reason is due to the confinement of the size and shape. The SPR peaks of these gold nanoparticles are normally limited to within the near-infrared (NIR) spectral range. One effective solution to this problem was put forward by [PERSON] et al. [268]. They developed a guest-host mesostructured composite in which dye molecules and plasmonic nanorods spontaneously aligned either parallel or orthogonally to the director of the LC (5 CB and AMLC-0010) host. Such a system allows the feasible tunability of the SPR peaks from the NIR to the visible spectral range. By changing the geometry of nanoparticles and different kinds of LC materials (nematic and cholesteric LCs), the authors also showed that the switching time of the composite could be tuned from milliseconds to seconds and even the polarization of the transmitted light could be manipulated according to the application demands. Another solution, which was proposed by the same group, was co-dispersing different anisotropic nanoparticles in LCs [269]. The authors used gold nanorods with varying aspect ratios in a nematic LC host (5 CB). By applying appropriate surface treatments to the particles, the nanorods oriented either parallel or orthogonal to the LC director. With the application of an electric field, the nanorods would rotate their short or long axes due to elastic coupling between particles and the LC director, thus leading to a tunable SPR spectral range as well as polarization-dependent optical characteristics. Figure 8: Extinction measurement of gold-nanorods (GNRs)/8 CB samples deposited on a PVA polymer with (**a**,**d**) nonpolarized incident light and with an incident light polarized (**b**,**e**) parallel and (**c**,**f**) perpendicular to the oily streaks. Reproduced with permission from [266]. Copyright (2017) American Chemistry Society.