Localized Plasmon Resonance (LPR)

The radiation from the sun comprises of 46% visible light and 49% Infrared Waves. There has been an increasing demand for heat barrier films in the recent times. These films are fixed to the windows and reduce the transmission of infrared radiation. The most popular films are those which are able to reduce the transmission of infrared radiation while still allowing visible light to pass through.

 As almost half of the solar energy comes from infrared region i.e. 800nm to 1100nm wavelength.

Therefore materials that can reduce the amount of infrared transmission is in popular demand. Of these infrared blocking materials, the ones that reflect the radiation are better than the ones that absorb the radiation. This is because the radiation absorbed by the material will allow some of the heat to radiate into room.

To come up with a model that achieves the desired properties, we needed to look at the metamaterials based on the concepts of Localized Plasmon Resonance (LPR).

LPR descibes the collective motion of free electrons of metal atoms in resonance with the vibration of the electric field of light. Light is absorbed and scattered very strongly near the resonant frequency. It is, however, achievable to control the frequency of LPR and the tendencies of the light that is scattered with the help of different arrangements, sizes and shapes of various metallic nanostructures.LPR arises most promptly in the precious metals which have low electrical resistance, with Silver known to have causing the strongest amount of LPR.

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Also, Silver exhibits a very high refelctivity value. Silver mirrors have been around since ages and is used in households. But here, we also need to talk about the reflection of infrared waves along with visible light. Even the plasmonic particles of Gold shows LPR within the precinct of visible and near infrared spectrum.

Dielectric coatings reflect light by constructive interference through the different layers of dielectric material. Anti-reflective coatings are also based on the same principle but destructive interference is observed. The shape of the nanoparticles is an important parameter to control resonance wavelengths. Round silver particles are known to be resonant with visible light. However,when shaped into f lat disks, silver nanoparticles can be resonant with a wider range of wavelengths from visible light to infrared light5).

In the experiments conducted before by scientists at Fujifilm, The best results were achieved when the area packing of silver nanoparticles was 35% and the nanoparticles were arranged like stones on the sidewalk without any overlapping. Therefore for our experiment, we have chosen the materials and their dimensions to build upon the already conducted successful experiments done by other researchers and scholars in this field and add onto the already existing knowledge.