A new class of media with abnormal electromagnetic parameters has been attracting increasing attention because of its exotic properties and potential application.Currently,typical metamaterials are mainly composed of artificially designed metallic periodic structures.However,due to the limitations of available fabrication technologies,physical size and material effects,it is difficult to realize these abnormal properties by these artificial structures in the high-frequency regime.Therefore,it is important to find materials with intrinsic abnormal electromagnetic responses.In this field,a new mechanism based on the interaction between polar lattice vibrations and electromagnetic waves has been proposed.In this paper,we review progress in this field.
Metal-enhanced fluorescence(MEF)from lanthanide chelates in close proximity to silver films was studied.Different thicknesses of silver films(20 and 50 nm)were deposited onto quartz substrates using magnetron sputtering,while silver island films were prepared using a previously published procedure.Obviously enhanced emissions from the lanthanide chelates were observed on the silver films.The effect of using different concentrations of aqueous solutions polyvinyl alcohol(PVA)on MEF was also investigated.Fluorescence close to a 20-nm-thick silver film showed that the enhancement of emission is a function of the thickness of the PVA film,reaching a maximum(～2.5-fold increase in intensity)at 83 nm.In conclusion,the MEF induced by the silver films is caused by an electric field effect arising from surface plasmon resonance.
