Abstract: To investigate the quantum effects on the absorption spectra of double concentric sodium nanoshells and compare them with the local response approximation model (LRAM) and hard-wall hydrodynamic model (HDM),the quantum hydrodynamic model (QHDM) was employed based on coupled-mode theory to analyze the coupling characteristics of resonance modes on the inner and outer surfaces of a single shell,as well as the surface plasmon resonance properties of double concentric sodium nanoshells.The results indicate that,for a single-shell structure,LRAM predicts that as the inner cavity radius increases,the low-energy mode redshifts while the high-energy mode blueshifts;when the shell thickness increases,the low-energy mode blueshifts while the high-energy mode redshifts.In the case of the double concentric sodium nanosphere shell structure,when the spacing between shells is large,the two high-energy modes predicted by the HDM model exhibit a significant blueshift compared to LRAM predictions,whereas the same modes predicted by the QHDM model show a substantial redshift.Furthermore,when the outer shell thickness is large,the two low-energy modes predicted by both HDM and QHDM exhibit a slight blueshift relative to LRAM predictions,while the two high-energy modes predicted by HDM show a significant blueshift and those predicted by QHDM demonstrate a significant redshift.

Key words: surface plasmonic, absorption spectrum, quantum hydrodynamic model, double concentric Na nanoshells