Figure 3

(a) Visible-NIR absorption spectra of the samples without Yb3+ ions. The samples with GNPs clearly show a resonance band. (b) Visible-NIR absorption spectra of the samples doped with Yb3+ ions and GNPs or SNPs. The samples with GNPs clearly show a resonance band. Inset: deconvolution of the Yb3+ ion absorption band (2F7/2 level) showing its four Stark splitting.