Figure 2

(a) Optical absorption spectra of Pr\(^{3+}\) singly doped and Pr\(^{3+}\)/Yb\(^{3+}\) co-doped glasses, and sun radiation AM1.5 spectrum; (b) absorption intensity of Yb\(^{3+}\): \({^2F_{7/2} \rightarrow ^2F_{5/2}}\) transition, and (c) integrated intensity of \({^2F_{7/2} \rightarrow ^2F_{5/2}}\) transition as a function of Yb\(^{3+}\) ions.