## 3 Results and Discussion
It should be noted that, under UV excitation, the emission spectra of R-PE/PVA and R-PE/alginate samples also reveal a component within the 400-550 nm range, which is more prominent than the R-PE characteristic emission in the case of the sodium alginate sample. Since for PV applications, the emission of the optically active materials should be mainly in the red/NIR spectral region (matching c-Si maximum absorption, Figure 2a), PVA was selected as the main host matrix in this work. The excitation spectra of C-PC-based samples are  
Figure 3: (**a**) Emission upon excitation at 488, 590, and 410 nm, respectively, and (**b**) absorption spectra of the bio-molecules R-PE, C-PC, and FX in solution. Figure 2: (**a**) Emission spectra for R-PE/PVA, C-PC/PVA, and FX/PVA excited at 498, 575, and 405 nm, respectively. The \(c\)-Si spectral response is shown on the right \(y\)-axis. (**b**) Excitation spectra for R-PE/PVA, C-PC/PVA, and FX/PVA monitored at 720 nm. The shadowed area represents the AM1.5G solar spectrum (right \(y\)-axis). formed by a main C-PC-related component around 620 nm, showing no relevant changes after incorporation into PVA (Figure 2b). The fluorescence decay curves of all samples revealed a single-exponential decay (Figures S9-S11 in Supplementary Materials). The lifetime values of R-PE in H\({}_{2}\)O and R-PE/PVA were similar to that previously reported for the aqueous solution of R-PE [18]. A significant increase in the emission lifetime was found for the R-PE/alginate sample, although lower than that found for R-PE dispersed in gelatin [18]. In this case, such an increase was explained by the dispersion of the molecules in the film, which reduced the number of molecule-molecule non-radiative interactions, concomitantly increasing the lifetime [18; 33]. For the C-PC based samples, the lifetime values found for C-PC in H\({}_{2}\)O were similar to the one recently reported for an aqueous solution of C-PC [5], which was further enhanced when incorporated in the PVA matrix. In the case of FX, the lifetime values showed a slight decrease when incorporated in the PVA, compared to that found for the FX in ethanolic solution (Table S1 in Supplementary Materials). The emission features were further quantified by the measurement of the absolute emission quantum yield (\(\eta\), Table 1 and Table S1 in Supplementary Materials) for excitation wavelength around the excitation maxima. For the samples in solution, the maximum \(\eta\) values obtained for R-PE and C-PC in H\({}_{2}\)O were 0.20 \(\pm\) 0.02 and 0.17 \(\pm\) 0.02, respectively, which are consistent with previously reported values [5; 15]. For the FX in ethanol, the value found was 0.08 \(\pm\) 0.01. After incorporation, the \(\eta\) of the R-PE decreases both for PVA and alginate samples, being the maximum \(\eta\) value measured for the R-PE-based samples (Table 1). Additionally, for the C-PC/PVA, the \(\eta\) is lower when compared to the value found for the aqueous solution (Table 1), suggesting aggregation, as already reported for the incorporation of R-PE in gelatin films [18; 34]. For the case of the FX samples, the \(\eta\) values remain constant (0.08 \(\pm\) 0.01 in solution to 0.10 \(\pm\) 0.01 after incorporation into PVA), likely because FX is a xanthophyll that does not suffer aggregation. To infer the photochemical stability of the solid samples at room temperature, the \(\eta\) values were measured after 6 months of storage at ambient light-exposed conditions. It was found that the values remain similar to the ones measured for the as-prepared samples (Table S2 in Supplementary Materials), thus demonstrating their optical stability. Additionally, prospecting future PV applications, the \(\eta\) values measurements were performed after continuous exposure to AM1.5G irradiation (Figure 4 and Table S2 in Supplementary Materials). The results showed that the most stable sample is the FX/PVA, with a decrease of about 40% of the initial \(\eta\) values after 960 min of exposure.