###### Abstract  
In the search for a better and brighter future, the use of natural luminescent renewable materials as substitutes for synthetic ones in the energy field is of prime importance. The incorporation of natural pigments (e.g., xanthophylls and phycobiliproteins) is a fundamental step in a broad spectrum of applications that are presently marred by their limited stability. The incorporation of bio-based luminescent molecules into solid matrices allows the fabrication of thin films, which may dramatically increase the range of applications, including sustainable photovoltaic systems, such as luminescent solar concentrators or downshifting layers. In this work, we incorporated R-phycoerythhrin (R-PE), C-phycocyanin (C-PC), and fucoxanthin (FX) into poly(vinyl alcohol) (PVA) and studied their optical properties. It was found that the emission and excitation spectra of the phycobiliproteins and FX were not modified by incorporation into the PVA matrix. Moreover, in the case of FX, the emission quantum yield (\(\eta\)) values also remained unaltered after incorporation, showing the suitability of the PVA as a host matrix. A preliminary photostability study was performed by exposing the solid samples to continuous AM1.5G solar radiation, which evidenced the potential of these materials for future photovoltaics. luminescence; luminescent solar concentrators; luminescent downshifting layers natural pigments; polymer; xanthophyll; phycobiliprotein +
Footnote †: journal: Applied Sciences  
class of biomolecules [5] able to open new perspectives in the field of building-integrated PVs [1; 6], through LSCs [1; 7; 8; 9; 10; 11]. Benefiting from their high absorption coefficient and emission quantum yields, the LSCs are planar waveguides that collect sunlight at the surface and concentrate it into the low area of the edges, where PV cells are applied. The light conversion is mediated by a down-shifting mechanism of the solar radiation, whose performance under diffuse light conditions is an advantage [1; 12]. Examples of bio-based LSCs include the use of phycobiliproteins [13; 14; 15], chlorophyll [16], green fluorescent protein (GFP) [5; 17], and C-phycocyanin (C-PC) [5] with competitive performance compared to those based on synthetic dyes [6]. In these cases, the bio-molecules are used mainly in solution to preserve their intrinsic chemical stability. To enlarge the application range and the processing, the incorporation into solid matrices is a relevant step that has been challenging, as optical performance decreases induced by aggregation [18]. In parallel with performance, challenges for bio-luminescent materials also include the emission red-shift towards the red/NIR spectral region, in resonance with the Si-based PV cells absorption. To incorporate luminescent natural molecules into solid matrices and retain the optical properties/long-term viability, the following issues should be considered: (i) the microenvironment of solid hosts should be similar to or mimic the native environment of the molecules, while simultaneously providing a rigid structure, (ii) the entrapment process should be performed at room temperature, (iii) the bio-molecules usually require neutral solutions, acidic and basic environments should be avoided, and (iv) effects of solvents and ionic strength of the solution should be considered [19]. In this context, several attempts have been done, namely by investigating the use of encapsulation strategies such as sol-gel derived SiO\({}_{2}\) material from tetramethylasilane [20], and hybrid matrices [21] using polymer additives dispersed into sol-gel processed materials derived from tetraethyl orthosilicate alone or copolymerized with methyltriethoxysilane or dimethyldimethoxysilane [21]. [PERSON] and co-authors encapsulated different phycobiliproteins (R-phycoerythrin; R-PE, C-PC, and allophycocyanin; APC) in sol-gel glasses and discovered that the impact on the spectroscopic properties was significantly distinct.