Exploring the potential of photoluminescence for urban passive cooling and lighting applications: A new approach towards materials’ optimization

Different passive strategies are investigated with the aim of reducing the overwhelming problem of energy consumption and greenhouse gases emissions in the built environment. A careful selection of the urban skin can mitigate the Urban Heat Island (UHI) phenomenon and, consequently, improve comfort conditions in indoors and outdoors, and reduce the ever-increasing energy consumption. In this context, the present study aims at investigating innovative cool materials with photoluminescent properties that may be exploited to increase energy saving thanks to the provided cost-free lighting contribution. A new methodology for the analysis of their thermo-optical and photometric behavior is proposed, combining existing techniques dedicated to both photoluminescence and traditional building materials. The luminous samples' performance is experimentally evaluated during both their charging and discharging phase. Furthermore, analyses of covariance are carried out in order to quantitatively assess the impact of samples’ composition on their luminous and optical performances. Results demonstrate how the latter are mainly influenced by the time of excitation and the mixture of chemical compounds, and testify their promising potential as cool materials for UHI mitigation and energy saving strategy. Both these outcomes pave the way for exploiting and scaling up the potential of photoluminescence in highly reflective urban skins, with the ability to emit light as reliable passive lighting sources.