Abstract
To mitigate solar heating in colored objects, fluorescent coloration has been proposed as an alternative to traditional absorptive pigments. However, the Stokes-shifted photons generated by fluorophores predominantly remain trapped by total internal reflection (TIR), increasing the parasitic solar absorption and the radiative thermal load. This work introduces a scattering-enhanced light extraction strategy that overcomes the TIR limit in fluorescent films. A sequential quadratic programming-driven optimization model establishes the theoretical minimum radiative thermal load for both traditional and fluorescent-colored surfaces. Results reveal that while traditional absorption-based color achieves only 19.3% sub-ambient cooling chromaticity in the CIE 1931 color space, light extraction technology expands the range from 26.7% to 64.9% for fluorescent color. TiO(2) nanoparticles enhance light extraction through multiple Mie-scattering, with Monte Carlo ray-tracing simulation identifying an optimal 0.5 wt% TiO(2) nanoparticle concentration yielding 85.9% light extraction efficiency, significantly outperforming the TiO(2)-free fluorescent film (25.3%) and a higher 15 wt.% concentration (66.6%). Outdoor experiments confirm the optimal 0.5 wt% sample exhibits a 4.1 °C temperature decrease compared to the control (0 wt.%) sample. This approach offers cost-effective scalability advantages over microtexture-based light extraction methods.