Adjusting optical and fluorescent properties of quantum dots: moving towards best optical heat-rejecting materials

Quantum dots (QDs) coatings have recently attracted attentions as novel nano-scale fluorescent cooling materials with adjustable thermo-optical properties for urban overheating mitigation application. In this paper, a mathematical method for the prediction of impact of optical and fluorescent properties (i.e. absorption edge wavelength (λ_AE) and quantum yield (QY)) on fluorescent cooling indicators including re-emitted energy (Q_PL), effective solar reflection (ESR), and PL-related surface temperature reduction was proposed. The experimental thermal evaluation testing on three PbS QDs sample with different fluorescent properties and their corresponding non-fluorescent samples was performed to assess the accuracy of the proposed predictive model and evaluate the impact of fluorescent/optical properties on their cooling potential. The validated model was then used to optimize the fluorescent cooling potential for QDs samples with different fluorescent/optical properties. According to the model results, surface temperature reduction potential through PL effect demonstrates its highest value for QDs with solar absorption and QY near to unity, and λ_AE at around 1300 nm. QDs coatings with the optimal solar absorption, QY, and λ_AE showed up to 35 °C lower surface temperature than their corresponding non-fluorescent reference sample in a typical sunny day in Sydney. The maximum fluorescence contribution (Effective solar reflection (ESR)- Solar reflection (R)) is also estimated to be 0.44 for the fluorescent material with optimal optical and fluorescent property. Results of this study will support the next phase of research on fluorescent cooling.