Photoluminescent and photochromic smart window from recycled polyester reinforced with cellulose nanocrystals.

Smart windows with long-persistent phosphorescence, ultraviolet (UV) light protection, high transparency, and high rigidity were developed by easily immobilizing varying ratios of lanthanide-activated aluminate phosphor nanoscale particles within a composite of recycled polyester/cellulose nanocrystals (RPET/CNC). Cellulose nanocrystals were prepared from rice straw waste. Cellulose nanocrystals were used at low concentration as both crosslinker and drier to improve both transparency and hardness. The phosphor nanoscale particles must be distributed into the recycled polyester/cellulose nanocrystals composite bulk without agglomeration to produce transparent RPET/CNC substrates. Photoluminescence characteristics were also studied using spectroscopic profiles of excitation/emission and decay/lifetime. The hardness efficiency was also examined. This transparent recycled polyester waste/cellulose nanocrystals nanocomposite smart window has been shown to change colour under UV light to strong green and to greenish-yellow when it is dark, as proved by Commission Internationale de l'éclairage (CIE) laboratory colour parameters. It was found that the afterglow RPET/CNC smart window had phosphorescence intensities of 428, 493, and 523 nm upon excitation at 368 nm. There was evidence of improved UV shielding, photostability, and hydrophobic activity. In the presence of a low phosphor ratio, the luminescent RPET/CNC substrates showed quick and reversible fluorescence photochromic activity when exposed to UV radiation.