Transparent Wood Film Incorporating Carbon Dots as Encapsulating Material for White Light-Emitting Diodes
2018
Bi, Zhihao | Li, Tuanwei | Su, Hui | Ni, Yong | Yan, Lifeng
Epoxy resins are the main encapsulation materials for light-emitting diodes (LEDs) due to their high transparency, appropriate mechanical strength, and excellent thermal stability. However, environmentally benign materials needed to be developed with improving performances. Transparent wood and its nanocomposites prepared from natural biomass are potential alternative materials to them. Green preparation of transparent wood incorporating with trichromatic systems is an attractive topic, especially for white LEDs (W-LEDs). Here, multiple-color-emission carbon dots (CDs), serving as trichromatic systems in W-LEDs, were synthesized by tuning the extent of graphitization and surface function of the nanoparticles using citric acid and urea as feedstocks. Then, a green, facile, and energy-efficient method for the preparation of carbon dots/transparent wood (CDs-TW) composites was raised by the ultrafast removing of lignin from wood using deep eutectic solvent (DES, oxalic acid and choline chloride) under microwave-assisted treatment, and then, CDs and poly(acrylic acid) (PAA) were filled into the delignified wood through an in situ polymerization. The transparent wood film embedding multicolor CDs was fabricated, which showed white light emission under ultraviolet light excitation and enhanced mechanical tensile strength (60.92 MPa). Simultaneously, the as-prepared film can be used as an encapsulation film for white LEDs, which exhibited excellent color characteristics with the Commission Internationale Eclairage (CIE) color coordinates, a correlated color temperature (CCT), and a color rendering index (CRI) of (0.33, 0.32), 5237 K, and 83, respectively. This provides a simple route to prepare metal-free wood-based encapsulating materials for W-LEDs.
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