Sínteses e caracterização de carbon dots para atuarem como conversor de luz em diodos emissores de luz

Abstract

Light-emitting diodes (LEDs) have revolutionized modern lighting due to their high luminous efficiency and lower environmental impact. However, traditional LEDs rely on rare earth ions, which are costly and non-renewable resources. In recent years, Carbon Dots (CDs) have emerged as new luminescent materials to make LEDs free from rare earth elements, thanks to their properties such as excellent photo-stability, simple and cost-effective synthesis, biocompatibility, low toxicity, as well as high quantum efficiency and broad absorption, excitation, and emission spectra. In this study, CDs were synthesized from Neutral Red dye with citric acid (Nr-CDs) to generate a fluorescent film and apply it as a light converter in LEDs. The Nr-CDs were incorporated into the PVA (Polyvinyl Alcohol) polymer to obtain the fluorescent film (Nr-CDs-F). High-Resolution Transmission Electron Microscopy (HRTEM) indicated that Nr-CDs have a well-defined graphitic structure and an average size distribution of 3.74 ± 0.63 nm. Furthermore, Fourier Transform Infrared Spectroscopy (FTIR) revealed the presence of oxygenated (C=O, C-O) and nitrogenated (N-H, C-N) groups on the surface of Nr-CDs. UV-VIS spectroscopy showed absorption bands related to π - π* and n - π* transitions, corresponding to the graphitic structure and functional groups on the surface of Nr-CDs, respectively. Due to these different groups, Nr-CDs exhibited dual emission behavior centered at 450 nm (excitation-dependent) and 600 nm (excitationindependent). By varying λExc, Nr-CDs displayed different emissions near the CIE color coordinates (x,y) of pure white light (0.33, 0.33). The film containing the nanoparticle (NrCDs-F) retained the optical properties of the aqueous Nr-CDs, presenting CIE color coordinates for all types of whites (Cool, Warm, and Neutral). Additionally, Nr-CDs-F exhibited excellent Color Rendering Index (CRI) values ranging from 80 to 84 and, when applied as a light converter in commercial UV LED (λexc= 200 nm, 50 cd.m-2), enhanced its efficiency by approximately 2 times (109 cd.m-2). Moreover, different CIE color coordinates were obtained by varying the current (3.5 to 7.5 eV) of the LED. In conclusion, the results indicate that Nr-CDs-F produced by modulating the fluorescence of CDs was efficient for light conversion and increased the efficiency of the commercial LED.