Abstract
Carbon quantum dots (CQDs) were manufactured from citric acid and urea in a gram-scale synthesis with a controlled size range between 1. 5 and 23.8 nm. The size control was realized by varying volume of the precursor solution in a hydrothermal synthesis method. The prepared CQDs were investigated using electrochemiluminescence (ECL) spectroscopy at interfaces of their electrode films and electrolyte solution containing coreactants rather than conventional optoelectronic tests, providing an in-depth analysis of light-emission mechanisms of the so-called half-cells. ECL from the CQD films with TPrA and K2S2O8 as coreactants provided information on the stability of the CQD radicals in the films. It was discovered that CQD•− has a powerful electron donating nature to sulfate radical to generate ECL at a relative efficiency of 96% to the Ru(bpy)3Cl2/K2S2O8 coreactant system, indicating a strong performance in light emitting applications. The smaller the CQD particle sizes, the higher the ECL efficiency of the film interface, most likely due to the increased presence of surface states per mass of CQDs. Spooling ECL spectroscopy of the system revealed a potential-dependent light emission starting from a deep red color to blue-shifted intensity maximum, cool bright white emission with a correlated color temperature of 3,200 K. This color temperature is appropriate for most indoor lighting applications. The above ECL results provide information on the performance of CQD light emitters in films, permitting preliminary screening for light emitting candidates in optoelectronic applications. This screening has revealed CQD films as a powerful and cost-effective light emitting layer toward lighting devices for indoor applications.
Highlights
Light emitting diodes (LEDs) have been at the forefront of lighting technology recently due to their decreased energy consumption over compact fluorescent and incandescent lighting technologies
A protocol to prepare Carbon quantum dots (CQDs) with controlled size was created from cost effective and readily available precursors
As a CQD film, the smallest CQDs had strong white light emission when reacted with 50 mM of the coreactant S2O82−
Summary
Light emitting diodes (LEDs) have been at the forefront of lighting technology recently due to their decreased energy consumption over compact fluorescent and incandescent lighting technologies. LEDs are conventionally created by depositing many subsequent layers on a substrate in an inert atmosphere (Zhang et al, 2013; Gao, 2018; Kusamoto and Nishihara, 2018; Yang et al, 2019). White ECL of CQD Films reduce manufacturing costs and operating voltages. To this end, light emitting electrochemical cells (LECs or LEECs) have gained interest. LECs conventionally comprise of two electrodes sandwiching a light-emitting layer that is responsible for both charge transport and light emission (Fresta and Costa, 2017). The polymer electrolyte reduces bulk and contact resistance over LEDs, allowing for air-stable and thicker electrodes. The reduced potentials and simpler device structure allow for cost-effective manufacturing of energy efficient lighting sources
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