Regulation of Brightness Attributes of High-Stability Carbon Quantum Dots Applicable in LED Digital Color Display.

Fluorescent carbon dots (CDs) attract much attention due to high stability and low toxicity. For high brightness, multi-color emission and fluorescence stability, polystyrene (PS)/CDs composite films were prepared. First, three types of CDs and three PS/CDs films were prepared. Then, three light-emitting-diode (LED) devices were achieved. Compared to CDs solutions, CDs filled films show almost unchanged photoluminescence (PL) spectra. PL peaks of blue, green and red films appear at 462 nm, 544 nm and 603 nm, separately. Blue CDs lead to highest photoluminescence quantum yields (PLQYs) of 76% (solution) and 49% (film). A certain level of thermal stability and fluorescent reversibility of blue film were verified. After 60 days of air exposure, PL intensities of blue and green films reach 97% and 93% of original values, separately. Improving work time cannot vary PL wavelengths of devices. For blue-emitted device, PL intensity reaches 55% of original value after working for 600 min. For green-emitted device, PL intensity reaches 80% after working for 300 min. The novelty is effective PS encapsulation and uniform dispersion of CDs to yield favorable fluorescence properties of devices. This work inspires ideas for large-scale preparation of fluorescent films for LED digital color display.