One-Step Extrusion Preparation for Low-Cost Multicolored Carbon Dot Fluorescent Films.

Carbon dots (CDs), an emerging class of environmentally friendly luminescent materials, have been extensively applied in full-color display of light-emitting diodes (LEDs). However, the synthesis of CDs usually requires high pressure, and the conventional preparation of CD-based LED films involves intricate manufacturing techniques. The resulting security risk and high cost restrict the further application of CD-based LEDs. Here, we present a cost-effective method to obtain CD-based LED films via in situ extrusion in a twin-screw extruder. By fine-tuning the extrusion temperature, we created blue-emitting LEDs. The resulting fluorescent films exhibited remarkable stability, retaining 94% fluorescence intensity after 180 days of storage. We also prepared yellow, pure white, and cool white LEDs with malleable shapes, validating the versatility of the in situ extrusion method. More importantly, the manufacturing cost for CD-based films amounts to only about 0.8 RMB/g, which is substantially lower than that of the reported preparation methods. This work offers a cost-effective, safe, and massive approach to preparing photoluminescent LEDs, paving the way for the development of more sustainable and efficient CD-based LEDs.

Bright Blue Emission Lead-Free Halides with Narrow Bandwidth Enabled by Oversaturated Europium Doping.

Eu2+-based lead-free metal halide nanocrystals (LFMH NCs), including CsEuCl3 NCs and CsX:Eu2+ NCs (X = Cl or Br), exhibit highly efficient narrow-band blue photoluminescence, making them competitive candidates for next-generation lighting and displays. However, the growing mechanism of the aforementioned NCs lacks in-depth study, which hinders the development of Eu2+-based nanomaterials. Herein, we demonstrate the colloidal synthesis of CsBr:Eu2+ NCs based on an air-stable europium source. The NCs show deep blue photoluminescence centered at 444 nm, with a maximum photoluminescence quantum yield (PLQY) reaching 53.4% and a fwhm of 30 nm. We further reveal the mechanism that determines CsBr host growth and Eu2+ doping in CsBr:Eu2+ nanocrystals, especially dopant trapping and self-purification, that determine the PLQY level. Pure white, warm white, and cold white LEDs are fabricated based on CsBr:Eu2+ NCs, red and green phosphors, and their performance suits the needs of high-quality lighting.