Near-infrared (NIR, 700-2500 nm) microlight-emitting diodes (micro-LEDs) are gaining attention for their potential in applications like biosensing, virtual reality/augmented reality (VR/AR), remote sensing, and optical communication. However, traditional NIR phosphors have limitations, including large particle size, low emission efficiency, poor stability, and the presence of toxic heavy metals (Cd²⁺ and Pb²⁺), which restrict their use in micro-LED technology. Therefore, the development of non-toxic, high-efficiency near-infrared nanophosphors is of great importance. To learn more about Micro LED technology advancements, check out this comprehensive article.
Recently, a team led by Researcher Da-Tao Tu and Professor Xue-Yuan Chen from the Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, and the Mindu Innovation Laboratory, has made a significant breakthrough. They developed high-efficiency NIR quantum dot phosphors based on CuInSe₂²⁺ (CISe²⁺) and applied them to micro-LEDs for the first time. This project received support from key projects of the National Natural Science Foundation of China and regional innovation development joint funds.
Innovations in Near-Infrared Quantum Dot Phosphors
The team successfully achieved a broad emission peak range from 750 nm to 1150 nm by precisely tuning the Cu/In and Zn/In ratios in CISe²⁺ nanocrystals. Coating the material with a ZnSe shell significantly improved its stability and emission efficiency, resulting in an absolute NIR quantum yield of 92.8%. They then fabricated light-converting mini-LEDs, optimizing conditions to ensure uniform dispersion of quantum dots in the encapsulation resin, which prevented fluorescence quenching caused by aggregation. The device achieved a NIR irradiation flux of 88.7 mW at 350 mA, the highest reported value for non-toxic NIR quantum dot light-converting LEDs. It also demonstrated remarkable stability, maintaining 94.5% of its original emission efficiency after 72 hours under dual 85 aging conditions (85°C and 85% humidity) and retaining 98.2% of its emission efficiency after 10 cycles of temperature changes between 25°C and 150°C.
Application in Micro LEDs Using Advanced Printing Technology
In collaboration with Fuzhou University, the team applied CISe²⁺@ZnSe phosphors to NIR micro-LEDs using electrohydrodynamic printing technology. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed that the micro-light arrays produced had regular shapes and adjustable sizes, with no coffee rings or tailing phenomena. When the blue light chip was activated, the arrays emitted a strong NIR signal, with the smallest pixel diameter reaching 3.7 µm—far superior to current commercial inkjet printing technologies (10-30 µm). Leveraging these advanced quantum dot phosphors, the team successfully printed a 10 × 10 mm pattern, showcasing excellent reproducibility and stability. This achievement opens new avenues for the development of high-efficiency NIR nanophosphors in micro-LEDs, paving the way for advancements in NIR micro-nano devices and flexible electronics. The findings have been published in Advanced Materials under the title “Near-Infrared Nanophosphors Based on CuInSe₂ Quantum Dots with Near-Unity Photoluminescence Quantum Yield for Micro-LEDs Applications” (DOI: 10.1002/adma.202311011).
Previous Achievements in Near-Infrared Materials
Professor Chen’s team has previously made notable strides in designing, synthesizing, and applying NIR fluorescent materials. Their achievements include developing high-efficiency second NIR (NIR-II) quantum dot probes based on CuInSe₂ for circulating tumor cell detection and real-time tumor-targeted imaging (Nano Today 2020, 35, 100943). They have also enabled efficient NIR emission of rare-earth ions in a Cs₂NaInCl₆ matrix using a charge transfer sensitization strategy (Adv. Sci. 2022, 9, 2203735), and developed Cs₂(Na/Ag)BiCl₆³⁺, Er³⁺ NIR phosphors through local symmetry regulation for NIR imaging (Angew. Chem. Int. Ed. 2022, 61, e202205276). More recently, they used trap-controlled strategies to develop Cs₂NaGdF₆ phosphors doped with rare-earth ions, achieving tunable afterglow properties.
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