Or first for MicroLEDs! Fujian Institute of Paper Formosa develops efficient near-infrared quantum d

Near-infrared luminescent (NIR, 700-2500 nm) micro diodes (Micro LEDs) have important application value in fields such as biosensing, virtual reality/augmented reality (VR/AR), remote sensing and optical communications. Traditional near-infrared phosphors have problems such as large particle size, low luminescent efficiency, poor luminescent stability or containing heavy metal toxic elements (Cd2 + and Pb2 +), which greatly limits their application in the field of Micro LEDs. Therefore, it is of great significance to develop a class of non-toxic and efficient near-infrared nano-phosphors.

Recently, Researcher Tu Datao and Chen Xueyuan's team of Fujian Institute of Material Structure/Mindu Innovation Laboratory of China Academy of Sciences successfully developed CuInSe2: Zn2 +(CISe: Zn2 +)-based high-efficiency near-infrared quantum dot phosphors with the support of key projects of the National Natural Science Foundation of China and the Regional Innovation and Development Joint Fund, and applied it to Micro LEDs for the first time (Figure 1).

Figure 1. Schematic diagram of efficient CISe: Zn2 +@ZnSe near-infrared quantum dot phosphor and its Micro LED application

By accurately designing the Cu/In and Zn/In composition ratios in CISe: Zn2 + nanocrystals, the research team achieved a wide range of control of the emission peak from 750 nm to 1150 nm; after coating the ZnSe shell, the stability of the material and Luminous efficiency have been significantly improved, and the absolute quantum yield in the near infrared reaches 92.8%.

Based on this, the team prepared a light-conversion mini-LED. By optimizing the experimental conditions, the uniform dispersion of quantum dots in the encapsulation compound was achieved, effectively avoiding the problem of aggregation fluorescence quenching. The near-infrared irradiation flux was as high as 88.7mW@350mA, which is currently the highest value reported for non-toxic near-infrared quantum dot light-conversion LEDs.

At the same time, the device showed excellent stability: after 72 hours of dual 85 aging (85 ° C and 85% humidity), it could maintain a luminous efficiency of 94.5%; after 10 cycles of temperature change at 25-150 ° C, it could still maintain the initial luminous efficiency of 98.2%.

Further, the team cooperated with Fuzhou University to use electrofluidic printing technology to apply CISe: Zn2 +@ZnSe phosphor to near-infrared Micro LEDs. It was confirmed by scanning electron microscopy and atomic force microscopy that the prepared micro-luminescent array has regular shape, adjustable size, and no phenomena such as coffee rings and tailing; in particular, after the blue light chip is lit up, the array emits a strong near-infrared light signal, and the minimum diameter of the luminescent pixel point is 3.7 m, which is far better than the current commercial inkjet printing level (10-30 m).

Based on the excellent performance of the quantum dot phosphor, the team spray printed a pattern of 10 - 10 mm, and the locally enlarged array showed good repeatability and stability (Figure 2). This work provides new ideas for the development of efficient near-infrared nano-phosphors and their Micro LED applications, and also lays a good foundation for the development of near-infrared micro-nano devices and flexible electronic devices.

Relevant results were published online in full text in Advanced Materials (Adv. Mater. 2024, 36, 2311011). The first author of the paper is Lian Wei, a doctoral candidate at the Fujian Institute of Materials Research, China Academy of Sciences/Fuzhou University Joint Training. The corresponding authors are Researcher Tu Datao, Researcher Zhu Haomiao and Researcher Chen Xueyuan of the Fujian Institute of Materials Research, China Academy of Sciences/Mindu Innovation Laboratory, and Associate Professor Yang Kaiyu of Fuzhou University.

Figure 2.(a) Schematic diagram of preparing Micro LEDs. (b-c) scanning electron microscope image,(d-e) near-infrared fluorescence image and (f-i) atomic force microscope image of the Micro LED array. (j) fluorescent pattern and (k-m) local magnified fluorescent image based on Micro LED array spray printing

Previously, Chen Xueyuan's team has made a series of important progress in the design, synthesis and application of near-infrared fluorescent materials. For example, a CuInSe2-based high-efficiency near-infrared two-region luminescent quantum dot biological probe was developed and applied to circulating tumor cell detection and tumor-targeted real-time imaging.(Nano Today2020,35, 100943); Using a charge-transfer transition sensitization strategy, efficient near-infrared luminescence of rare earth ions in a Cs2NaInCl6 host was achieved (Adv. Sci. 2022, 9, 2203735); Through local symmetry control, a Cs2(Na/Ag) BiCl6: Yb3 +, Er3 + near-infrared phosphor was developed and applied to near-infrared imaging (Angew. Chem. Int. Ed. 2022, 61, e202205276); Using trap control strategies, a long-lasting and photostimulated rare earth doped Cs2NaGdF6 phosphor with tunable UV-visible-near infrared full spectrum has been developed (Matter2023,6, 4261).