According to a report by Sun Danning from China Science Daily, Professor Tian Ying's team at Dalian Maritime University has recently made new progress in the field of high-efficiency near-infrared light sources pumped by blue LEDs. By designing the cation and crystal structure in the sulfide, NaLaS2:Yb3+ phosphor achieves absorption coverage of the entire blue light region, matching the emission position of commercial blue LED chips. The relevant results were published in Laser & Photonics Reviews.

Near-infrared light has important applications in fields such as biological imaging, non-destructive testing, and night vision. Due to its unique advantages, such as deep penetration, non-injury, and invisibility, it plays a crucial role. However, the development of traditional near-infrared light sources faces severe challenges due to their large size, low efficiency, and high cost. Phosphor-converted LED (pc-LED) technology is regarded as an ideal alternative, with the core being the development of efficient near-infrared phosphors excited by blue light. Currently, commercially available blue LEDs can effectively excite near-infrared phosphors mainly relying on the mixing of Cr3+ ions.

However, the d-d transition of Cr3+ ions is partially forbidden, resulting in low photon absorption efficiency. In contrast, charge transfer states (CTS) belong to allowed transitions and can achieve strong absorption. However, most charge transfer absorption sites are located in the ultraviolet region. Therefore, the key to promoting the development of a new generation of efficient near-infrared light source technology is to shift the CTS energy levels to the blue region and construct a new blue light sensitization mechanism.

In this work, the team successfully adjusted the absorption band of S2-→Yb3+ CTS to shift towards lower energy. When stimulated by 450nm light, NaLaS22 exhibits strong Yb3+ emission at 9944 nm near-infrared wavelength, with internal and external quantum efficiencies reaching up to 64% and 45%, respectively. This phosphor also demonstrates excellent thermal stability, maintaining an emission intensity of 88.7% at room temperature even below 420K. Based on NaLaS2:Yb3+ phosphor, near-infrared pc-LEDs fabricated exhibit superior photoelectric conversion efficiency and near-infrared output power in fields such as non-destructive testing, biological imaging, and night vision.

This work provides a new strategy for developing high-efficiency solid-state light sources pumped by blue LEDs. (Source: China Science Daily, Author: Sun Danning)