Highly efficient and thermally stable broadband NIR phosphors by rationally bridging Cr3+–Yb3+ in LiScGe2O6 for optical bioimaging

Abstract

Broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are considered the most desirable next-generation light sources applied to NIR spectroscopy technology. However, the development of broadband NIR phosphors with high luminescence efficiency, great thermal stability, and emission wavelength exceeding 830 nm is an enormous challenge. Here, a broadband NIR phosphor covering the 750–1200 nm region with a full width at half maximum of 205 nm is designed via the energy transfer (ET) of Cr³⁺ → Yb³⁺ in the alkali-scandium-germanate. The efficient ET not only enriches the longer-wavelength emission within 950–1100 nm but also significantly improves the integrated luminescence efficiency and thermal stability in contrast with the Cr³⁺ singly-doped one. The champion NIR phosphor shows an internal/external quantum efficiency of 76.3%/36.2%, and its emission intensity at 100 °C maintains 86% of the initial intensity. The fabricated NIR pc-LED, using an as-prepared phosphor and a 460 nm LED chip, shows an output power of 22.19 mW@100 mA (64.26 mW@400 mA) and a photoelectric conversion efficiency of 8.22%@100 mA (5.32%@400 mA). Visualization of blood vessel distribution in the human hand was realized using fabricated NIR pc-LED as a radiation source, demonstrating its application prospect in optical bioimaging. This work demonstrates that the ET of Cr³⁺ → Yb³⁺ is an effective strategy to improve luminescence performance, which can stimulate further studies to explore high-performance longer-wavelength NIR phosphors in the future.