Broadband short-wave infrared Mg4Nb2O9:Cr3+,Li+ phosphor for nondestructive safety detection and biomedical imaging

Abstract

Broadband short-wave infrared (IR) phosphor-converted light-emitting diodes (pc-LEDs) are deemed as excellent light sources for miniature near-IR (NIR) spectroscopy but suffer from a lack of efficient phosphors with emission peaks >850 nm. Novel solid solution Mg₄Nb_xTa_2−xO₉: 3%Cr³⁺ phosphors were developed for efficient Cr³⁺: ⁴T₂(4F) → ⁴A₂ transition at 920 nm with a large full-width at half-maximum of ∼164 nm. Benefiting from the synergistic effects of particle growth, higher crystallinity, and Li⁺ compensation, the NIR emission intensity of Cr³⁺ continuously increased with increasing Nb component and even reached twice the value for optimized Mg₄Nb₂O₉: 3%Cr³⁺,Li⁺. The optimized sample featured a substantial internal quantum efficiency (QE) of ∼67.1% and an external QE of ∼26.1%. By combing a blue LED chip of ∼465 nm with the optimized phosphor, a self-built pc-LED was tested to exhibit relatively advanced performance, i.e., NIR output powers of 5.1 mW at 20 mA and 62.4 mW at 320 mA as well as a photoelectric efficiency of 10.3% at 20 mA. The broadband NIR pc-LED was successfully applied to clearly image objects behind a plastic cover and to recognize blood vessel distribution inside a human finger and fist. Further development of such Cr³⁺-activated phosphors (pc-LEDs) will greatly advance the technology of nondestructive safety detection and biomedical imaging, among others.