Two-site Cr3+ occupation in the MgTa2O6:Cr3+ phosphor toward broad-band near-infrared emission for vessel visualization

Abstract

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) have great potential in photonic, optoelectronic and biological applications, while the discovery of a broad-band NIR phosphor still remains a challenge. Here, we report a novel Cr³⁺-activated MgTa₂O₆ phosphor with an asymmetrical emission band ranging from 700 to 1150 nm and a large full width at half maximum (FWHM) of 140 nm upon 460 nm blue light excitation. The broad spectrum is assigned to the overlap of two bands centered at 910 and 834 nm, which originate from the spin-allowed transition of ⁴T₂ → ⁴A₂ for different Cr³⁺ ions located in the two six-coordinated crystallographic sites of Mg²⁺ and Ta⁵⁺, respectively. The distribution of blood vessels and bones in human palm and wrist is observed with the assistance of a commercial NIR camera and a fabricated pc-LED, which demonstrates that the MgTa₂O₆:Cr³⁺ phosphor is promising in biological applications.