Unlocking non-characteristic near-infrared emission of rare earth ions for photosynthetic bacteria cultivation and vein imaging applications†

Near-infrared (NIR) luminescent materials exhibit unique photophysical properties that make them crucial components in photobiological, photonic and optoelectronic applications. Nonetheless, almost all rare earth ions are difficult to be efficiently excited by blue light for NIR emission, mainly due to the inherent electron shielding effect of 5s²5p⁶ orbitals. Here, an amazing enhancement of the Tm^{3+ 3}H₄ → ³H₆ transition (800 nm) was achieved in the SrGa₁₂O₁₉ host upon 450 nm excitation. Compared with the Tm³⁺ single-doped sample, the internal quantum efficiency (IQE) in the 700–900 nm range was significantly improved from less than 1% to 74%, and the external quantum efficiency (EQE) was enhanced from nearly 0 to 33%, benefitting from the synergistic effect of Cr³⁺ contribution and electron shielding effect breaker of In³⁺. XRD structure refinement, time-resolved fluorescence spectroscopy and electron paramagnetic resonance were used to determine the effect of Cr³⁺ and In³⁺ doping. Furthermore, the universality of this strategy has also been verified with other rare earth ions (Ho³⁺, Nd³⁺, and Yb³⁺). Finally, a NIR phosphor-converted LED (pc-LED) is fabricated, exhibiting a satisfactory output power of 141 mW@500 mA and demonstrating the potential for photosynthetic bacteria culture, venous imaging and non-destructive testing. This work opens a window for blue light-pumped NIR emission of rare earth ions.