Development of high-performance NIR-to-SWIR down-shifting Li₃Ba₂Gd₃(MoO₄)₈:Yb³⁺/Tm³⁺ and Yb³⁺/Ho³⁺ for phosphor...

High-performance short-wave infrared (SWIR) phosphors are of increasing interest for phosphor-converted light-emitting diodes (pc-LEDs) used in sensing, imaging, and analytical applications. In this work, Li₃Ba₂Gd₃(MoO₄)₈ (LBGMO) phosphors co-doped with Yb³⁺/Tm³⁺ and Yb³⁺/Ho³⁺ were developed as efficient near-infrared (NIR)-to-SWIR down-shifting (DS) materials. Phase purity and crystal structure were confirmed by X-ray diffraction, demonstrating successful incorporation of rare-earth ions into the LBGMO host lattice. Under 940 nm excitation, efficient sensitization by Yb³⁺ ions enables strong SWIR emission from both activator ions. The Yb³⁺/Tm³⁺ system exhibits broadband emission centered at approximately 1800 nm, originating from the Tm³⁺: ³F₄ → ³H₆ transition, whereas the Yb³⁺/Ho³⁺ system shows dominant emission near 2050 nm associated with the Ho³⁺: ⁵I₇ → ⁵I₈ transition. High photoluminescence quantum yields (PLQY) of 63% and 69% were achieved for the Yb³⁺/Tm³⁺ and Yb³⁺/Ho³⁺ phosphors, respectively, accompanied by efficient energy transfer from Yb³⁺ to Tm³⁺ (95%) and Ho³⁺ (96%). The moderate cut-off phonon energy of 930 cm^-1 supports efficient population of the lower-energy SWIR-emitting states, while the rate of non-radiative relaxation remains sufficiently low to prevent effective competition with radiative transitions. Phosphor-converted LED devices using 940 nm excitation and fabricated with the developed phosphor conversion layers exhibited maximum wall-plug efficiencies of 1.6% for Yb³⁺/Tm³⁺ and 3.6% for Yb³⁺/Ho³⁺. Demonstration of SWIR imaging through visibly opaque materials and spectral overlap with water absorption bands confirms the potential application of these materials.