Spectrally tunable and thermally stable near-infrared luminescence in Na3Sc2(PO4)3:Cr3+ phosphors by Ga3+ co-doping for light-emitting diodes

Abstract

Near-infrared (NIR) phosphor-converted light-emitting diodes (LEDs) are becoming an efficient and promising solution for high-power NIR light sources, which have shown a broad range of possible applications in the fields of agriculture, food analysis and biomedical diagnostics. However, there is a long-standing challenge to develop tunable and thermally stable NIR-emitting phosphors as luminescence converters in the design of low-cost, compact and high-efficiency NIR LEDs. Here, we report a tunable broadband NIR photoluminescence in Na₃Sc₂(PO₄)₃:Cr³⁺ phosphors via Ga³⁺ co-doping and explore their application in NIR LEDs. With the fine-tuning of the doping concentration of Ga³⁺ ions from 0 to 6%, the NIR luminescence of the obtained phosphor can be tuned from sharp line emission at 694 nm (²E → ⁴A₂ transition of Cr³⁺) to broadband emission centered at 750 nm (⁴T₂ → ⁴A₂ transition of Cr³⁺) upon blue light excitation. In the meanwhile, the NIR emission intensity at 100 °C and 150 °C can retain ∼100% and ∼84% of the initial value at room temperature when the Ga³⁺ content is determined to be 6%, leading to thermally stable broadband NIR emission in the as-synthesized Na₃Sc₂(PO₄)₃:Cr³⁺,Ga³⁺ phosphors. The NIR LEDs constructed by combining the commercial blue LED chips with the optimized NIR phosphors can generate broadband emission in the wavelength range of 600–1000 nm and deliver ∼4 mW of NIR output power with a power conversion efficiency of 2.6% at a drive current of 60 mA. The potential of the fabricated NIR LEDs as a lighting source for night vision and vein imaging is also demonstrated. The outcomes here highlight promising potential for Na₃Sc₂(PO₄)₃:Cr³⁺,Ga³⁺ as phosphor-downconverted light emitters in the design of high-power NIR LED devices for practical applications.