Broadband and High Efficiency Near-Infrared Emission in Cr³⁺-Doped ZnWO₄ Phosphors for Spectroscopic Applications

The increasing demand for near-infrared phosphor-converted LEDs (NIR pc-LEDs) has spurred extensive research on broadband NIR phosphors. A series of Cr³⁺-doped ZnWO₄ phosphors exhibiting broadband NIR emission was synthesized via a high-temperature solid-phase method. The photoluminescence (PL) excitation (PLE) spectrum of ZnWO₄: Cr³⁺ exhibits two absorption bands in the 200-400 nm and 400-600 nm ranges, which match well with near-ultraviolet and blue LED chips. Under excitation, the PL spectrum shows a broad NIR emission extending from 700 to 1400 nm, with a full width at half maximum (FWHM) of approximately 210 nm. The internal quantum efficiency (IQE) was measured to be 55.36%. At 373 K, the integrated emission intensity of ZnWO₄: 0.05Cr³⁺ is about 47.5% of that at room temperature (RT). Additionally, a prototype NIR pc-LED device was fabricated by embedding the ZnWO₄: 0.05Cr³⁺ phosphor into a silicone matrix and coupling it with a 450-nm blue LED chip. The device delivered an output power of 17.12 mW at a 140-mA driving current and a photoelectric conversion efficiency of 14.42% at 20 mA. These results demonstrate the promising potential of this NIR pc-LED for practical applications such as night vision and vein imaging.