Composition–structure–luminescence and enhancement of Cr 3+ activated broadband near infrared phosphors for night vision, bio-imaging, and noninvasive detection

In the construction of novel near-infrared (NIR) radiation sources, NIR phosphors equipped with a large emission range and thermally stable luminescence are highly desired. In this work, we designed and prepared a series of Cr 3+ activated and Cr 3+ /Yb 3+ co-activated KScP 2 O 7 (KSPO) phosphors, with their composition–morphology–structure properties and interaction mechanisms systematically investigated. Excited by 475 nm, KSPO:0.03Cr 3+ can emit 700–1200 nm NIR light peaking at 873 nm with a large full width at half maximum (FWHM, 163 nm) corresponding to the 4 T 2 → 4 A 2 transition among Cr 3+ ions. Cr 3+ ions occupy solo crystal sites with a weak local crystal-field environment, which is verified to be responsible for the NIR broadband emission. With the addition of Yb 3+ , extra NIR emission dominating at 968 nm was obtained, as a result of the 2 F 5/2 → 2 F 7/2 transition of Yb 3+ ions. The internal quantum efficiency was improved from 27.3% of KSPO:0.03Cr 3+ to 40.5% of KSPO:0.03Cr 3+ ,0.004Yb 3+ phosphor, mainly benefiting from the energy transfer of Cr 3+ → Yb 3+ . The fabricated NIR pc-LED, utilizing KSPO:0.03Cr 3+ ,0.004Yb 3+ phosphor and a 470 nm LED chip, exhibits high output power (37.56 mW@320 mA). Taking this NIR pc-LED as a radiation source, the doll model, the cleanser content, and high-resolution human hand vein imaging are visualized with the assistance of a NIR camera. The present work suggests that Cr 3+ /Yb 3+ co-activated KSPO phosphor has considerable application prospects in night-vision, bio-imaging, and noninvasive detection.