Simultaneously strong NIR-II and NIR-III luminescence induced by Cr3+-Yb3+-Er3+ energy transfer in KScP2O7 for NIR thermometry, NIR pc-LED and night-vision applications

The luminescence in NIR-II and NIR-III ranges has high penetration, as well as lower scattering and absorption in biological tissues. It is crucial to develop phosphors with strong emissions covering both spectral ranges. A novel Cr3+-Yb3+-Er3+ activated KScP2O7 phosphate phosphor has been reported in this work, which shows emission within the range from 800-1650 nm, covering both NIR-II and NIR-III regions, with a quantum efficiency of 35%. Effective Cr3+ → Yb3+, Cr3+ → Er3+, and Yb3+ → Er3+ energy transfers were confirmed. Near-infrared optical thermometry was also developed utilizing the non-thermally coupled 4I13/2→4I15/2 (Er3+) and 2F5/2→2F7/2 (Yb3+) levels, whose highest relative sensitivity (SR), and absolute sensitivity (SA) values were determined as 0.75% K-1 (348 K) and 84.6×10-4 K-1 (373 K), respectively. The KScP2O7: 0.05Cr3+, 0.02Yb3+, 0.01Er3+ phosphor was blended with a commercial low-cost blue LED chip (465 nm) in order to develop NIR-based pc-LED devices, and the highest recorded output power with a value of 38.0 mW (320 mA) was achieved in the studied range. A photoelectric efficiency of 5.9% (10 mA) was also obtained in the NIR region. Through screen printing, the developed phosphor was also proven to be suitable for night vision. This study provides a novel tri-doping approach to design blue light excitable phosphors simultaneously emitting strong NIR-II and NIR-III lights.