Photoluminescence Properties of AScSi 2 O 6 :Cr 3+ (A = Na and Li) Phosphors with High Efficiency and Thermal Stability for Near-Infrared Phosphor-Converted Light-Emitting Diode Light Sources.

Near-infrared (NIR) phosphors are fascinating photoluminescence materials with applications in phosphor-converted light-emitting diodes (pc-LEDs) for night vision lighting, which are still restricted by low efficiency and thermal stability in the current research stage. In this work, AScSi 2 O 6 (A = Na/Li) are chosen as hosts due to a larger band gap and a single octahedral site for Cr 3+ doping. The NIR-emitting Cr 3+ -activated AScSi 2 O 6 :Cr 3+ phosphors were successfully prepared by a common high-temperature solid-state method. X-ray diffraction and Rietveld refinement confirm that the Cr 3+ prefers to enter the Sc 3+ -octahedral lattice site in the AScSi 2 O 6 structure. Under blue light excitation, AScSi 2 O 6 :Cr 3+ phosphors exhibit broadband NIR emission from 700 to 1100 nm with a full width at half-maximum of ∼150 nm owing to the 4 T 2 → 4 A 2 electron transition of Cr 3+ . The photoluminescence properties were enhanced by adjusting the fluxes and sintering conditions, and highly efficient LiScSi 2 O 6 :Cr 3+ NIR phosphors with external quantum efficiencies of 33.4% were obtained. Moreover, the optimized LiScSi 2 O 6 :Cr 3+ exhibits excellent thermal stability (75% at 150 °C) with an activation energy of 0.33 eV. Importantly, the fabricated NIR pc-LED with the highly efficient LiScSi 2 O 6 :Cr 3+ phosphor demonstrates brighter NIR light and a higher luminous efficacy than the NaScSi 2 O 6 :Cr 3+ phosphor in night vision.