Photoluminescence Properties of AScSi2O6:Cr3+ (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, AScSi₂O₆ (A = Na/Li) are chosen as hosts due to a larger band gap and a single octahedral site for Cr³⁺ doping. The NIR-emitting Cr³⁺-activated AScSi₂O₆:Cr³⁺ phosphors were successfully prepared by a common high-temperature solid-state method. X-ray diffraction and Rietveld refinement confirm that the Cr³⁺ prefers to enter the Sc³⁺-octahedral lattice site in the AScSi₂O₆ structure. Under blue light excitation, AScSi₂O₆:Cr³⁺ phosphors exhibit broadband NIR emission from 700 to 1100 nm with a full width at half-maximum of ∼150 nm owing to the ⁴T₂ → ⁴A₂ electron transition of Cr³⁺. The photoluminescence properties were enhanced by adjusting the fluxes and sintering conditions, and highly efficient LiScSi₂O₆:Cr³⁺ NIR phosphors with external quantum efficiencies of 33.4% were obtained. Moreover, the optimized LiScSi₂O₆:Cr³⁺ 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 LiScSi₂O₆:Cr³⁺ phosphor demonstrates brighter NIR light and a higher luminous efficacy than the NaScSi₂O₆:Cr³⁺ phosphor in night vision.