Sr2(Ga/Al)TaO6:Cr3+ phosphor with tunable near-infrared emitting for light-emitting diodes and optical thermometer

Abstract

Near-infrared (NIR) phosphors is feasible for night vision and optical thermometry applications. We synthesized several NIR/red light-emitting Sr2(Ga/Al)TaO6:Cr3+ phosphors using a high-temperature solid-state reaction approach and then conducted in-depth research on the crystal structure, luminescence properties, quantum yields and temperature dependence of the materials. Adjusting the concentrations of Ga3+ and Al3+ within the tantalate host makes it possible to regulate the crystal field environment containing Cr3+ ions, thereby tuning their emission bandwidth. The occupancy of Cr3+ in Sr2(Ga/Al)TaO6 was discussed based on structural refinement and first principles. The results demonstrated that in the Sr2(Ga/Al)TaO6 host, Cr3+ ions occupied Ga3+/Al3+ and Ta5+ sites, exhibiting narrow-band emission derived from the 2E→4A2 transition and broad-band emission resulting from the 4T2→4A2 transition, respectively. Sr2GaTaO6:Cr3+ phosphor possesses a full width at half maximum of 130.9 nm at 473 K and maintains 67.85% thermal stability compared with ambient temperature when measured at 373 K. The integration of a light-emitting diode (LED) chip and a Sr2GaTaO6:Cr3+ phosphor was prepared as an NIR pc-LED device and applied to night vision, demonstrating its good potential in the field of NIR imaging. Furthermore, in the Sr2AlTaO6 host, the emission of Cr3+ ions at 707 nm (4T2→4A2 transition) and 740 nm (2E→4A2 transition) exhibited opposite temperature dependent characteristics. Using the utilization of fluorescence intensity ratio (FIR) technology, the relative sensitivity of Sr2AlTaO6:Cr3+ phosphor as an optical ratiometric thermometer could reach 2.18% K−1 at 293 K, demonstrating a prospective application for the material in temperature sensing.