Understanding the broadband near-infrared luminescence in a highly distorted garnet Ca4HfGe3O12:Cr3+ phosphor.

Broadband near-infrared (NIR) spectroscopy generated from a phosphor-converted light-emitting diode (pc-LED) has multifunctional applications, including food-quality analysis, bio-medical and night-vision, stimulating the demand for developing various NIR phosphors with desired properties. Herein, we selected a highly distorted garnet Ca4HfGe3O12 as the host and explored the near-infrared luminescence of Cr3+. As expected, this material achieved a long-wavelength NIR emission and excellent absorption efficiency based on the effect of Jahn-Teller distortion. The synthesized Ca4HfGe3O12:Cr3+ phosphor exhibits a broadband NIR emission peaking at 840 nm with a full width at half maximum of 150 nm, and the absorption efficiency reaches 48.0%. However, the internal quantum efficiency of the 6 mol% Cr3+-doped sample was measured to be only 35.3% and the integral emission intensity at 373 K kept only 60.1% of the initial intensity. The possible reasons for the unsatisfactory internal quantum efficiency and thermal stability were systematically analyzed, which provided a comprehensive understanding of the relationship between the crystal structure and the luminescent properties of Cr3+-activated garnet-type phosphors. Nevertheless, the as-prepared NIR pc-LED device exhibits a NIR output of 16.52 mW with a NIR photoelectric conversion efficiency of 5.92% driven by 100 mA current, indicating the potential of this material for application in NIR pc-LED.

An efficient and thermally stable near-infrared phosphor derived from the Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) garnet family.

A broadband near-infrared (NIR) light source based on a phosphor-converted light-emitting diode (pc-LED) has attracted increasing interest to be used in non-destructive examination, security-monitoring and medical diagnosis fields, which stimulates the exploration of NIR phosphors with high performance. Herein, a series of Cr3+-activated garnet Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) phosphors were reported, allowing an emission peak ranging from 726 to 822 nm. Among them, Y3ScInGa3O12:Cr3+ with an optimized Cr3+-doping concentration of 6 mol% exhibits a high internal quantum efficiency (IQE = 83.1%) and excellent absorption efficiency (AE = 44.2%) under 450 nm blue light excitation, enabling an external quantum efficiency as high as 36.7%. Moreover, this material can maintain 93.0% of the initial intensity when heated up to 423 K, implying outstanding thermal stability. Finally, a prototype NIR pc-LED device was fabricated by coating the optimized phosphor on a 455 nm LED chip, which generates a broadband NIR emission with a peak located at 765 nm and a full width at half maximum of 127 nm. The NIR output power and NIR photoelectric conversion efficiency of this device were found to be 38.01 mW and 11.0%, respectively, under 100 mA driving current, demonstrating the feasibility of this material to be applied in NIR pc-LEDs.