Two-site occupation in Cr3+-activated BaIn2(P2O7)2 phosphor for broadband near-infrared thermometry and LED applications

Near-infrared (NIR) light sources are essential for biological, machine vision, food analysis, and photonic applications. In this work, a new broadband NIR phosphor BaIn2-x(P2O7)2:xCr3+ (in brief BIP:Cr3+) was synthesized. The crystal structure, microstructure, photoluminescence properties, luminescent lifetime, and thermal quenching of the BIP:Cr3+ phosphor were studied. Under 480 nm irradiation, the BIP:0.02Cr3+ phosphor shows a broadband NIR emission centered at 894 nm, and a full width at half maximum (FWHM) of 163 nm. Adjusting the Cr3+ concentration in the BIP:Cr3+ phosphor can change the position of the emission peak. As the concentration of Cr3+ ions increases, the FWHM rises from 152 to 254 nm and the emission peak wavelength shifts from 892 to 960 nm. The broad spectrum are a result of the overlap of two emission bands centered at 879 and 958 nm, which are caused by the Cr3+ occupying two different six-coordination crystallographic positions of [In1O6] and [In2O6], respectively. The distribution of blood vessels and bones in the palm, as well as the fruit picture taken under the NIR light from the as-fabricated pc-LED, indicates the promise of the BIP:Cr3+ phosphor in broadband NIR pc-LEDs applications. Moreover, the BIP:0.02Cr3+ phosphor exhibits strong temperature-dependent luminescence property indicating that it has great potential in NIR thermometry application.