Broadband near-infrared phosphor LiTi2(PO4)3:xCr3+ realized via multi-site occupation

Abstract

Near-infrared phosphor-converted light-emitting diodes (NIR pc-led) have wide applications in fields of biological imaging and food detection. However, developing an efficient, inexpensive, and broadband near-infrared fluorescent phosphor with sufficient spectral coverage remains a huge challenge. Herein, we report the synthesis of a series of broadband near-infrared phosphors, LiTi₂(PO₄)₃:xCr³⁺ (LTP), and analyze their crystal structure, luminescent properties, and thermal quenching mechanism. The experimental results indicated that at x = 0.07, the luminescence intensity of the LTP:0.07Cr³⁺ sample reached its maximum value, followed by the concentration quenching phenomenon, which resulted from the energy transfer between the adjacent Cr³⁺–Cr³⁺. Under 455 nm excitation, LTP:0.07Cr³⁺ exhibited a broadband emission spectrum in the range of 700–1250 nm, with a peak centered at 890 nm and a full width at half maximum (FWHM) of 210 nm. The analyses of the crystal structure and PL spectra as well as the calculation of Cr³⁺ crystal field intensity indicated that the realization of a broadband near-infrared emission was attributed to the occupancy of Cr³⁺ at multiple sites of Li⁺ and Ti⁴⁺ in a weak crystal field (Dq/B = 1.92). At a high temperature of 373 K, the luminescence intensity of LTP:0.07Cr³⁺ was 41% of that observed at room temperature, indicating that the thermal stability of the fluorescent phosphor needed further improvement. Finally, NIR pc-LED devices were prepared using the fluorescent phosphor and blue LED chips, confirming the potential application value of the fluorescent phosphor in biomedical imaging, night vision, and food detection.