The near-infrared (NIR) spectrum contains characteristic vibrational absorption bands of numerous organic functional groups. NIR phosphor-converted light-emitting diodes (pc-LEDs) have gathered increasing interests in fields including non-destructive testing and night vision. In 2016, Osram reported the first NIR pc-LED, SFH4735, while with low output power (16 mW @ 350 mA) and limited wavelengths. Furthermore, luminescent contrast agents operating within the second biological imaging window (1000-1800 nm) exhibit lower tissue absorption and scattering coefficients in contrast to the traditional first window (750-950 nm), thereby enabling enhanced detection depth and improved imaging signal-to-noise ratio. Significantly, the luminescence of Cr 3+ via engineering the crystal field environment is located in the NIR-Ⅰ region, as illustrated by the Tanabe-Sugano diagram. The presence of Cr 4+ ([Ar]3d 2 ) is capable of extending the emission to the NIR-Ⅱ region, but the efficiency is subpar due to poor luminescence thermal quenching at room temperature. In contrast, phosphors doped with lanthanide ions typically exhibit narrow-band multiplets emission, making spectral tuning a challenging task. Hence, it becomes crucial to investigate methods for achieving broadband NIR-Ⅱ luminescence through ion doping and structural composition.
In a new paper published in Light Science & Application , a team of researchers, led by Professor Quanlin Liu from School of Materials Sciences and Engineering, University of Science and Technology Beijing, China, and co-workers have developed the first-ever NIR-Ⅱ broadband luminescence based on intervalence charge transfer (IVCT) of Cr 3+ -Cr 3+ → Cr 2+ ,Cr 4+ in magentoplumbite-type LaMgGa 11 O 19 . Based on heavily incorporation of Cr 3+ ion, LaMgGa 11 O 19 exhibits dual-emission (NIR-Ⅰ, 890 nm and NIR-Ⅱ, 1200 nm) with a full width at half maximum (FWHM) of 626 nm and luminescence external efficiency of 18.9%. They further observed the luminescence anti-thermal quenching behavior (432% @ 290 K vs @80 K) of target NIR-Ⅱ luminscence.
They observed the NIR-Ⅰ luminescence at low concentration of Cr 3+ ions, whereas the NIR-Ⅱ luminescence appears as the concentration of Cr 3+ ions increases to 0.5. With a high doping concentration of Cr 3+ ions, the excitation and absorption signals of Cr 4+ ions cannot be traced. Additionally, in contrast to the Cr 4+ ions, they discovered significantly longer luminescence decay lifetime (2.3 ms) associated with this anomalous NIR-Ⅱ luminescence. The potential application of LaMgGa 11 O 19 :Cr 3+ phosphor as a light-emitting converter in non-destructive analysis, tissue penetration, and long-distance night vision is demonstrated via fabricating a NIR pc-LED.
Light Science & Applications
25-Jul-2023