Ultra-broad Near-Infrared Emitting Phosphor LiInF₄: Cr³⁺ with Extremely Weak Crystal Field

Dueto the extremely weak crystal field strength and strongelectron-photon coupling of the host lattice and the especiallylarge distortion of the [InF6] polyhedron, the LiInF4: Cr3+ phosphors obtain the very broad emissionbandwidth and long emission wavelength. Recent decades have witnessed a major development inbroadbandnear-infrared (NIR)-emitting phosphors because of their potentialapplications in real-time nondestructive examination. These applicationsrequire the emission spectra of phosphors to be as broad as possiblefor efficient performance. Therefore, a blue-light excited LiInF4: Cr3+ phosphor with a NIR emission covering 700-1400nm is successfully synthesized. Under 470 nm excitation, it showsbroadband emission peaked at 980 nm with the full-width at half maximumof 210 nm. The structure and crystal field environment are investigatedin detail, and the LiInF4: Cr3+ possesses aweak crystal field strength and strong electron-phonon coupling.An efficient NIR phosphor-converted light-emitting diode (pc-LED)is fabricated by the prepared LiInF4: Cr3+ phosphorand commercial blue diode chip, generating a NIR radiant flux of 5.54mW at 150 mA drive current. Finally, the NIR pc-LED is successfullyapplied to identify the blood vessel distribution of the hand. Thiswork suggests the potential of LiInF4: Cr3+ phosphorin applications.