Study and applicability of photoluminescence properties of Cr4+: LiInGeO4

This paper reports a series of Cr4+: LiInGeO4, based on a high-temperature solid-phase synthesis method and the effect of LiInGeO4-doped Cr4+ ions on the spectral properties and luminescence colors in the near-infrared region. Under 808 nm excitation, the emission spectra showed a broad band at 1000–1500 nm, with a maximum peak occurring at 1218 nm due to the 3T2→3A2 transition of Cr4+ ions. The lifetime decreases with the increasing amount of Cr4+ ions, from 8.30035 μs to 6.656 μs. The chromium's chemical composition and valence state in LiInGeO4 were analyzed by x-ray photoelectron spectroscopy. The results showed that the chromium in LiInGeO4 was tetravalent, and no trivalent chromium was found. The results show that LiInGeO4 crystals can have promising applicability in anti-counterfeiting due to the possibility of both up-conversion and down-conversion glowing.