Hui Zhu,Cheng Zhou,Siying Li,Huanhuan Chen,Xuan Shi,Yanyue Li,Pingzhi Zhang,Wei Li,Maxim S. Molokeev,Andrey O. Zolotov,Jing Wang,Zhi Zhou,Mao Xia
Introducing large-radius cations usually causes structural relaxation, leading to a spectral redshift and low optical performance in Cr3+-activated phosphors. Here, MNAl10O17:Cr3+ phosphors are synthesized, and the substitution of large-radius cations induces the abnormal lattice shrinkage of the N site and atomic site splitting of the M site due to the unique hexaaluminate structure, further distinctly improving luminescent properties. To investigate the university of atomic site splitting, a series of phosphors, Na2(1–m)K2mAl10.8O17:0.2Cr3+ and Gd1–nLanMgAl10.8O19:0.2Cr3+, are synthesized, and the variation of their luminescent properties conforms to the expected rule. Finally, Ga3+ ions are introduced to improve the luminescence efficiency. Internal/external quantum efficiencies of the optimal sample are 98.1 and 65.8%, respectively. Meanwhile, an anomalous spectral blueshift indicates the existence of Cr3+–Cr3+ exchange coupling pairs, and a comparative analysis of similar cases is conducted to provide some insights into the luminescence of coupling pairs.
Driven by the demand for miniaturized broadband near-infrared (NIR) light sources, considerable effort has been dedicated to developing Cr3+-activated phosphors. However, in many cases, the multivalent nature of the Cr ion is adverse to achieving highly efficient emission of Cr3+. Herein, strategic Li+ co-doping was employed to boost the NIR emission of BaGe4O9:Cr3+. In the phosphor, Li+ ions play a pivotal role in the distribution of Cr3+ on the two octahedral sites and the elimination of Cr4+ and crystal defects, leading to a 42.9-fold enhancement of Cr3+ emission. The obtained BaGe4O9:Cr3+,Li+ exhibited broadband emission centered at 808 nm, with an FWHM of 177 nm and an internal quantum efficiency of 61.3%. A fabricated pc-LED device utilizing the phosphor showcased an NIR radiant flux of 24.8 mW and a photoelectric efficiency of 8.9% at 100 mA. Furthermore, the application of the pc-LED in bio-imaging, night vision and information encryption was successfully demonstrated.
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