Guang-Xin Xiang,Guo-Jun Wang,Zhi-Jun Zhang,He Feng,Jing-Tai Zhao,Jiao Wang,Xin-Yuan Sun,Ri-Hua Mao,Yong Wang
The uniform 1D nano-rods of RE 3+ doped Ln 7 O 6 F 9 ( Ln = Y and Lu; RE = Pr, Sm and Eu) were synthesized through a facile two-step hydrothermal method without extra fluorine source followed by post-heat treatment. The phase formation, morphologies, as well as photoluminescence properties of the materials were investigated. The precursor composition was determined to be Ln (OH) 1.69 F 1.31 using the Fourier transform infrared spectrum (FT-IR), thermal gravimetric and differential scanning calorimetry (TG-DSC). The average lengths of Y 7 O 6 F 9 and Lu 7 O 6 F 9 were about 6.8 and 7.9 μm, respectively, with the average width of about 650 nm. It was interesting that the tip of the nano-rods exhibits a straight line and divergent umbrella shaped bifurcation for Y 7 O 6 F 9 and Lu 7 O 6 F 9 , respectively. Upon ultraviolet excitation, Pr 3+ , Sm 3+ and Eu 3+ ions in Ln 7 O 6 F 9 showed blue, orange and red emissions originating from their characteristic f-f transitions. In addition, the 4 f 1 5 d 1 → 4 f 2 band emissions (340–450 nm) as well as typical 4 f 2 → 4 f 2 line emissions (450–700 nm) of Pr 3+ were observed in Pr 3+ -doped Ln 7 O 6 F 9 . For Sm 3+ -doped Ln 7 O 6 F 9 , only the typical f - f transitions of Sm 3+ were observed with the absence of charge transfer (CT) band. However, the broad excitation bands at 255 nm attributing to the charge transfer transition of Eu 3+ (i.e. O 2− → Eu 3+ CT) were observed in Eu 3+ -doped Ln 7 O 6 F 9 .
Metal halide perovskites (MHPs) have sparked ongoing research interest due to their high-performance optoelectronic properties. However, blue-light excitable near-infrared (NIR) emitting MHPs is still inaccessible and the achievement of robust thermal-quenching resistance so far remains a huge challenge. In this work, we report on the synthesis of lead-free all-inorganic Mn 2+ -based perovskite-like single crystals using the designed nonstoichiometric precursor ratio. The special crystal structure endows Mn 2+ with efficient blue light excitation and red emission, which enables the capabilities of a good matching with commercial blue LED chips and an efficient sensitization for Ln 3+ emitters. The incorporations of Yb 3+ , Er 3+ , and Ho 3+ functionalize the CsMnCl 3 single crystals with multiple NIR emissions by virtue of feeding the energy from Mn 2+ to Ln 3+ via multi-channels. Most remarkable is the achievement of the robust thermal-quenching resistance, exhibiting (near-) zero-thermal-quenching and even anti-thermal quenching, of the Ln 3+ NIR emissions above room temperature . Finally, as a proof-of-concept study, a prototype of an NIR-LED device was fabricated. This work not only provides a general strategy to unlock the blue-light excitable NIR emission from f-f transitions of Ln 3+ ions, and a fundamental understanding of the sensitization-activation mechanisms in Ln 3+ -functionalized manganese (Ⅱ)-based perovskite-like phosphor, but also endows the MHPs with optical functionalities for the future high-potential applications, such as NIR phosphor-converted LEDs, and optical telecommunication.
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