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NaMnF3:Yb,Er and NaMnF3:Yb,Er@NaGdF4:xEu (x = 0, 0.3, 0.6, and 0.9) samples were synthesized by a simple hydrothermal method. The as-obtained NaMnF3:Yb,Er particles show a single red emission under the irradiation of infrared light (980 nm), due to the energy exchange transfer process between Mn2+ ions and Er3+ ions. Notably, further growth of NaGdF4:Eu on the basis of NaMnF3:Yb,Er enhanced the green up-conversion luminescence of Er3+ ions, which gradually shifted from red to green with the increase of the Gd3+ ion doping amount. In addition, NaMnF3:Yb,Er@NaGdF4:Eu exhibits red color under ultraviolet excitation (397 nm). These results provide a possible means for controlling the luminescence properties of the lanthanide doped up-conversion system. The luminescent film synthesized with NaMnF3:Yb,Er@NaGdF4:Eu can show different luminescent colors under different light irradiation (near infrared and ultraviolet), which indicates that they have potential applications in multi-mode anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The development of advanced luminescent materials with simple synthesis and a high safety factor is still a great challenge for anti-counterfeiting applications. Herein, multi-mode emission NaYF4:Ln (Ln = Er/Tm, Yb/Er, Yb/Tm)/NaYF4:Ce,Mn composites were synthesized by employing a hydrothermal method. These materials show an excitation source-dependent color change, and could show red, green and blue up-conversion (UC) luminescence under the irradiation of a 980 nm laser and exhibit green and blue down-conversion (DC) luminescence at 254 nm and 365 nm, respectively. The energy transfer mechanism of the UC and DC luminescence of the samples was discussed in detail. Moreover, the composite materials were further fabricated into fluorescent anti-counterfeit inks, and various multi-mode fluorescent patterns were created by screen printing technology. This work provides a simple and promising material with outstanding fluorescence properties for security and anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

The spectroscopic behavior of ionic Eu3+ or Tb3+ complexes of an aromatic carboxyl-functionalized organic salt as well as those of the hybrid materials derived from adsorption of the ionic complexes on Laponite clay are reported. X-ray diffraction (XRD) patterns suggest that the complexes are mainly adsorbed on the outer surfaces of the Laponite disks rather than intercalated within the interlayer spaces. Photophysical data showed that the energy-transfer efficiency from the ligand to Eu3+ ions in the hybrid material is increased remarkably with respect to the corresponding ionic complex. The hybrid material containing the Eu3+ complex shows bright red emission from the prominent 5D0→7F2 transition of Eu3+ ions, and that containing the Tb3+ complex exhibits bright green emission due to the dominant 5D4→7F5 transition of Tb3+ ions. [ABSTRACT FROM AUTHOR]

The acidity of europium(III)-exchanged zeolite L (Eu3+/ZL) and its influence on the luminescence performances of encapsulated europium(III) β-diketonate complexes are reported. The results indicate the importance of understanding the acidity of Eu3+/ZL in the preparation of luminescent host-guest materials of zeolite L crystals and europium(III) β-diketonate complexes. The acidity of Eu3+/ZL was determined roughly by using a dye (thionine) as the probe molecule. The luminescence performances of the host-guest materials, including excitation and emission spectra, lifetime of Eu3+ ions, quantum yield, and energy transfer efficiency, have been investigated. The luminescence behavior of the host-guest materials can be tuned by changing the acidity inside the channels of the zeolite L crystals and can potentially be used as a sensor for detecting ammonia. [ABSTRACT FROM AUTHOR]