Phosphors play an extremely important role in solid-state lighting and full-color displays. Recently, it has been observed that their properties can be extensively utilized in the field of anti-counterfeiting. For the study of innovative anti-counterfeiting materials, the selection of high-quality matrix materials is indispensable. In this work, green AlN:Eu 2+ phosphors are synthesized by the direct nitriding method, and their physical structure, micro-morphology, elemental composition, and photoluminescence properties are systematically investigated at different synthesis temperatures and doping concentrations. The results show that the peak emission of AlN:0.05Eu 2+ occurs at 525 nm at a synthesis temperature of 1400 °C, and the fluorescence intensity retains 53.5% of its room temperature value when the test temperature is increased to 110 °C. The synthesized phosphors are dispersed in thermoplastic polyurethane (TPU) to create a UV-excited, flexible anti-counterfeiting film. The AlN:Eu 2+ @TPU anti-counterfeiting film exhibits excellent light transmission, flexibility, stretchability, and water resistance. When a current of 50 mA is applied, the green LED encapsulated with AlN exhibits high color purity. The CIE coordinates of the white LED are (0.32, 0.34), with a relevant color temperature (CCT) of 5727 K and a color rendering index (Ra) of 85.9. Overall, the results suggest that AlN:Eu 2+ phosphors possess significant potential for realizing multidimensional applications in lighting displays and anti-counterfeiting.
AlN based phosphors have a wide range of applications and the green and blue emission of AlN:Eu 2+ phosphors have been reported a lot, while we found yellow emission in this phosphor. In this work, a series of different concentrations of Ca 2+ -doped AlN:Eu 2+ phosphors have been successfully prepared by a freeze drying assisted combustion synthesis, of which the crystal structure, morphology, photoluminescence properties and luminescence mechanism were studied in detail. The results show that Ca 2+ ions have been successfully doped into the AlN:Eu 2+ lattice and cause the lattice distortion, which has a great influence on the luminescent properties of the phosphors. Under the 365 nm excitation, the phosphors present a single emission peak, which is ascribed to the 4f 6 5d-4f 7 transitions of Eu 2+ ions. Furthermore, by increasing the doping amount of Ca 2+ ions (0.1, 0.5, 1 and 3 at %), the emission wavelength can be tuned from 516 to 535 nm, corresponding to the emission color from green to yellow, which is owing to the enhancement of the crystal field intensity around Eu 2+ ions through the interaction between Ca 2+ and Eu 2+ ions. Tuning of the emission wavelength for AlN:Eu 2+ phosphors is of great importance in expanding the applications of AlN:Eu 2+ phosphors in various luminescent fields.
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