Realization of green emission in AlN:Eu²⁺ phosphors for LED and flexible anti-counterfeiting film applications

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:Eu²⁺ 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:0.05Eu²⁺ 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:Eu²⁺@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:Eu²⁺ phosphors possess significant potential for realizing multidimensional applications in lighting displays and anti-counterfeiting.