Tunable color emission is achieved in Lu3Al5O12: Tb3+, Eu3+ phosphors for multimode anti-counterfeiting

This study successfully synthesized a new type of color-adjustable Lu₃Al₅O₁₂: Tb³⁺, Eu³⁺ (LuAG) phosphor through the solid-state reaction approach. A comprehensive characterization of this phosphor was conducted, covering aspects such as its crystal structure, luminescence spectra, decay lifetimes, thermal stability, and the mechanism of energy transfer. Tb³⁺ and Eu³⁺ emit distinct green and red luminescence respectively, with the green emission peaking at 543 nm (corresponding to the ⁵D₄→⁷F₅ transition) and the red emission at 591 nm (attributed to the ⁵D₀→⁷F₁ transition). As the doping concentration of Eu³⁺ rises, the emission color shifts from green to yellow, which is due to the energy transfer from Tb³⁺ to Eu³⁺. Using Dexter’s theory of energy transfer in conjunction with Reisfeld’s approximation, it was determined that the dominant mechanism for energy migration involves electric quadrupole-quadrupole interactions. When the temperature of the phosphor varies from 303 K to 533 K, it shows an excellent abnormal thermal quenching property. In addition, based on the thermal sensitivity of fluorescence intensity ratio, the non-thermal coupled levels of Tb³⁺ and Eu³⁺ are used for optical temperature measurements. Therefore, this phosphor can be used as a multi-mode dynamic anti-counterfeiting material, providing complex anti-counterfeiting performance and making the anti-counterfeiting strategy more secure.