Multi-wavelength optical encoding enabled by excitation-dependent luminescence in rare-earth activated La2O3 phosphors

Multifunctional luminous phosphors with controllable emission properties have been developed in response to the increasing demand for improved photonic and optical security systems. Here, urea was used as fuel in a simple combustion process to create Tm 3+ , Er 3+ , and Tm 3+ /Er 3+ activated La 2 O 3 phosphors. The development of a single-phase hexagonal lattice with improved crystallinity and decreased defect concentration was verified by structural studies. Rare-earth inclusion have affected the lattice strain, crystallite size, and defect density, while co-doping resulted in near-zero net strain and increased structural stability. While co-doped phosphors showed excitation-dependent color tunability through selective excitation and energy-transfer processes, optical investigations showed strong blue emission from Tm 3 ⁺ and high-purity green emission from Er 3 ⁺ (~ 98%). The multi-wavelength luminescence response is promising candidate for next-generation photonic security applications, encrypted barcode authentication, and sophisticated anti-counterfeiting.