A novel Lu₂SrAl₄SiO₁₂:Sm³⁺ orange-red phosphor with ultra-high color purity for WLEDs and anti-counterfeiting inks

A novel class of orange-red emitting Lu₂SrAl₄SiO₁₂:xSm³⁺ phosphors was synthesized via a high-temperature solid-state reaction. Rietveld refinement confirmed that Sm3+ dopants successfully substitute Lu³⁺ sites within the cubic garnet matrix. Under 405 nm near-ultraviolet excitation, the phosphors exhibit intense orange-red emissions, with the dominant peak at 618 nm originating from the ⁴G_5/2 → ⁶H_7/2 transition. Investigations reveal that the maximum luminescence output is achieved at a doping level of x = 0.03. Beyond this point, the concentration quenching process is dominated by dipole-dipole interactions, with the critical energy transfer distance calculated to be 18.88 Å. The optimized phosphor (x = 0.03) exhibits an internal quantum efficiency of 16.7% and a fluorescence lifetime of 2.16 ms. It demonstrates robust thermal stability, retaining 68% of its initial intensity at 423 K. The activation energy governing this thermal quenching process is determined to be 0.187 eV. All single-doped samples exhibit ultra-high color purity exceeding 98.4%. By blending the Lu₂SrAl₄SiO₁₂:0.03Sm³⁺ phosphor with commercial blue/green phosphors on a 405 nm n-UV chip, a high-performance white light-emitting diodes device were fabricated, achieving a warm correlated color temperature of 4318 K and a high color rendering index of 84.53. Furthermore, its successful application as security inks across diverse substrates confirms Lu₂SrAl₄SiO₁₂:0.03Sm³⁺ as a highly promising dual-functional material for advanced solid-state lighting and optical anti-counterfeiting.