Ultrafast preparation of Europium(III) and Terbium(III) activated LaSr₂F₇ nanoparticles for white LEDs and anti-counterfeiting mark

Tunable color-emitting LaSr₂F₇ nanoparticle-based phosphor materials with single- or co-doped trivalent rare-earth ions (Eu³⁺/Tb³⁺) were synthesized via an ultrafast chemical precipitation technique. When Eu³⁺ and Tb³⁺ ions were doped into the LaSr₂F₇ nanoparticles, the photoluminescence behaviors were investigated and showed characteristic red and green emissions in their respective regions. Under 393 nm excitation, the LaSr₂F₇:xEu³⁺ nanoparticles revealed the dominant red emission band (⁵D₀ → ⁷F₁) of Eu³⁺ ions while the optimum doping concentration was obtained at 0.4 mol, indicating a quantum yield (QY) of 24.5%. Likewise, the LaSr₂F₇:yTb³⁺ nanoparticles showed the f-f transition of Tb³⁺ ions and an intense green-emission peak at 543 nm (⁵D₄ → ⁷F₅) was observed under 352 nm of excitation wavelength and the predominant doping concentration was 0.5 mol and the QY was estimated to be about 33.4%. By increasing the Eu³⁺ ion concentration in the optimized LaSr₂F₇:Tb³⁺ phosphors, the color emissions were turned from yellow to red under 365 nm excitation and the existed energy transfer efficiency in between the Tb³⁺ and Eu³⁺ ions was analyzed. Furthermore, the red-, green- and warm white-emitting devices were also fabricated by utilizing the optimal single- and co-doped samples for covering NUV chips. Ultimately, the LaSr₂F₇:Eu³⁺ and LaSr₂F₇:Tb³⁺ nanoparticles were further applied to a high-security ink for stabile anti-counterfeiting mark.