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

Abstract

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.