Development of flexible luminescent films, photoluminescence properties and anti-counterfeiting applications of SrMoO4:Tb3+ green phosphors

The development of efficient multifunctional phosphors become hotspot in current commercial optoelectronic applications. Here we report, the green light-emitting SrMoO4:Tb3+ (0.01 <= x <= 0.09) phosphors were prepared via solid-state route. The powder X-ray diffraction results revealed that the prepared phosphors were crystallised in a scheelite-type tetragonal phase with space group I4(1)/a and the structural parameters were examined by Rietveld refinement method. The scanning electron microscopy micrographs reveal that the particles exhibit irregular agglomerated morphology. UV-Visible diffused reflectance spectra reveals that, on substitution of Tb3+ ion into Sr2+ site, the direct band gap energy decreases with increasing Tb3+ content from 4.15 to 3.72 eV. In the PL emission spectra of Tb3+-activated SrMoO4 samples excited at 300 nm, the appeared characteristic emission peaks of Tb3+ ions are arose due to the D-5(4) -> F-7(J) (J = 3, 4, 5, 6) transitions. Further, the concentration quenching was observed at SrMoO4:Tb3+ (Tb3+ >= 5 mol%) phosphors due to the exchange interaction between the neighbor Tb3+-Tb3+ ions (Q similar to 3). The chromaticity coordinates of prepared phosphors lie in the green region of the Commission Internationale de I' Eclairage 1931 chromaticity diagram. The calculated lifetime of the Sr0.95Tb0.05MoO4 phosphor excited at 300 nm is 0.57 ms, which is considered to be a long lifetime. Hence, photoluminescence results reflect that the prepared phosphors are potential materials for solid-state lighting applications. Using optimized phosphor (Sr0.95Tb0.05MoO4) and polyvinyl alcohol (PVA) as a matrix, we developed a cost-effective, eco-friendly luminescent security ink in countering counterfeiting of precious documents, branded products, and currencies. In addition, we developed a flexible luminescent film for flat panel devices.