Exploring the photo-physical characteristics of transparent, flexible, and green emissive La2CaZnO5:Er3+ nanophosphor encapsulated in PVA/CS films: Applications in anti-counterfeiting, long-term preservation of latent fingerprints, and multi-stimuli responsive shape memory behaviour

Abstract

The aim of this paper was to blend the polymers, Poly(vinyl alcohol) (PVA) and chitosan (CS) to produce a novel composite materials possessing the benefits of both. La2CaZnO5:Er3+ nanophosphors (NPs) were used as a suitable filler to fabricate the blend a nanocomposites (NCs) with desired properties. First, the surface of NPs, was modified with vitamin-B3 (VB3) as a bio-safe coupling agent. Then, the blend NCs with various ratios of modified La2CaZnO5:3% Er3+ VB3 (50, 100, 150 and 200 mg) (L3%ErVB3) were fabricated under ultrasonic irradiations followed by casting/solvent evaporation method. SEM images illustrated the impact of modified NPs on the surface morphology of PVA/CS films, while EDS analysis confirmed the elemental composition of L3%ErVB3 NCs. Photoluminescence (PL) spectra demonstrated a distinct peak at 548 nm, attributing to the 4S3/2→4I15/2 transition. The shape memory behavior of PC@L3%EVB3 (150 mg) NCs were investigated under various conditions including exposure to water, acidic, alkaline environments, and heat. The rate of shape recovery exhibited significant discrepancies depending on the pH levels. Specifically, it took 90 sec for the shape recovery rate to achieve 99% at pH ∼2, while under alkaline conditions (pH ∼13), immersion for 120 sec was necessary to reach a recovery rate of 94%. The transparency, elastic, stretchable, and waterproof NC film, exhibiting excellent concealment, serves as a fluorescence-based platform for in-situ visualization and preservation of latent fingerprints (LFPs). Long-term preservation using PC@L3%EB3 NCs opens avenues in advanced forensic applications. Additionally, an unclonable invisible security ink is developed for safeguarding valuable goods. The NCs application in dynamic anti-counterfeiting (AC) is highlighted, showcasing uniform ink distribution and stability in diverse atmospheric conditions. Notably, PC@L3%EVB3 NCs successfully delayed the ageing process of green grapes, offering a viable way to increase fresh produce shelf life and lessen dependency on single-use petroleum-based packaging in food packaging applications.