Pivotal role of fluxes in BaTiO3:Eu3+ nano probes for visualization of latent fingerprints on multifaceted substrates and anti-counterfeiting applications

Limited energy migration and circumscribed multiphonon relaxation produced non-concentration quenching in a novel dazzling red-emitting phosphor

White LED applications are still constrained by extremely efficient narrow band red emitting phosphors. Meanwhile, the concentration quenching induced by energy migration is the main reason that limits the emission intensity of a red emitting phosphor. Therefore, developing a novel red emitting material with energy migration limitations seems necessary. Here, we proposed and realized the non-concentration quenching doping of Eu3+ ions in a Sr9Y2-2xW4O24:xEu3+ (0 ≤ x ≤ 1.0) phosphor for the first time by means of host preferential selection. By clearly investigating the crystal structure and luminescence kinetics, the long-distance between the nearby Eu3+ ions and the low phonon energy are the main reasons that suppress the energy migration and the cross-relaxation among Eu3+ ions. These advantages result in a high internal (90.47%) and external quantum efficiency (42.1%) of Sr9Eu2W4O24. With the help of the Judd-Ofelt theory and the large value of oscillator strength Ω2, Eu3+ ions are verified to occupy the non-symmetric lattice site with high color purity (94.4%). In addition, only 5.2% emission intensity loss at 140 °C can guarantee its application in LED devices. Moreover, the SYWO:Eu3+ phosphor has high thermal tolerance, high color stability, excellent moisture resistance and superior physical/chemical stability, and thus has broad practical spectral application prospects. The prepared WLED shows superior performance, and the calculated NTSC values are as high as 101.8% and 104.7%, respectively. For comparison, the optical performances of the Sr9Y2W4O24:Eu3+ phosphor outperform those of the standard commercial red phosphors, Y2O3:Eu3+ and Y2O2S:Eu3+, and almost match that of K2MnF6. These results may pave the way for fresh approaches to the study of high-performance Eu3+-activated phosphors.

Enhance photoluminescence properties of Ca-Eu:Y2O3@SiO2 core-shell nanomaterial for the advanced forensic and LEDs applications

The divalent (Ca²⁺)-doped Eu:Y₂O₃@SiO₂ core-shell luminescent nanophosphors have been synthesised by a cost-effective combustion technique. Various characterizations were carried out to confirm the successful formation of the core-shell structure. The TEM micrograph reveals the thickness of the SiO₂ coating over Ca-Eu:Y₂O₃ as ∼25 nm. The optimal value of silica coating over the phosphor has been obtained as 10 vol%(TEOS) of SiO₂, with this value increasing fluorescence intensity by 34 %. Phosphor exhibits CIE coordinates as x = 0.425, y = 0.569 and a CCT value as ∼2115 K with color purity and the respective CRI of 80 % and 98 %, respectively, which make the core-shell nanophosphor suitable for warm LEDs, and other optoelectronic applications. Further, the core-shell nanophosphor has been investigated for the visualisation of latent finger prints and as security ink. The findings point towards the prospective future application of nanophosphor materials for anti-counterfeiting purposes and latent finger prints for forensic purposes.

One material, many possibilities via enrichment of luminescence in La2Zr2O7:Tb3+ nanophosphors for forensic stimuli aided applications

Engineering a single material with multidirectional applications is crucial for improving productivity, low cost, flexibility, least power consumption, etc. To achieve these requirements, novel design structures and high-performance materials are in urgent need. Lanthanide-doped nanophosphors have the greatest strengths and ability in order to tune their applications in various dimensions. However, applications of nanophosphor in latent fingerprints visualization, anti-counterfeiting, and luminescent gels/films are still in their infancy. This study demonstrated a simple strategy to enhance the luminescence of Tb³⁺ (1-11 mol %) doped La₂Zr₂O₇ nanophosphors by conjugating various fluxes via a simple solution combustion route. The photoluminescence emission spectra reveal intense peaks at ~ 491, 546, 587, and 622 nm, which arises from ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions of Tb³⁺ ions, respectively. The highest emission intensity was achieved in the NH₄Cl flux assisted nanophosphor as compared to NaBr and NH₄F assisted samples. The colorimetric images of fingerprints visualized using the optimized nanophosphor on forensic related surfaces exhibit level -III ridge details, including sweat pores, the width of the ridges, bifurcation angle, and the successive distance between sweat pores, etc. These results are decisive parameters that clearly support the statement "no two persons have ever been found to have the same fingerprints". The anti-counterfeiting security ink was formulated using optimized nanophosphor and various patterns were designed by simple screen printing and dip pen technologies. The encoded information was decrypted only under ultraviolet 254 nm light. All the designed patterns are exhibit not just what it looks/feel like and how better it works. As a synergetic contribution of enhanced luminescence of the prepared nanophosphor, the green-emissive films were fabricated, which display excellent flexibility, uniformity, and transparency in the normal and ultraviolet 254 nm light illumination. The aforementioned results revealed that the prepared NH₄Cl flux-assisted La₂Zr₂O₇: Tb³⁺(7 mol %) NPs are considered to be the best candidate for multi-dimensional applications.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.

Interpol review of fingermarks and other body impressions 2016-2019

This review paper covers the forensic-relevant literature in fingerprint and bodily impression sciences from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20 Review%20 Papers%202019. pdf.

Nucleation and self-assembly dynamics of hierarchical YAlO3:Ce3+ architectures: Nano probe for in vitro dermatoglyphics and anti-mimetic applications

Highly efficient blue emitting YAlO₃:Ce³⁺ (1-11 mol%) nanopowders have been fabricated via bio-surfactant Epigallocatechin Gallate assisted ultrasound irradiated sonochemical route. The nucleation and self-assembly dynamics of solids in solutions influences many straightforward normal processes, hence it plays a vital role in materials engineering applications. Nevertheless, the comprehensive nucleation and self-assembly mechanisms of hierarchical architectures still poorly acknowledged. In the present work, we have been exploring the nucleation and stepwise self-assembly dynamics of the YAlO₃:Ce³⁺ (5 mol%) nanopowders into hierarchical architectures. We found that under ultrasound irradiation, nucleation in the solution forms via multi step process and self-assembly was stimulated by intermolecular forces between the nanopowders and external forces. The optimized YAlO₃:Ce³⁺ (5 mol%) nanopowders used as a luminescent labeling agent for visualization of latent fingerprints on various porous and non-porous surfaces under ultraviolet 254 nm light. The obtained results exhibit well defined ridge details with high sensitivity, selectivity and low background hindrance which showed greater advantages as compared to the conventional powders. Extensive fingerprint details, namely the number and distribution of sweat pores in a ridge were clearly revealed. Further, demonstrated the viability of high-performance security labels using optimized sample for practical anti-mimetic applications. The present work, enabling understanding of ultrasound assisted nucleation and self-assembly of nanopowders which impart dermatoglyphics and anti- mimetic applications.