Photoluminescence (PL), up-conversion PL (UCPL), and phosphorescence are three kinds of phenomena common to light-emitting materials, but it is very difficult to observe all of them simultaneously when they are derived from a single material at room temperature. For the first time, triple-mode emission (that is, PL, UCPL, and room temperature phosphorescence (RTP)) is reported, which relies on a composite of the luminescent carbon dots (CDs) prepared from m-phenylenediamine and poly(vinyl alcohol) (PVA). Moreover, the CDs-PVA aqueous dispersion is nearly colorless and demonstrates promise as a triple-mode emission ink in the field of advanced anti-counterfeiting.

Triple-Mode Emission of Carbon Dots: Applications for Advanced Anti-Counterfeiting

Metal–organic frameworks (MOFs) have emerged as particularly exciting inorganic–organic hybrid porous materials which can be simply self-assembled from their corresponding inorganic metal ions/clusters with organic linkers. MOFs can combine the inherent physical and chemical properties of both inorganic and organic photonic units due to their inorganic–organic hybrid nature. Furthermore, the pores within MOFs can also be utilized to encapsulate a large number of guest species as photonic units. The vast combination possibilities, synergistic effects, as well as controllable and ordered arrangements of multiple photonic units (MPUs) have distinguished MOFs from other inorganic and organic photonic materials and enabled them to be a promising platform to realize novel photonic functional applications. In this review, we summarize the recent and important progress in the design and construction of photonic MOFs, as well as their various applications in luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, data storage, and biomedicine. In addition, we highlight the construction strategy and the synergistic effects of MOFs towards achieving high performance and novel photonic functions. Finally, we also outline the challenges in these fields and put forward the prospects and directions for future development.

Photonic functional metal-organic frameworks.

Counterfeiting of valuable documents, currency and branded products is a challenging problem that has serious economic, security and health ramifications for governments, businesses and consumers all over the world. It is estimated that counterfeiting represents a multi-billion dollar underground economy with counterfeit products being produced on a large scale every year. Counterfeiting is an increasingly high-tech crime and calls for high-tech solutions to prevent and deter the acts of counterfeiting. The present review briefly outlines and addresses the key challenges in this area, including the above mentioned concerns for anti-counterfeiting applications. This article describes a unique combination of all possible kinds of security ink formulations based on lanthanide doped luminescent nanomaterials, quantum dots (semiconductor and carbon based), metal organic frameworks as well as plasmonic nanomaterials for their possible use in anti-counterfeiting applications. Moreover, in this review, we have briefly discussed and described the historical background of luminescent nanomaterials, basic concepts and detailed synthesis methods along with their characterization. Furthermore, we have also discussed the methods adopted for the fabrication and design of luminescent security inks, various security printing techniques and their anti-counterfeiting applications.

Future prospects of luminescent nanomaterial based security inks: from synthesis to anti-counterfeiting applications

Traditional smart fluorescent materials, which have been attracting increasing interest for security protection, are usually visible under either ambient or UV light, making them adverse to the potential application of confidential information protection. Herein, we report an approach to realize confidential information protection and storage based on the conversion of lead-based metal-organic frameworks (MOFs) to luminescent perovskite nanocrystals (NCs). Owing to the invisible and controlled printable characteristics of lead-based MOFs, confidential information can be recorded and encrypted by MOF patterns, which cannot be read through common decryption methods. Through our conversion strategy, highly luminescent perovskite NCs can be formed quickly and simply by using a halide salt trigger that reacts with the MOF, thus promoting effective information decryption. Finally, through polar solvents impregnation and halide salt conversion, the luminescence of the perovskite NCs can be quenched and recovered, leading to reversible on/off switching of the luminescence signal for multiple information encryption and decryption processes.

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Conversion of invisible metal-organic frameworks to luminescent perovskite nanocrystals for confidential information encryption and decryption

Food safety is a prevalent concern around the world. As such, detection, removal, and control of risks and hazardous substances present from harvest to consumption will always be necessary. Metal-organic frameworks (MOFs), a class of functional materials, possess unique physical and chemical properties, demonstrating promise in food safety applications. In this review, the synthesis and porosity of MOFs are first introduced by some representative examples that pertain to the field of food safety. Following that, the application of MOFs and MOF-based materials in food safety monitoring, food processing, covering preservation, sanitation, and packaging is overviewed. Future perspectives, as well as potential opportunities and challenges faced by MOFs in this field will also be discussed. This review aims to promote the development and progress of MOF chemistry and application research in the field of food safety, potentially leading to novel solutions.

Metal-Organic Frameworks for Food Safety.

Photoluminescent lanthanide-organic frameworks (Ln-MOFs) were printed onto plastic and paper foils with a conventional inkjet printer. Ln-MOF inks were used to reproduce color images that can only be observed under UV light irradiation. This approach opens a new window for exploring Ln-MOF materials in technological applications, such as optical devices (e.g., lab-on-a-chip), as proof of authenticity for official documents.

Inkjet Printing of Lanthanide–Organic Frameworks for Anti-Counterfeiting Applications

In this work, carbon dots (CDs) prepared by a one-step hydrothermal method were employed for the determination of quercetin in teas and beers. The fluorescence quenching of CDs was proportional to the concentration of quercetin. Under optimum experimental conditions, linear quenching was observed for quercetin in the range of 1.0 to 10 mg L-1 (F/F0 = (0.1511 ± 0.0075)[Q] + (0.8922 ± 0.0384), R2 = 0.9926), at room temperature, using 80 μL CDs and 0.1 mol L-1 Na2HPO4/NaOH buffer solution (pH 11.0). A limit of detection (3σ criterion) of 0.85 mg L-1, and a relative standard deviation of 0.21% (n = 3) for 4.0 mg L-1 quercetin solution was obtained. Addition and recovery tests with tea and beer samples were performed resulting in recoveries at the range between 80 and 118%. This procedure served successfully to determine quercetin in beer and tea samples presenting high sample throughput.

/pdf/use-of-carbon-dots-synthesized-from-citrate-as-a-fluorescent-3m4p9izdgt.pdf

Use of Carbon Dots Synthesized from Citrate as a Fluorescent Probe for Quercetin Determination in Tea and Beer Samples

Preparation, characterization and application of polyelectrolytes/TiO2/CdSe self-assembled films

Improving the Quantum Efficiency of the Lanthanide-Organic Framework [Eu 2 (MELL)(H 2 O) 6 ] by Heating: A Simple Strategy to Produce Efficient Luminescent Devices

Raquel Milani

Papers

Inkjet Printing of Lanthanide–Organic Frameworks for Anti-Counterfeiting Applications

Use of Carbon Dots Synthesized from Citrate as a Fluorescent Probe for Quercetin Determination in Tea and Beer Samples

Preparation, characterization and application of polyelectrolytes/TiO2/CdSe self-assembled films

Improving the Quantum Efficiency of the Lanthanide-Organic Framework [Eu 2 (MELL)(H 2 O) 6 ] by Heating: A Simple Strategy to Produce Efficient Luminescent Devices