n juin 2020, l'EUIPO a publié un rapport révélant que la contrefaçon entraîne des pertes économiques majeures en Europe, avec des importations illégales estimées à 121 milliards d'euros par an. Ce phénomène touche divers secteurs, y compris les produits du quotidien, et représente un risque pour la santé et la sécurité des consommateurs. Il favorise également le crime organisé, nécessitant ainsi le développement de solutions de marquage innovantes, écologiques et difficiles à reproduire. Les marqueurs luminescents, notamment les luminophores, sont couramment utilisés pour lutter contre la contrefaçon. Ces matériaux, constitués d'une matrice hôte et d'ions dopants, émettent de la lumière sous excitation. Jusqu'à présent, les recherches se sont principalement concentrées sur les ions de terres rares, malgré les défis environnementaux et géopolitiques liés à leur extraction. Cette thèse explore donc une alternative basée sur les métaux de transition comme le manganèse, le nickel et le chrome, qui offrent des propriétés optiques adaptées aux marqueurs anti-contrefaçon. L'objectif est de concevoir de nouveaux luminophores dopés par des ions de transition, émettant dans le proche infrarouge sous excitation visible ou IR. Ces matériaux seront intégrés dans des matrices polymères et imprimés sous forme de motifs luminescents par des techniques 2D et 3D. En parallèle, l'étude approfondira la spectroscopie de ces ions, encore peu documentée. Les synthèses suivront différentes approches (solvothermale, sol-gel, thermolyse, état solide) pour contrôler la taille et la structure des luminophores. Les propriétés des matériaux seront caractérisées via diffraction des rayons X, spectroscopies IR et Raman, microscopie électronique et diffusion dynamique de la lumière. L'étude des propriétés optiques inclura des mesures spectrales et temporelles de photoluminescence, ainsi qu'une évaluation de la stabilité sous contraintes thermiques et photoniques. Les luminophores les plus performants seront ensuite intégrés à des composites luminescents pour une application concrète au marquage anti-contrefaçon.
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In June 2020, the European Union Intellectual Property Office (EUIPO) published a report assessing counterfeiting-related losses for industries in Europe. The economic and social impact highlighted by the report runs into billions1. According to estimates by this European office, counterfeit products imported into the European Union are worth 121 billion euros a year. Counterfeiting spares no sector, affecting luxury goods as well as everyday products such as toothbrushes, toys, garden equipment, etc., and even everyday consumer goods. Beyond the obvious economic impact2, the Executive Director of the European Office points out that counterfeit products “are likely to promote serious forms of organized crime” and “present obvious risks to consumer health and safety”. In this context, it is crucial to develop innovative marking solutions that are simple to produce, inexpensive, environmentally friendly and difficult to reproduce. This is the background to this thesis.

Many marking solutions use luminescent materials, also known as “phosphors”. These materials can emit light when excited by a light source, and consist of a host matrix, usually an inorganic material, and one or more dopant ions conferring the light-emitting properties. Most studies on phosphors for anti-counterfeiting marking focus on UV-visible conversions, in the form of Down-Shifting (DS) or Down-Conversion (DC) mechanisms. There are also IR-visible and even IR-UV conversion mechanisms, known as Up-Conversion (UC). All in all, tunable emissions are possible thanks to the multiple energy levels of the activators.

Rare earth ions are often used as dopants in these markers because of their remarkable optical properties. However, it is important to point out that their extraction poses significant environmental, geopolitical and social problems. For these reasons, this thesis will focus on the use of transition metals such as manganese, nickel, etc., as doping ions.

The subject of this thesis will focus specifically on the development of new luminescent markers doped with transition ions and emitting in the near infrared under visible/IR excitation, with the aim of creating a new generation of anti-counterfeiting markers. The optical property will be provided mainly by transition ions such as Mn5+, Cr3+ or Ni2+, inserted as dopants in inorganic matrices3,4. These ions are characterized by relatively narrow or broad emissions in the near-infrared range, the color of which can be modulated by an appropriate choice of host structure. These IR fluorescent tracers can be encapsulated in a polymer matrix to design a composite material in the form of a luminescent pattern via 2D printing techniques (inkjet, screen printing, etc.) as well as 3D printing. From a fundamental point of view, this project will also enable us to delve deeper into the spectroscopy of these ions, which is currently under-documented.

The synthesis strategies will include processes in solution to produce inorganic compounds of controlled size (solvothermal synthesis, sol-gel process, thermolysis), as well as more conventional techniques such as solid-state synthesis. The structural and morphological properties of the phosphors produced will be analyzed using techniques such as X-ray diffraction, IR and Raman spectroscopies, scanning and transmission electron microscopies, and dynamic light scattering for smaller particles. Optical properties and energy transfer mechanisms will be studied using spectrally and temporally resolved photoluminescence spectroscopy, recording emission and excitation spectra, as well as fluorescence decays. The evolution of the optical properties of luminescent materials will be investigated under thermal and/or photonic stress to assess their stability. The highest-performance phosphors will be used to produce luminescent composite materials using different printing techniques, with a view to their application in anti-counterfeiting marking.
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Début de la thèse : 01/10/2025

Funding category: Contrat doctoral

Concours pour un contrat doctoral