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31/03/2023

New luminescent materials in plastics

The luminescent materials are compounds capable of emitting visible light or low infrared to the appropriate stimulus.

Thanks to this particularity, these materials are used in many applications such as electronic mechanisms, biological sound, and laser: from iPhones to electric car engines, as well as military jet engines and satellites.

The main applications of these luminescent materials in the plastics sector are found in the coatings or materials for injection (such as PP, PE, PVC, PU, ​​PS, ABS, TPR, EVA, PMMA, nylon, etc.) for applications such as indicators or for high value products against falsification.

Luminescent additives in the market

In the current market there are many additives that exist for obtaining luminescent materials that should be included in plastic of different quantities and with good dispersion.

One example is phosphorus luminescent derivatives, organic products are increasingly used but they can present problems of degradation due to the phenomenon of oxidation or temperature during the production process.

Additives of this type are more well-known because they are rare, or lanthanides, and they are popular for the photoluminescence characteristic. Various lanthanide ions demonstrate luminescence in the spectral regions of close infrared or are visible through irradiation with ultraviolet light.

The wave longitude of these emissions depends on the lanthanide ion used and is known for its chromatic purity, that is to say, its capacity of emitting a very stretched wave longitude, giving a colour characteristic in the case of visible emissions for example. So, the europium emits red light and Terbium a green light, whilst others, such as Holmium and Erbium, they emit infrared waves. The rare earth properties are divided by lightness (LREEs, Light Rare Earth Elements in English) and heaviness (HREEs, Heavy Rate Earth Elements in English).

Europe does not have its own production of these rare earth elements and depends on the importation, mainly from China, that has 37% of the global reserves. For this reason, and for its many applications in specific sectors and high tech, the European Commission has highlighted the rare earth elements such as the materials with the greatest risk of supply and has included them in the list of critical raw materials (RCM, Raw Critical Materials, in English). [1]

Raw materials in technologies

Figure 1. Raw materials used in key technologies for the digital and green transitions and its relative risk of supply.1

New luminescent materials

In response to the presented risk for the supply of rare earth elements, also known as elements in Block f for its position on the periodic table, in recent years academic researchers have studied new complex luminescents due to elements in Block D, very common metal compounds and low cost such as Chromium, Iron, Magnesium and Copper with emissions ranging from near infrared to visible light such as green or red.

Recently AIMPLAS, in collaboration with the University of Venice (Italy), have developed a complex luminescent with high resistance to temperature that allows it to obtain good dispersions in plastic materials and in intense red colouration when exposed to ultraviolet light.

Figure 2: Red luminescence obtained from low ultraviolet light with a luminescent compound developed in AIMPLAS adding a 1% in an epoxy resin.

The metals from Block D used to obtain luminescent compounds are more abundant in the earth’s crust and those that have a risk of supply present a very low level, allowing the obtention of luminescent compounds to more accessible prices in comparison with the rare earth elements.

AIMPLAS has successfully incorporated these compounds with good dispersions both in thermoplastic materials (such as polyethylene or polypropylene) and in resins for coatings (such as epoxy resin).

Luminescent-polyolefins

Figure 3: Luminescent polyolefins obtained through the addition of different compound percentages

[1] RMIS – Raw Materials Information System

Author: Dr. Lodovico Agostinis, Chemical Technology group