Abstract
Europium, terbium, dysprosium, and samarium are the main trivalent lanthanide ions emitting in the visible spectrum. In this work, the potential of these ions for colorimetric applications and colour reproduction was studied. The conversion of spectral data to colour coordinates was undertaken for three sets of Ln complexes composed of different ligands. We showed that Eu is the most sensitive of the visible Ln ions, regarding ligand-induced colour shifts, due to its hypersensitive transition. Further investigation on the spectral bandwidth of the emission detector, on the wavelengths’ accuracy, on the instrumental correction function, and on the use of incorrect intensity units confirm that the instrumental correction function is the most important spectrophotometric parameter to take into account in order to produce accurate colour values. Finally, we established and discussed the entire colour range (gamut) that can be generated by combining a red-emitting Eu complex with a green-emitting Tb complex and a blue fluorescent compound. The importance of choosing a proper white point is demonstrated. The potential of using different sets of complexes with different spectral fingerprints in order to obtain metameric colours suitable for anti-counterfeiting is also highlighted. This work answers many questions that could arise during a colorimetric analysis of luminescent probes.
Highlights
Luminescent trivalent lanthanide (Ln) ions are well known for their unique spiked emission bands due to forbidden f-f transitions [1]
We extended the investigation of the colours of luminescent trivalent lanthanide complexes by looking at the spectral fingerprints of Eu, Tb, Dy, and Sm in three different types of complexes dissolved in aqueous solution
The aim of this part is to compile the colours that can be obtained by using different Ln ions in different ligand environments, thereby exploring the colorimetric shift that can be induced by variations of the ligand field
Summary
Luminescent trivalent lanthanide (Ln) ions are well known for their unique spiked emission bands due to forbidden f-f transitions [1]. Once coupled to organic ligands bearing a light-harvesting chromophore with suitable photophysical properties, most of the Ln ions are capable of producing luminescence by photosensitisation. This process is optimal for Ln(III) emitting in the visible spectrum, such as Eu, Tb, Dy, and Sm. Visible luminescent trivalent Ln ions are easier to sensitise as chromophores absorbing in the UV from 250–380 nm are good energy donors for these Ln acceptors. Eu and Tb are the most efficient emitters of the Ln series, with characteristic emission bands yielding red and green emission colours, respectively. For example, yield white emissions when mixed with the blue emission of some ligands or of the matrix [3]
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