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The design and synthesis of near infra-red absorbing inorganic pigments

The design and synthesis of near infra-red absorbing inorganic pigments
The design and synthesis of near infra-red absorbing inorganic pigments
Materials which exhibit strong absorption in the Near Infra-Red (NIR) region have applications as laser-marking pigments, IR filters in photovoltaics and CCD detectors, medical imaging devices and absorbing coatings in solar thermal collectors. New NIR absorbing materials based on iron (II) and copper (II) frameworks have been designed using knowledge of predicted d-energy levels and associated transitions. Materials from this class have been synthesised and characterised in terms of structure and optical properties.
A family of 13 iron phosphates and fluorophosphates have been obtained using hydrofluorothermal routes and characterised using single crystal X-ray diffraction. These materials show a variety of structural elements with one-, two- and three-dimensional connectivity. For example RbFe3(PO3F)2(PO2(OH)2)F2 has a framework structure consisting of face-sharing FeO4F2 octahedra linked by PO3F tetrahedra, which are orientated such that the fluoride are terminal and line inter-framework space. This includes the first example of a hydrothermally synthesised iron chlorofluorophosphate, (NH4)2Fe(II)Fe(III)(PO3F)2FCl2, which contains sheets of Fe(II)O2Cl4 octahedra linked together by edge-sharing chloride and chains of Fe(III)O4F2 octahedra trans linked by µ2-bridging fluoride.
UV/Vis/NIR spectra have been collected for 49 compounds and correlations between structure and NIR absorbing properties have been derived. A trend in ligand fields across the series SiO4, PO4 SO4 determined SiO4 showing the weakest ligand field making compounds with this ligand most suitable for NIR absorbing applications. Eight of the most promising materials have been tested for their laser-marking properties using a Nd:YAG laser at Merck, Darmstadt. The effect of particles size on the optical and laser-marking properties has been investigated using K2FeP2O7 as an example. The decrease in particle size caused a red-shift in the absorbance maxima, and produced a well dispersed pigment within the test polymer matrix. Out of these eight compounds, Cu2PO4OH and Cu4PO4O exhibited laser-marking properties comparable to other commercial Merck NIR absorbing pigments.
Keates, Adam
110590ff-7603-478d-9700-a13bb58ac37c
Keates, Adam
110590ff-7603-478d-9700-a13bb58ac37c
Raja, Robert
74faf442-38a6-4ac1-84f9-b3c039cb392b

Keates, Adam (2015) The design and synthesis of near infra-red absorbing inorganic pigments. University of Southampton, Chemistry, Doctoral Thesis, 259pp.

Record type: Thesis (Doctoral)

Abstract

Materials which exhibit strong absorption in the Near Infra-Red (NIR) region have applications as laser-marking pigments, IR filters in photovoltaics and CCD detectors, medical imaging devices and absorbing coatings in solar thermal collectors. New NIR absorbing materials based on iron (II) and copper (II) frameworks have been designed using knowledge of predicted d-energy levels and associated transitions. Materials from this class have been synthesised and characterised in terms of structure and optical properties.
A family of 13 iron phosphates and fluorophosphates have been obtained using hydrofluorothermal routes and characterised using single crystal X-ray diffraction. These materials show a variety of structural elements with one-, two- and three-dimensional connectivity. For example RbFe3(PO3F)2(PO2(OH)2)F2 has a framework structure consisting of face-sharing FeO4F2 octahedra linked by PO3F tetrahedra, which are orientated such that the fluoride are terminal and line inter-framework space. This includes the first example of a hydrothermally synthesised iron chlorofluorophosphate, (NH4)2Fe(II)Fe(III)(PO3F)2FCl2, which contains sheets of Fe(II)O2Cl4 octahedra linked together by edge-sharing chloride and chains of Fe(III)O4F2 octahedra trans linked by µ2-bridging fluoride.
UV/Vis/NIR spectra have been collected for 49 compounds and correlations between structure and NIR absorbing properties have been derived. A trend in ligand fields across the series SiO4, PO4 SO4 determined SiO4 showing the weakest ligand field making compounds with this ligand most suitable for NIR absorbing applications. Eight of the most promising materials have been tested for their laser-marking properties using a Nd:YAG laser at Merck, Darmstadt. The effect of particles size on the optical and laser-marking properties has been investigated using K2FeP2O7 as an example. The decrease in particle size caused a red-shift in the absorbance maxima, and produced a well dispersed pigment within the test polymer matrix. Out of these eight compounds, Cu2PO4OH and Cu4PO4O exhibited laser-marking properties comparable to other commercial Merck NIR absorbing pigments.

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Published date: 25 June 2015
Organisations: University of Southampton, Chemistry

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Local EPrints ID: 380915
URI: http://eprints.soton.ac.uk/id/eprint/380915
PURE UUID: 4572660e-039c-415b-a753-d585f6fa76f7
ORCID for Robert Raja: ORCID iD orcid.org/0000-0002-4161-7053

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Date deposited: 22 Sep 2015 12:53
Last modified: 10 Dec 2019 06:38

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Contributors

Author: Adam Keates
Thesis advisor: Robert Raja ORCID iD

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