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Title: The design and synthesis of near infra-red absorbing inorganic pigments
Author: Keates, Adam
ISNI:       0000 0004 5361 1673
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2015
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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 FeIIO2Cl4 octahedra linked together by edge-sharing chloride and chains of FeIIIO4F2 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.
Supervisor: Raja, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry