Use of crystal water-free Fe(II) compounds as radiation absorbers

A method of using an absorber of electromagnetic radiation comprising:

• absorbing electromagnetic radiation with the absorber finely distributed or dissolved in a carrier material, wherein the absorber is:
• crystal water-free iron(II) orthophosphate of the general formula Fe3(PO4)2 and being selected from compounds which have a crystal structure comprising transition metal complexes of iron in which the complex does not have an inversion center relative to the central atom, or
• crystal water-free iron(II) metal orthophosphate, iron(II) metal phosphonate, iron(II) metal pyrophosphate or iron(II) metal metaphosphate of the general formula FeaMetb(POc)d, where a is a number from 1 to 5, b is a number from >0 to 5, c is a number from 2.5 to 5, d is a number from 0.5 to 3 and Met represents one or more metals selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, the transition metals (d block), the metals and semimetals of the third, fourth and fifth main groups, and the lanthanoids or combinations of the above mentioned phosphates, and being selected from compounds which have a crystal structure comprising transition metal complexes of iron in which the complex does not have an inversion center relative to the central atom, and
• wherein the carrier material contains the absorber in a quantity such that it absorbs infrared radiation where the wavelength is at least in the region from 780 nm to 1400 nm more strongly than the same carrier material which does not contain the absorber.