Investigations on the electronic structure of double phosphates of the type M3RE(PO4)(2) (RE equals rare earths, lanthanides)

Optical measurements were reported about the Vacuum-UV absorption edge of alkaline rare-earth orthophosphates. These results are discussed with respect to the spectrocopic properties of eulytite-like compounds and in relation to a diphosphate lattice. The investigation of these insulator materials has shown that band gap is in first line determined by the type of anion structure. Therefore, the above-mentioned double phosphates show a similar behavior of the absorption edge as monazite- and eulytite-type orthophosphate crystals, respectively. Near ultraviolet region optical properties are determined by situation in 4f levels.