Infrared absorption spectra of anhydrous lutetium orthophosphate activated by Nd3+, Eu3+ and Er3+

The IR absorption spectra (40Q-1200 cm-1) of LuPO4, activated by Nd3+, Eu3+, Er3+, are obtained. The introduction of active ions of r.e.e. does not cause noticeable distortions of low resolved spectra. During precise investigation of spectra with a high resolution the redistribution of the line intensities, appearance of bends, change of the shape and non-monotonous shift of absorption line position, especially noticeable when Eu3+ and Er3+ are introduced, are observed. Such behaviour of the spectra is explained by the deformation of coordination polyhedron of r.e.e. cation and the change of the force constants when it is substituted for by r.e.e. ion with a higher number of 4f-electrons. A preferable sensitivity of antisymmetric valent vibration νsub(as) (F) of the anion PO43- to the change of the active ion concentration is pointed out. Non-monotonous character of concentrational behaviour of IR spectra is connected with the complexity of interaction in ternary systems