Comparison of the spectroscopic and crystallographic data of Tm3+ in the different hosts:: KLn(MO4)2 where Ln=Y,La,Lu and M=Mo,W

Raman scattering and polarised infrared spectra of the potassium rare-earth double molybdates and tungstate (KLn(x)Tm(1-x)(MO4)(2), where Ln=La,Y,Lu, M=Mo,W) were measured at ambient temperature in the range of 40-1000 cm(-1). The assignment of the observed bands to the respective internal and external vibrational modes is proposed. The X-ray structural analysis of the yttrium thulium molybdate and lanthanum thulium tungstate crystals is reported. The crystal structure of the compounds studied depends on the type of cation and changes from monoclinic (for the lanthanum-thulium molybdate) to orthorhombic (for the yttrium- and lutetium-thulium molybdates). The character of the coordination sphere around the molybdenum atom changes from octahedral to tetrahedral. (C) 2002 Elsevier Science B V All rights reserved.