Study of optical absorption spectra and magnetic susceptibilities of Tm 3+-pyrogermanate (Tm 2Ge 2O 7)

Abstract

The optical absorption spectra of thulium pyrogermanate (Tm 2Ge 2O 7) or TmPG crystal were recorded in the region between 14 000 and 28 000 cm −1 at temperatures 10 and 80 K. Among the observed spectral lines, 21 transitions from the ground 3H 6 to the excited 3F 3,2, 1D 2 and 1G 4 multiplets have been identified using crystal field (CF) analysis. Magnetic susceptibilities and their anisotropies were remeasured between 300 and 23 K and the sign of the latter was correctly determined. The absorption spectra were analysed by diagonalising a total Hamiltonian describing the free ion and CF together in the 91| SLJM J 〉 intermediately coupled basis states spanning the entire 4f 12 configuration of Tm 3+. The magnetic and Mössbauer spectral results were used as additional experimental data for selecting possible ranges of the values of the CF parameters. The spectra did not indicate C 1 symmetry of the crystal field (CF), as proposed from the MS studies of TmPG, but showed higher symmetry as had been earlier suggested by Wardzynska and others from spectral studies of the isomorphous crystals ErPG and DyPG.