Analysis of the crystal structure and optical of stoichiometric SmOF

The relationship between the crystal structure and the crystal field (CF) effect was studied in the hexagonal samarium oxyfluoride (SmOF). The crystal structure of SmOF was refined with the Rietveld method from the X-ray powder diffraction data in the range of 6.5 < 2 theta < 121.4 degrees. The Ar+ ion laser excited luminescence spectra of the Sm3+ ion (4f(5) electron configuration) doped LaOF and GdOF were recorded at 77 and 300 K between 500 and 800 nm. The absorption spectra between 295 and 2055 nm were measured at selected temperatures between 9 and 300 K using the pure hexagonal SmOF. Analysis of the spectra according to the C-3v symmetry for the Sm3+ site in rare earth oxyfluoride (REOF) yielded 195 Stark components out of the total 1001. For the energy level simulation, a model of 20 adjustable parameters was used including the Racah, Trees, and Judd parameters, the spin-orbit coupling constant (zeta(4f)), and B-0(2), B-0(4), B-3(4), B-0(6), B-3(6), and B-6(6) CF parameters. The experimental energy level scheme was well reproduced with a root mean square deviation equal to 17 cm(-1). The CF parameter set was found to be consistent with those for other RE(3+) ions in REOF matrices. Structural data were used to calculate the CF parameters by a modified point charge model. The calculated second-range contribution was too high, whereas the fourth- and sixth-rank contributions were close to the experimental ones. The experimental and calculated CF parameters indicate only slight distortion from the ideal fluorite-type cubic structure.