The absorption spectrum of single crystal NdF3 of tysonite structure was recorded at liquid helium temperature up to 33 800 cm−1. 127 Stark levels were obtained and fitted to a mean square deviation of 24 cm−1 with a Hamiltonian involving 12 free atom parameters and four D3h crystal field parameters. The fit was improved to a mean square deviation of 14 cm−1 by adding five supplementary crystal field parameters to approach the real C2 symmetry of the site. The paramagnetic susceptibilities parallel and perpendicular to the trigonal axis in the structure were measured from 4.2 to 1100 K and compared with the values derived from the wave vectors of the 18 lowest Kramers doublets through the application of the Van Vleck formula. An overall good agreement was found. The material is anisotropic, χ∥ being larger than χ⊥.

Fluorescence spectra have been analyzed at 4.2, 77, and 300 K and crystal field calculations have been performed on Na5Eu(MO4)4 (M=Mo, W) powders. The two sets of crystal field parameters are almost identical yielding a rms deviation of 5 cm−1. The values are (in cm−1): B20 =200 (180), B40 =−326 (−330), B44 =−863 (−852), B64 =−442 (−416), and B66 =−327 (−339) for Na4Eu(MoO4)4 and Na5Eu(WO4)4, respectively. Wave functions derived from the simulation were applied to the calculation of the temperature dependent paramagnetic susceptibility. Comparisons with experimental average paramagnetic susceptibilities, measured between 4.2 and 300 K, are very satisfactory.

The absorption spectrum of pure rhombohedral NdAlO3 was determined at 4.2 K from 10 000 to 34 000 cm−1. Adding the levels determined for the 4I multiplet by other authors, a total of 117 Stark levels was obtained. They were fitted to a mean square deviation of 13 cm−1 with a Hamiltonian involving 12 free atom parameters and six D3 crystal field parameters applied on the 364 kets basis in the 4f3 configuration. The values are B02=−481 cm−1, B04 =481 cm−1, B34=−390 cm−1, B06=−1700 cm−1, B36=−950 cm−1, B66=−1080 cm−1. Free atom parameters are very close to those of Nd3+ in LaCl3. The powder paramagnetic susceptibility was measured from 4 to 1000 K. The 1/χ versus T curve shows a pronounced curvature, even below 300 K, which is fairly well reproduced by a crystal-field-only calculation involving the complete wave vectors of the 18 lowest Kramers doublets.

The high-temperature polymorph &Y2WO6 is orthorhombic, space group P212121, with a = 8.591 (5), b = 20.840 (10), c = 5.233 (5) .A,Z= 8, Din= 6.38, Dc 6.49 Mg m -a. The structure was determined at room temperature from 454 diffractometer intensities and refined to R = 0.067. The W atoms are octahedrally coordinated and far apart from each other. The four non-equivalent Y atoms have an eightfold (3) and sevenfold (1) coordination number. Reference is made to the fluorescence spectrum of the Eu-doped compound and a comparison is made with the homologous compounds Ln2WO6 (Ln = La to Lu).

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