The polarized optical spectrum of Er3+in calcium tungstate at 4.2 and 77°K is reported. Radial integrals and spin‐orbit coupling parameter derived from fitting the position of the centers of gravity of theJmanifolds in intermediate coupling areF2=423.89 cm−1, F4=67.995 cm−1, F6=6.667 cm−1, zgr;=2377 cm−1. A first‐order crystal field calculation based on the intermediate coupling states of the free ion is shown to account very satisfactorily for the optical spectrum, paramagnetic resonance, and magnetic hyperfine structure when using⟨ r−3⟩and the nuclear moment measured by atomic beam triple magnetic resonance. The agreement between the experimental and calculated crystalline quantum numbers is encouraging since they were not forced to fit in the calculation. Also, the fact that the⟨ r−3⟩values obtained for a truly free erbium atom can be used for the case of the ion in a crystalline host indicates that the 4fwavefunctions are little affected by the surroundings. The values of the crystal field parameters obtained from fitting the optical spectrum are:C20= 231±7 cm−1, C40= −90±2 cm−1, C60= −0.6±0.5 cm−1,C44=±(852±18) cm−1, C64=±(396±5) cm−1, B6−4=±(75±12) cm−1.The above parameters predict the Stark splittings of the 53 states up to 25 000 cm−1with an rms deviation of 4.4 cm−1. The calculatedgfactors areg∥c(Z1)=1.21, g⊥c(Z1)=8.45, g∥c(Z2)=3.65, g⊥c(Z2)=7.03; the corresponding measured values are 1.247, 8.38, 3.42, and 6.98, respectively. The calculated and measured values of the hyperfine structure constants are:Acalc167= 41.61×10−4 cm−1, Ameas167= (42.5±0.5)×10−4 cm−1, Bcalc167= 290.60×10−4 cm−1, Bmeas167= (293±3)×10−4 cm−1.
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