Ligand Field Spectra of Some New Laser Chelates

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Abstract
The high‐resolution emission spectra from microcrystals of three new europium benzoylacetonate chelates, EuB4HP, EuB4HM, and EuB4HD, are presented and discussed in terms of the ligand field symmetries. It is established that the ligand fields about the Eu3+ in these compounds must be of one of the point symmetries C1, C1h, C2, or C2v; however, the exact symmetry in each case cannot be determined from the evidence presented. The emission spectra of EuB4HP and EuB4HM are found to be identical, indicating that the ligand field magnitudes and symmetries are the same for these cases. The emission spectra of EuB4HD, on the other hand, is considerably different, indicating that the magnitude and/or the symmetry of the ligand field in this compound must be different from the other chelates. A vibronic energy level for EuB4HP, probably corresponding to an europium molecular vibrational mode, was determined to be 37 cm—1 above the 5D0 energy level, and 33 cm—1 above the 7F0 energy level. A general tendency is noted in these spectra for the lines terminating on the higher ligand energy levels to be shaded toward longer wavelengths. This may be attributed to the greater number of vibronic states which are closer and more thoroughly mixed with the higher‐lying ligand field states.

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