{'fraction_non_alphanumeric': 0.02454642475987193, 'fraction_numerical': 0.022411953041622197, 'mean_word_length': 5.130718954248366, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
4fN − 1 5d energy levels of lanthanides: a quasi-angular-momentum approach and its application to Cs2NaYF6:Er3+

The spin–orbit interaction of the 5d electron needs to be taken into account to give the proper energy structure for the 4fN − 15d configuration of heavy lanthanide ions occupying a site with ligands forming an octahedron. This paper derives theoretical results for the energy structure by treating the t2 orbitals as quasi p orbitals and then using angular-momentum coupling techniques. An analytic expression for the electric dipole absorption line strengths between 4fN multiplets and 4fN − 15d states is given in terms of various angular-momentum quantum numbers and re-coupling coefficients. The result is then applied to interpret the excitation spectrum of Cs2NaYF6:Er3+. The high-spin and low-spin states of Cs2NaYF6:Er3+ are discussed in terms of the wavefunctions obtained by using the developed theoretical model.