Nephelauxetic effect and 〈rk〉4f〈rk〉4f radial integrals of Tm3+ in crystals

•The nephelauxetic ratios βk = Fk (Tm3+)/Fk (Tm IV), k = 2, 4, 6, have been determined.•24 compounds of Tm3+ in stoichiometric or activated crystals have been included.•The model of dielectric screening yields crystal-dependent radial integrals 〈rk〉4f〈rk〉4f.•The applied model relates spectroscopic, structural and dielectric properties.

Bonding and covalency parameters have been evaluated from the nephelauxetic ratios βk = Fk (crystal)/Fk (free ion), with k = 2, 4, 6, for 24 halide and chalcogenide crystals containing Tm3+ ions. The radial expectation values for 4f   electrons 〈rk〉4f〈rk〉4f of Tm3+ ion in certain complex oxides, fluorides, and a sulfide have been determined by means of experimental Slater parameter shifts ΔFk relative to the Fk   values for the free ion Tm IV. The 〈rk〉1f〈rk〉1f values derived in the dielectric screening model have been compared with those computed by different types of 4f wave functions as well as with other estimates.

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