Nephelauxetic effect and 〈r(k)〉₄f radial integrals of Tm³⁺ in crystals.

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 Tm(3+) ions. The radial expectation values for 4f electrons 〈r(k)〉4f of Tm(3+) 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 〈r(k)〉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.