Dependence of the optical spectrum of MnF4−6 on the Mn2+–F− distance

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Abstract
We have measured by means of photoluminescence the energy of crystal‐field peaks for RbCdF3: Mn2+ and KZnF3: Mn2+ where the value of the Mn2+–F− distance, R, derived by EXAFS is R=2.13±0.01 Å and R=2.08±0.01 Å, respectively. From these data and those for RbMnF3 and KMnF3 we have studied the dependence on R of the B, C, and 10 Dq parameters for the MnF4−6 complex. This analysis reveals that within the experimental errors, B and C are constant in the range 2.07<R4−6, which also predict that 10 Dq=KR−n, where K and n are constant. The present study confirms this dependence, n being 4.4 which is also in accord to the theoretical predictions. The best values of R derived from optical spectra are found to be R=2.141±0.004 Å (for RbCdF3: Mn2+) and R=2.075±0.004 Å (for KZnF3: Mn2+). The present analysis also points out that by measuring the changes induced on the optical spectrum of MnF4−6 in a given lattice we can detect changes in the Mn2+–F− distance down to 10−3 Å. In this way we have derived the difference, ΔR, between R at room temperature and at 77 K for KZnF3: Mn2+. The obtained value ΔR=(9±1)10−3 Å is in agreement with the one ΔR=(10±3.5)10−3 Å derived previously from the variations undergone by the isotropic superhyperfine constant As. Finally the present results are compared to those for some complexes of Eu2+, Co2+, Ni2+, and Cr3+.