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A spectroscopic study of hexafluoromanganates (IV) Pfeil, Achim

Abstract

The primary processes of photoexcited hexaf1uoromanganate (lV) have been investigated through spectroscopic studies. The emission and absorption spectra, emission quantum yields, and lifetimes of K₂MnF₆, Rb₂MnF₆, Cs₂MnF₆ and Mn⁴⁺ in the matrix of K₂GeF₆ and Cs₂GeF₆ have been measured as single crystals and in solution at temperatures between 10 and 600°K. The vibrational structure in the spectra has been correlated in many cases with the frequencies determined from IR and Raman spectra and origins of electronic transitions have been assigned. Phosphorescence from the ²E[sub g] state has been observed. Thermally activated reverse intersystem crossing from the ²E[sub g] to the ⁴T[sub 2g] state has been established for Cs₂MnF₆ from the occurrence of delayed fluorescence at high temperatures. The activation energy of this process is consistent with the separation of the origins of these states obtained from low-temperature high-resolution spectra. The lifetime of Mn⁴⁺ :Cs₂GeF₆ is radiative up to 450°K and only weakly dependent on temperature. The temperature dependence follows that predicted by a vibronic mechanism. Above 450°K the complex is strongly deactivated by a radiationless process which dominates the thermal activated reverse intersystem crossing. In solution a strong temperature dependent radiationless process occurs above 130°K. The nature of these radiationless processes is discussed.

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