Abstracts 1999

Abstract of Publication No. 330

F. Rodriguez, D. Hernandez and H. U. Güdel
Double-excitation transitions in the perovskite NH4MnCl3 studied by pressure techniques
Phys. Rev. B 60, 10598-10601 (1999)      Full Text (PDF)      DOI-Link     

Abstract: This work investigates double-excitation (DE) transitions in the cubic chloroperovskite NH4MnCl3 through high-pressure absorption spectroscopy. This procedure has proved to be a powerful tool for revealing DE from the peak energy variations induced by pressure. Particularly, this is important for manganese chlorides where DE assignment is a difficult task to accomplish given that the associated bands appear in the absorption threshold and overlap with several Mn2 + single excitation (SE) bands. Apart from Mn2 + SE, the optical-absorption spectrum of NH4MnCl3 microcrystals shows a new intense band at 39 200 cm1 that is assigned to the 4T1g+4T1g DE transition. The proposed assignment is based on the transition energy as a sum of the corresponding SE energies, E(4T1g+4T1g) = E(4T1g) + E(4T1g), and is clearly confirmed by the variation of the band position with pressure. The measured pressure shift of E/P = -76 cm1/kbar is twice the pressure shift experienced by the first 4T1g(G) SE located at 19590 cm1, E/P = -37 cm1/kbar. From this result, the possibility of SE transitions 4A2g(F), 4T1g(F), and 4T2g(F) located around 40 000 cm1 as responsible for this band is definitively ruled out due to their different pressure shift.

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