Begleitbanden der Null-Phononenlinien des Phosphoreszenzüberganges dotierter Cr3+: Alha6J3-Kristalle. Teil I. Lumineszenz / The Sidebands of the zero Phonon band of the Phosphorescence Transition in Cr3+ : Alha6J3 Single Crystals. I. Luminescence

Abstract

The sidebands of the zero phonon band of the phosphorescence transition are investigated in Cr3+:Alha6J3 single crystals for several Cr (III)-concentrations. At low Cr (III)-concentrations of 2 mol-% the electronic transitions can be assigned to the zero phonon transition of the phosphorescence and the corresponding phonon sidebands with the aid of polarisation measurements, the temperature behaviour of the bands and the isotope effect. Under the influence of a trigonal field D3 combined with spin-orbit coupling, both transitions and are observed. The phonon sidebands and the internal vibrational sidebands of the transition are compared with infrared and Raman vibrational bands. At a Chromium (III) concentration of 26 mol-%, some additional bands are measured nearby the transition, which cannot be explained in the single ion crystal field model. There exists a super exchange interaction between the Cr3+-ions across the urea ligands. The interaction can be described by a Hamiltonian Hex = -JS1 · S2, which splits the 4A2-ground level into four levels | 4A2 · 4A2〉 S = 0,1,2,3 with energy differences |J|; 2|J| and 3 |J|. In the phosphorescence spectrum the four transitions |2E · 4A2)〉S' = 1 → |4A2·4A2〉s = 0,1,2,3 are observed and the value of the exchange integral is calculated.