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Among rare-earth ions Ce3+ has the simplest electron configuration - 4f1. Its 4f-5d transitions have an energy of approximately 6.3 eV for a free ion and are quite allowed. Thus, the introduction of Ce3+ into the crystal with wide enough forbidden gap makes it possible to analyze the lattice environment influence on the excited state. During the present research the following results were obtained via spectral-kinetic investigations of the excited states of Ce3+ impurity in various third group metal oxides: (a) luminescence spectrum of Ce3+ has a doublet structure in all examined oxides. This happens due to the energy split of 2F5/2 and 2F7/2 terms of Ce3+ ground state by reason of spin-orbit interaction. (b) In Al2O3 a broad 5-component band corresponding to 4f-5d transitions is observed in the long- wave region of Ce3+ luminescence excitation spectrum. In the short-wave region of excitation spectrum, one can eliminate a non-structured band, which hypothetically consists of the exciton band and the charge transfer band, and as well as an outstanding narrow exciton-band. (c) In YAP bands of 4f-5d transitions are divided into two groups in excitation spectrum: 3-component in the region of 4-5 eV and 2-component in the region of 5-6 eV. (d) In YaG 4f-5d transitions appear as separate bands in excitation spectrum: 2.9, 3.9, 4.6, 5.6, 6.6 eV. Due to the closeness of the fundamental absorption edge in YAG, the band 6.6 eV is observable only at low temperatures. (e) At temperatures under 100 K the energy transfer form exciton to impurity is not detected for all the crystals.
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