Abstract
Abstract The three new Cr4+ doped matrices studied in this work exhibit only tetrahedrally coordinated lattice sites for the small cations and therefore will not incorporate Cr3+ ions. The Cr4+ doped compounds SrGa4O7 and Sr(Ga, Al)2O4 exhibit broad band IR fluorescence. But it appears difficult to combine easy crystal growth and good optical properties. If Cr4+:SrGa4O7 can be grown by Czochralski method, its fluorescence lifetime is very short (1 μs at 100 K). On the contrary for Cr4+:Sr(Ga, Al)2O4, the 100 K fluorescence lifetime can reach 35 μs (and 10 μs at 300 K), but the hexagonal-monoclinic structural transition prevents to grow good quality single crystals. Cr4+:Li2MgSiO4 is a remarkable compound. At 300 K it exhibits broad and intensive fluorescence peaking at ∼ 1.2 μm. The fluorescence lifetime exceeds 100 μs at 300 K and 400 μs at ∼ 50 K. This is the highest value reported so far, to our knowledge, for a Cr4+ activated material. The very long fluorescence lifetime and its temperature dependence are explained by the thermalization of the Cr4+ 3T2 and 1E levels, the 1E level being the lowest one. Crystal growth of Cr4+:Li2MgSO4 using the flux method is in progress.
Published Version
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