Absorption, fluorescence, and electron spin resonance investigation of tervalent cerium activated LaMgAl11O19

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Abstract
Single crystals of the magnetoplumbite (MP)-like compounds La1−xCex MgAl11O19 (0≤x≤1) have been grown from the melt by the flame fusion method. These crystals have been characterized by optical absorption and fluorescence which occur between 4f and 5d levels as well as by electron spin resonance at 20 K. For dilute samples (x≤0.15) all of these studies agree with a distribution of cerium between two kinds of sites with C2v point symmetry but with different optical spectroscopic properties whose occupation depends on the cerium content (x value). There is no evidence of any cerium in the regular MP lanthanide site with D3h symmetry. Several structural models which could account for these results are discussed.