Synthesis, Structural, Dielectric, Optical, and Luminescence Studies of Lanthanum- and Yttrium- Manganese Silicates

Apatite structured polycrystalline samples of rare earth manganese silicates, La₄MnSi₃O₁₃ and Y₄MnSi₃O₁₃, were synthesized via ceramic route, and their crystal structure, morphology, dielectric, optical, and luminescence characteristics were thoroughly examined. Rietveld refinements of the X-ray diffraction data and Raman results confirm that both the compounds are formed in single phase, and crystallize in hexagonal crystal symmetry. Scanning electron microscopy micrographs show the crystalline nature of the synthesized silicates, and the sizes of the grains are found in submicron range. The dielectric constant and tanδ show systematic variation with frequency. The low values of tanδ of these ceramic samples suggest the potential use in energy storage capacitive devices. The calculated wide band gap energies (4.3 eV and 4.03 eV) of these new compositions of silicate apatites make them useful for better absorption and emission of UV light for applications in solid state lighting devices. The photoluminescence characteristics of La₄MnSi₃O₁₃ and Y₄MnSi₃O₁₃ samples make them beautiful sources of green-yellow and green emissions, respectively.