Effect of A – Site disorder on the bonding mechanism and optical properties of Smx(Al2O3)1−x system

Samples of varying samarium (Sm) concentration doped alumina (Al2O3) were prepared by the solid state reaction method and were characterized using x-ray diffraction and Raman spectroscopy for phase identification and local structural disorder respectively. The lattice disorder induced by varying composition and the enhancement of Raman intensities in the lower wavenumber side confirms the successful incorporation of dopant ions into the host matrix. The addition of dopant ions changes the unit cell volume and crystal structure to orthorhombic with Pbnm symmetry. The extent of non-bridging oxygen atoms vary with increasing dopant concentration, which shows the varying covalent character of the titled material. This is believed to induce a substantial destabilization in the octahedral environment leading to the tilting and bending of the BO6 octahedra. UV–vis diffuse reflectance spectroscopy data analysis confirms that changing covalent character of the material induced by the destabilization in the octahedral environment. The optical band gap energy decreases, while the Urbach energy decreases with increasing non-bridging oxygen atoms.