Microstructure of luminescent MgAl₂O₄ nanoceramics

Luminescent transparent nanoceramics were obtained by thermobaric treatment (TBT) of magnesium aluminium spinel nanopowder. The morphological features were studied by scanning electron microscopy combined with X-ray powder diffraction. Obtained ceramics do not have any agglomerates and pores larger than 100 nm. Crystallites have a high size uniformity. An increase in the lattice constant of nanoceramics compared to the initial powder is observed. Under the TBT, a decrease in the region of coherent scattering due to elastic deformation of crystallites is found. The absence of cracks, large pores, nanosize grains, and high size uniformity reduce light loss in the material, increasing its transparency. Point defects were characterized by photoluminescence and electron spin resonance (ESR) methods. The glow in the 1.8 eV band is caused by the presence of Ti³⁺ impurity ions. An abnormally wide peak with a maximum at 2.4 eV in the photoluminescence spectrum is recorded. This signal is a superposition of the Mn²⁺ ions emission bands and oxygen vacancies (F and F⁺ centres). In the ESR spectrum, signals from impurity ions of iron, titanium, and manganese, as well as an intense signal at g = 2.005 associated with oxygen vacancies in nanoceramics were detected. (paper)