Peculiarities of photoluminescence of Al2O3 bulk and nanosize powders at low temperatures

Photoluminescence has been studied in the aluminum oxide (Al2O3) bulk and nanosize powders in the 300–8 K temperature range. In both samples luminescence spectrum is characterized by presence of broad blue and red bands caused mainly by emission from the uncontrolled titanium impurity. At low temperatures luminescence intensity increases by several times and the red band obtains fine structure. The nature of the fine structure is discussed suggesting manifestation of splitting of the Ti3+ emitting level due to Jahn–Teller effect or overlapping of Ti3+ emission band with narrow lines from other emitting ions. The observed differences in low-temperature spectral features of nanopowder compared to its bulk counterpart are explained by lattice structure of nanopowder, which belongs to transition phase of Al2O3.

Research highlights
► Photoluminescence of Al2O3 macro- and nanopowders is due to uncontrolled impurities.
► Emission spectra consist of blue (Ti4+) and red (Ti3+) bands.
► At temperature decrease luminescence intensity rises, red band obtains fine structure.
► Explanation: Jahn–Teller splitting of Ti3+ emitting level or lines of other impurity.
► Differences in spectra of two samples are explained by different structure of lattice.