Photo- and Cathodoluminescence of the Combustion-synthesized Al2O3–TiB2 Composites

Al2O3–TiB2 composites were synthesized by the combustion reaction 3TiO2 + 3B2O3 – (10 + x)Al, with x ranging from 0 to 4.71. The products consisted of corundum, TiB2, and a trace of Ti2O3 for the reactions with x = 0 and x = 1.4. However, the products of the reaction with x = 2.96 contained corundum and TiB2 only. For products of samples with x = 0, 1.4, and 2.96, similar room-temperature absorption spectra were observed in the ultraviolet and visible range at wavelengths of 265, 706, and 844 nm. Room-temperature photoluminescence spectra of the composites showed one visible band at about 720 nm. Room-temperature cathodoluminescence (CL) spectra of the composites synthesized by reactions with x = 0 and 1.4 exhibited two visible bands centered at 400 and 710 nm, respectively. From samples synthesized with x = 2.96, another visible band centered at 570 nm was observed in the CL spectrum. Comparing secondary electron images to panchromatic and monochromatic CL images of the composites, it was found that the light-emitting phase is TiB2-containing corundum. The 710-nm band is attributed to the transition between 1T1 (et) and 3T2 (et) excited states, and the 570- and 400-nm bands to the transitions between 3T1 (et) or 3A2 (e2) and 1T1 (et) excited states and 3T1 (t2) ground state of Ti2+ in corundum, respectively.