Chromium Pairs in Combustion Synthesized α-Alumina

High surface area alumina has gained much attention as a support structure for a number of possible biological and biomedical applications. Combustion synthesis provides a simple route to produce large quantities of alumina with optically active impurities after liquid phase mixing. In this report, we present results on chromium ion separation in combustion-synthesized highly-doped ruby. Aluminium and chromium nitrates are dissolved in water/urea solutions. The solutions are then heated above 500 degrees, at which point they undergo a self-propagating combustion reaction transforming them into high-surface area solids. X-ray diffraction confirms the single phase a-alumina structure. Optically excited fluorescence (excited at 473 nm) spectra are used to measure the ratio of the fourth nearest neighbour emission peak to that of the single ion peak to quantify impurity pair formation as a function of chromium concentration. The ratio increases linearly over the concentration range up to four atomic percent. Time-resolved decay dynamics of the pairs will be presented.