Mechanochemical synthesis of α-Al2O3-Cr3+ (Ruby) and χ-Al2O3

In this work we present a unique method to synthesize -Al2O3 and -Al2O3 doped with Cr3+ (ruby). The ruby is synthesized by mechanical milling of pseudoboehmite that is doped in-situ with chromium. The doping is carried by adding chromium sulfate hydrate to an aqueous solution rich in aluminum sulfate hydrate. The pH in the solution is controlled to be between 9 and 10 by using ammonia, which induces the pseudoboehmite precipitation. The Cr3+ is added for its remarkable effects on the detectability of ruby emitting luminescent R-1 and R-2 bands that are traceable in Raman spectroscopy. The formation of ruby is detected at milling times as short as 5hours and increased with the milling time. Ruby phase is further confirmed by means of true atomic resolution Transmission Electron Microscopy (TEM).