Y2O3 anti-reflection films were deposited on freestanding CVD diamond substrates by radio frequency magnetron sputtering. The thermal shock resistance and oxidation resistance of Y2O3/diamond/Y2O3 samples at 727 degrees C and 800 degrees C in atmospheric air were investigated. No delamination of the Y2O3 films occurred after thermal shock, thereby demonstrating extreme adhesion to freestanding diamond substrates. After thermal shock, Y atoms in the films were almost fully oxidized. Moreover, the majority of monoclinic phase in the Y2O3 films transformed into cubic phase, crystallinity was enhanced, and the average grain size significantly increased. The maximum transmittance in the 8-12 mu m long-wave IR range of the Y2O3/diamond/Y2O3 samples increased from 81.3% +/- 0.3% to 84.7% +/- 0.2% and 83.6% +/- 0.4%. These findings indicated that the Y2O3 anti-reflection films displayed good resistance to thermal shock and provided sufficient protection for diamond substrates against elevated temperature oxidation. (C) 2016 Elsevier B.V. All rights reserved.