Ruby thermometer for cryobaric diamond-anvil cell

The ruby R-line luminescence, commonly used as a manometer in diamond-anvil cell experiments, is shown also to be a useful thermometer over the range 10–100 K. Measurements up to 120 kbar in a solid Ar pressure medium demonstrate that the intensity ratio of the two R lines is thermally activated; in agreement with elementary theory the activation energy is given by the R1–R2 splitting. Based on this dependence, the in-situ temperature of the diamond-anvil cell sample chamber can be determined with ∼10% accuracy over 10–100 K. To apply the ruby thermometer method, no additional effort is needed beyond that already incurred in the standard ruby pressure measurement. The method remains applicable under conditions of moderately nonhydrostatic pressure. The problem of laser heating is discussed.