Fluorescence and absorption of rhodamine 6G solutions as pressure standards for a diamond-anvil cell

The absorption and fluorescence spectra of rhodamine 6G (R6G) dissolved in water, methanol, ethanol and isopropanol have been applied to calibrate the pressure in a diamond anvil cell (DAC). Owing to the strong initially nearly linear temperature-independent bathochromic shift of 7 nm GPa-1 found in absorption and emission bands for methanol R6G solutions, they are ideal for precise pressure calibration to over 3.4 GPa, when methanol freezes. Analogous bathochromic shifts as a function of pressure are revealed for aqueous, ethanolic and isopropanolic solutions. The pressure-induced shifts are considerably reduced in the crystallized solution. Practical protocols are presented to calibrate high pressures with R6G solutions. Absorbance and fluorescence of rhodamine 6G solutions provide two independent methods of convenient and accurate high-pressure calibration, hardly temperature-biased and adjustable to different experimental requirements.