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

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.