Rhodamine 6G is a highly fluorescent rhodamine family dye. It is often used as a tracer dye within water to determine the rate and direction of flow and transport. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with instruments called fluorometers. Rhodamine dyes are used extensively in biotechnology applications such as fluorescence microscopy, flow cytometry, fluorescence correlation spectroscopy and ELISA. Rhodamine 6G chloride powder mixed with methanol, emitting yellow light under green laser illumination; Rhodamine 6G-based dye laser. The dye solution is the orange fluid in the tubes; Rhodamine 6G is also used as a laser dye, or gain medium, in dye lasers, and is pumped by the 2nd (532nm) harmonic from an Nd:YAG laser or nitrogen laser. The dye has a remarkably high photostability, high fluorescence quantum yield (0.95), low cost, and its lasing range has close proximity to its absorption maximum (approximately 530nm). The lasing range of the dye is 555 to 585nm with a maximum at 566nm. Rhodamine 6G usually comes in three different forms. Rhodamine 6G chloride is a bronze/red powder with the chemical formula C27H29ClN2O3. Although highly soluble, this formulation is very corrosive to all metals except stainless steel. Other formulations are less soluble, but also less corrosive. Rhodamine 6G perchlorate (C27H29ClN2O7) comes in the form of red crystals, while rhodamine 6G tetrafluoroborate (C27H29BF4N2O3) appears as maroon crystals.